Edo Waks

Maryland Nanophotonics Laboratory, Office: Kim Engineering Building, Rm. 2132, University of Maryland, College Park, MD 20742-3511

I will describe our effort to attain scalable quantum photonic devices using quantum dots. I will first describe a quantum transistor where a single photon can control a quantum dot spin and vice versa. This switch realizes a transistor operating at the fundamental quantum limit, where in picoseconds timescales a single photon flips the orientation of a spin and the spin flips the polarization of the photon. Such spin-photon interactions provides the key mechanism to achieve photon-photon interactions and generate photonic entanglement, which is one of the two central requirements for photonic quantum information. In particular, I will then show how to exploit these interactions to achieve strong interactions between photons and attain a single photon transistor.  Finally, I will describe new fabrication methods based on hybrid integration of quantum dots with silicon and lithium niobate to scale quantum photonic circuits to many-emitter systems.  

Marlon Placke^1,2, Sven Ramelow¹

¹Nichtlineare Quantenoptik, Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
²Ferdinand-Braun-Institut, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany

We present AlGaAs-on-insulator waveguides as a promising nonlinear optics platform with C-band compatibility [1]. Combination of the compound’s ultra-high material nonlinearity with nanoscale mode confinement renders possible nonlinear photon interactions that could, in principle, become efficient even at single-photon-level seed powers e.g. in four-wave mixing schemes that employ non-degenerate pump fields of vastly different amplitudes [2, 3]. To phase-match second- and third-order nonlinear optical processes, we exploit the platform’s inherently tunable waveguide dispersion that results from the large refractive index contrast of the core and cladding material. Furthermore, prudent choice of the compound’s Aluminum fraction enables strong pumping by shifting two-photon absorption beyond the telecom window. Finally, owing to (Aluminum-)Galliumarsenide’s direct bandgap and the maturity of established fabrication techniques, the possibility of on-chip pump integration could inspire future devices, such as integrated sources of entangled photon pairs from broadband spontaneous parametric downconversion with applications in (wavelength division multiplexed) quantum key distribution.

We here present how χ⁽²⁾-efficiencies are optimized through careful balancing of the mode confinement with the three-wave mixing overlap. The procedure yields downconversion efficiencies of 10^-5 pairs per pump photon for simple rectangular waveguides that can further be enhanced in microring resonators [1].

Paweł Mrowiński¹, Peter Schnauber¹, Philipp Gutsche², Arsenty Kaganskyi¹, Johaness Schall¹, Sven Burger², Sven Rodt¹, Stephan Reitzenstein¹

¹Technische Universität Berlin, Hardenbergstraße 36, D-10623 Berlin, Germany
²Zuse Institute Berlin, Takustraße 7, D-14195 Berlin, Germany

Quantum dots embedded in waveguides can exhibit directional emission or non-reciprocal transmission on a single-photon level via chiral light-matter interactions, which is important for the realization of large-scale on-chip quantum circuits [1,2]. In this work, we study directional emission of single InGaAs/GaAs quantum dots (QD) in ridge Bragg reflection waveguide (WG) structures. The QDs is pre-selected and deterministically integrated into the WGs by using in-situ electron-beam lithography [3] to systematically explore the dependence of chiral coupling on the positions of single QDs inside the waveguides. The directional propagation is reflected in the polarization resolved photoluminescence for the outcoupled light, which can be influenced by the external magnetic field applied in Faraday configuration. A significant contrast of ~90 % is observed for right/left circularly polarized QD emission from charged exciton in case of QD located at highly off-center position, which indicates chiral coupling in this system. Furthermore, we study in detail the contrast vs QD position dependence and we obtain good agreement with the calculated dependence by Finite Element Method (JCMwave) including several propagatin modes. These results confirm the tight control of chiral effects in deterministically fabricated QD-waveguide systems with high potential for future non-reciprocal on-chip systems required for quantum information processing.

Tommaso Calarco

Forschungszentrum Jülich GmbH, JARA-Institute Quantum Information (PGI-11), 52425 Jülich

The control of quantum states is essential both for fundamental investigations and for technological applications of quantum physics. In quantum few-body systems, decoherence arising from interaction with the environment hinders the realization of desired processes. In quantum many-body systems, complexity of their dynamics further makes state preparation via external manipulation highly non-trivial. An effective strategy to counter these effects is offered by quantum optimal control theory, exploiting quantum coherence to dynamically reach a desired goal with high accuracy even under limitations on resources such as time, bandwidth, and precision. In this talk I will:

- introduce the quantum optimal control method we developed to this aim, the CRAB (Chopped Random Basis) algorithm, which is to date the only method that allows to perform optimal control of quantum many-body systems;

- present experimental results obtained via its application to various physical systems, from quantum logical operations in solid-state quantum optics to quantum criticality in ultra-cold atoms, both in open-loop and in closed-loop feedback scenarios, with applications ranging from quantum interferometry with Bose-Einstein condensates on atom chips to magnetic field sensing in diamond NV centers and to the preparation of optical-lattice quantum registers for quantum simulation;

- use these examples to illustrate the quantum speed limit, i.e. the maximum speed achievable for a given quantum transformation, and describe related effects of nonlinearity due to inter-particle interactions and more in general to dynamical complexity;

- illustrate a recent experiment in which our algorithm competed against human players in an online game aiming at reaching the speed limit for the remote preparation of a Bose-Einstein condensate in an actual lab.

Vojtěch Švarc, Martina Nováková, Glib Mazin, Miroslav Ježek

Department of Optics, Faculty of Science, Palacký University, 17. listopadu 12, 77146 Olomouc, Czech Republic

Fast splitting, switching, and routing of light are critical tools of photonic technology in the rapidly developing fields of optical communication and optical information processing including demanding applications like quantum cryptography [1], quantum computing [2], and photon counting [3]. High-efficiency single-photon generation has been demonstrated employing active time multiplexing [4-6]. Also, many tests of fundamental physics are facilitated by optical switching [7]. We report a 2x2 photonic coupler with arbitrary splitting ratio tunable by an external electronic signal with 10 GHz bandwidth, 10 ns latency, and the amplitude lower than 2.5 V. The coupler is based on a single Mach-Zehnder interferometer in dual-wavelength configuration, which allows for real-time phase lock with stability better than 1 deg. The coupler can be set to any splitting ratio from 0:100 to 100:0 with the extinction ratio of 26 dB. We demonstrate the operation of the coupler by 100 ps switching between various regimes such as balanced 50:50 beam splitter, 0:100 switch, and a photonic tap. Furthermore, using the reported device, we demonstrate for the first time the perfectly balanced time-multiplexed device for photon-number-resolving detectors and also the active preparation of a photonic temporal qudit state up to four time bins.

Gioan Tatsi, Luca Mazzarella, John Jeffers

Department of Physics, University of Strathclyde, John Anderson Building, 107 Rottenrow Glasgow, G4 0NG

Photon subtraction¹ is a process by which photons are removed from a mode of the electromagnetic field. It has been shown that this non-unitary operation, realisable probabilistically using a beam splitter, a vacuum auxiliary state and a photodetector, can lead to counterintuitive results such as preservation of the mean photon number of coherent states and increase of the mean photon number of thermal states^2,3. It is used in many applications ranging from amplification of the amplitude of quantum states⁴ to generation of Schrödinger cat states¹.

Thermal states have played an important role in experiments such as that of Hanbury-Brown and Twiss⁵. The application of photon subtraction to thermal states has shown phenomena such as the “quantum vampire” effect⁶ and the possibility to realise an all photonic Maxwell demon⁷.

In this work we investigate the effect on thermal states of a process that we dub displaced photon subtraction, in which we displace a thermal state and then perform a photon subtraction whose auxiliary state is an anti-displacing coherent state. We show that displaced photon subtraction can lead to a “cooling” effect on input thermal states and that this can be harnessed to realise a linear optical photonic Maxwell demon.

Radim Hošák, Robert Stárek, Miroslav Ježek

Palacky University Olomouc, 17. listopadu 12, 77146 Olomouc, Czech Republic

Quantum tomography is an essential method of the photonic technology toolbox and is routinely used for evaluation of experimentally prepared states of light and characterization of devices transforming such states. As the size of the studied system grows, the number of measurements required for full tomography increases in a non-polynomial fashion. This presents a great challenge and incentivizes us to reduce the overall duration of the tomographic procedure, so that time is saved and the effect of setup drift reduced. For many physical realizations of the quantum states, including polarization and path-encoded qubits, a traveling salesman problem of finding the optimal order of tomographic projections can be found and solved. The achieved tomography speedup, found and experimentally verified for up to six-qubit systems, is seen to increase with the size of the system in question. For three-qubit systems already, the time spent on setting the measurement projections can be halved [1]. A step-by-step workflow is introduced to suit various tomographic scenarios and experimental platforms, for example reducing the overall heat dissipation in photonic on-chip circuits. The presented optimization is beneficial not only for high-dimensional state tomography but also for multi-copy characterization schemes.

Rainer Blatt

Institute for Experimental Physics, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Otto-Hittmair-Platz 1, A-6020 Innsbruck, Austria

The state-of-the-art of the Innsbruck trapped-ion quantum computer is reviewed. First, we present an overview on the available quantum toolbox and discuss the scalability of the approach. Fidelities of quantum gate operations are evaluated and optimized by means of cycle-benchmarking and we show the generation of a 16-qubit GHZ state. Entangled states of a fully controlled 20-ion string are investigated and used for quantum simulations.
In the second part, we present both the digital quantum simulation and a hybrid quantum- classical simulation of the Lattice Schwinger model, a gauge theory of 1D quantum electrodynamics. Employing universal quantum computations, we investigate the dynamics of the pair-creation and using a hybrid-classical ansatz, we determine steady-state properties of the Hamiltonian. Hybrid classical-quantum algorithms aim at solving optimization problems variationally, using a feedback loop between a classical computer and a quantum co-processor, while benefitting from quantum resources.

Filip Sośnicki, Michał Mikołajczyk, Ali Golestani, Michał Karpiński

Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warszawa, Poland

Recently much effort has been directed towards shaping time-frequency (TF) mode structure of light for the purpose of high-dimensional quantum information processing. Such manipulations require unitary, phase-only operations, which can be realized by combining dispersive propagation with applying a time-dependent phase by direct electro-optic phase modulation (EOPM). Especially one can create a time lens, which consists of applying a time-varying quadratic phase on the optical pulse [1]. Then one can combine the two above operations achieving bandwidth compression [2]. By using more time lenses, thus creating a time-lensing system, one can increase the modulation depth of an applied phase, resulting e.g. in a higher bandwidth compression. The setup could also manipulate the joint spectral intensity (JSI) of entangled photons, by applying bandwidth compressors on both photons.

We have experimentally implemented a stable system of two EOPM-based time lenses driven by an amplified RF signal generated by a fast photodiode. We demonstrate a frequency shear of light pulses in range of 2 nm and their bandwidth compression by a factor exceeding 8. We modify the JSI of pairs of entangled photons. Our results indicate that optically driven EOPM-based time-lensing system allows for a low-loss, low-jitter shaping of quantum light pulses.

Thomas Lettner¹, Katharina D. Zeuner¹, Huiying Huang², Selim Scharmer¹, Saimon Filipe Covre da Silva², Eva Schöll¹, Lucas Schweickert¹, Armando Rastelli², Klaus D. Jöns¹, Val Zwiller¹

¹Quantum Nano Photonics, Department of Applied Physics, KTH Royal Institute of Technology, Albanova University Centre, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
²Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz, Austria

Optically active semiconductor quantum dots (QDs) are excellent single-photon sources [1] with tailorable optical properties [2]. We work with highly symmetric QDs of gallium arsenide (GaAs) infilled holes obtained by aluminium (Al) droplet etching in Al0.4Ga0.6As [3].

In order to utilize those QDs we develop new structures to efficiently couple the single photons out of the semiconductor material and into the collection optics of our micro-photoluminescence (μ-PL) experiment. For this, we employ a low-Q microcavity with a metallic gold backside mirror. Precise control of the microcavity sidewall curvature allows us to achieve a parabolic backside mirror shape and enhanced μ-PL intensity with an estimated extraction efficiency of 12.5%.

Furthermore, we integrate our QD microcavity structures onto 200 μm thick PMN-PT piezoelectric substrates using a polymer-based bonding process. The piezo allows us to induce a large in-plane biaxial strain into the semiconductor material at low temperature. With our devices, we tune the emission of the QDs with planar (parabolic) metallic backside mirror by 1 meV (0.4 meV) for 400 V applied to the piezo, in a dynamic, reversible and linear way.

Junmin WANG

Institute of Opto-Electronics, Shanxi University, No.92 Wu Cheng Road, Tai Yuan 030006, Shan Xi province, China

Atoms trapped in a magic-wavelength optical tweezer will have the same light shift for the desired ground and excited states, therefore the position-dependence differential light shift can be eliminated. For cesium 6S_1/2 (4, +4) - 6P_3/2 (5, +5) transition at 852 nm, the magic wavelength of optical tweezer was calculated theoretically and verified experimentally to be 937.6 nm for a linearly-polarized tweezer beam. Narrow-band 852-nm single-photon sources based on a single cesium atom trapped in optical tweezer with 1064-nm (937.6-nm) laser beam have been implemented. Strong anti-bunching effect, g^(2)(Tao=0) = 0.09, was demonstrated. The Hong-Ou-Mandel two-photon interference was employed to evaluate the photon indistinguishability. Preliminary results indicate that the photon indistinguishability has been improved ~ 20% for the case of magic-wavelength 937.6-nm optical tweezer, compared with the 1064-nm case. Photon indistinguishability is vital for the Boson sampling and the linear optics quantum computation with single photons.

Rinaldo Trotta

Department of Physics, Sapienza University of Rome, 00185 Rome, Italy

Quantum teleportation and entanglement swapping are essential resources to the realization of quantum networks. These quantum phenomena are built up around the non-local properties of entangled states of light that, in the perspective of real-life applications, should be encoded on photon-pairs generated on-demand. Despite recent advances, however, the exploitation of deterministic quantum light sources in all-photonic quantum teleportation and entangled swapping protocols remains a major open challenge. In this talk, I will show that photons generated on-demand by a GaAs quantum dot can be used to implement a teleportation protocol whose fidelity violates the classical limit for any arbitrary input states [1]. Moreover, I will present the first experimental demonstration of all-photonic entanglement swapping using pairs of entangled photon generated by a quantum emitter [2]. A discussion on future perspectives will conclude the talk.

Eva Schöll¹, Lukas Hanschke², Lucas Schweickert¹, Katharina D. Zeuner¹, Marcus Reindl³, Saimon Filipe Covre da Silva³, Thomas Lettner¹, Rinaldo Trotta⁴, Jonathan J. Finley², Kai Müller², Armando Rastelli³, Val Zwiller¹, Klaus D. Jöns¹

¹Department of Applied Physics, Royal Institute of Technology, Albanova University, Centre, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
²Walter Schottky Institut and Physik Department, Technische Universität München, 85748, Garching, Germany
³Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040, Austria
⁴Dipartimento di Fisica, Sapienza Università di Roma, Piazzale A. Moro 1, I-00185 Roma, Italy

In recent years’ single-photon based quantum technologies, offering the only reliable flying qubit to transmit quantum information, have gotten substantial attention not only from the scientific community but also from industrial stakeholders.

Since then GaAs quantum dots obtained by the Aluminium droplet etching technique have started to emerge as ideal candidates for these photonic quantum technologies, holding the record for the purest single-photon source [1], the brightest entangled photon pair source [2], as well as being the only on-demand source reaching entanglement fidelities near-unity [3]. However, another crucial parameter, near-unity indistinguishability of the emitted photons has proven to be elusive for these quantum emitters. Here, we show for the first time near-unity indistinguishability with a record-breaking raw visibility of V=94.2(5.2) %, without any data fitting nor correction for setup imperfections. We perform the first pulsed resonance fluorescence on these novel solid-state quantum emitters, revealing fast dynamics during the coherent control of the quantum mechanical V-system thanks to our low noise, high time resolution single-photon detectors.

Our results open the way for these emitters to be used as basic building blocks in quantum communication applications, such as sources for quantum repeaters.

Severin Daiss¹, Bastian Hacker¹, Stephan Welte¹, Lin Li^1,2, Gerhard Rempe¹

¹Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany
²Present address: School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China

Pure single photons are a key to many future quantum-communication technologies and especially to quantum networks. Despite their importance, they are difficult to produce with the required quality. To date, various light sources have been able to strongly suppress contributions of two and more photons. However, the elimination of the electromagnetic vacuum remains a challenging task, albeit a lot of effort has been put into the removal of limiting perturbations. Here, we follow a different approach and distill single photons out of incoming light pulses. We use the reflection of the light from an atom-cavity system and employ a suitable measurement of the atom to herald the success of the operation. We create single-photons with custom-made temporal shapes and a fidelity of 66% out of initial vacuum-dominated coherent pulses. Our scheme could further be used to boost the fidelity of single-photon sources without any fundamental limit. As it only requires an emitter coupled to a resonator, our protocol can be a valuable tool to distill single photons in a wide range of different experimental platforms.

Anna Musiał¹, Nicole Srocka², Kinga Żołnacz³, Monika Mikulicz¹, Jakub Jasiński¹, Paweł Holewa¹, Jan Große², Wacław Urbańczyk³, Philipp-Immanuel Schneider⁴, Sven Burger^4,5, Krzysztof Poturaj⁶, Grzegorz Wójcik⁶, Paweł Mergo⁶, Kamil Dybka⁷, Mariusz Dyrkacz⁷, Michał Dłubek⁷, David Quandt², André Strittmatter², Sven Rodt², Stephan Reitzenstein², Grzegorz Sęk¹

¹Laboratory for Optical Spectroscopy of Nanostructures, Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wrocław, Poland
²Institute of Solid State Physics, Technical University of Berlin, Berlin, Germany
³Fiber Optics Group, Department of Optics and Photonics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wrocław, Poland
⁴JCMwave GmbH, Berlin, Germany
⁵Zuse Institute Berlin, Berlin, Germany
⁶Laboratory of Optical Fiber Technology, Maria Curie-Skłodowska University, Lublin, Poland
⁷Fibrain Sp Zoo, Zaczernie, Poland

The goal of our work is to demonstrate a stand-alone single-photon source operating at the telecom O-band applicable in short-range ultra-secure communication. Single photons of high purity (g(2)(0)<1%) [1] and on demand [2] are generated by InGaAs/GaAs quantum dots (QDs) covered with a strain reducing layer to redshift their emission to 1.3 µm range [3,4]. For enhanced extraction efficiency a single QD is deterministically incorporated into a photonic mesa structure (50 nm accuracy) on a distributed Bragg reflector according to a numerically-optimized design [5] indicating an achievable extraction efficiency of 54%. The sample is processed deterministically by in-situ electron-beam lithography [6] – a technology successfully transferred from short wavelengths to telecom range [1] - and allowed for an experimentally-obtained extraction efficiency exceeding 15%. The stand-alone source is realized based on a Stirling cryocooler [7] with 38K operation temperature and a fiber-coupled excitation and detection system with special, highly Ge-doped single-mode fiber (NA=0.4) in a ferrule glued directly to the sample surface. The positioning of the fiber with respect to the center of the mesa is realized at room temperature using an interference method based on the signal back-reflected from the sample surface giving 50 nm in-plane accuracy [8].

Giovanna Morigi

Universität des Saarlandes, Postfach 15 11 50, D-66041 Saarbrücken

We discuss the dynamics of one-dimensional Bose-Hubbard models describing ultracold atomic ensembles interacting via cavity-mediated forces and in presence of disorder. We show that in the presence of local disorder the dynamics can manifest signatures of many-body localization. When the long-range interactions are disordered, these give rise to superglass to superfluid phases which exhibit exotic critical properties. We discuss how these features can be revealed in the light emitted by the resonator.

Janik Wolters¹, Gianni Buser¹, Roberto Mottola¹, Chris Müller², Tim Kroh², Richard Warburton¹, Oliver Benson², Philipp Treutlein¹

¹Uni Basel, Klingelbergstr. 82, CH-4056 Basel
²Humboldt-Universität zu Berlin, Newtonstr. 15, D-12489 Berlin

Quantum memories are an essential ingredient for quantum repeaters [1] and an enabler for advanced optical quantum simulators [2].

We implemented a broadband optical quantum memory with on-demand storage and retrieval in hot Rb vapor [3]. Operating at the Rb D2 line, the versatile memory is suited for storing single photons emitted by an GaAs droplet quantum dots [4,5] or single photons from spontaneous parametric downconversion (SPDC) sources [6].

We report on our recent achievements: reducing the readout noise far below the single input photon equivalent (μ1 ≪ 1) while keeping the end-to-end efficiency at about 4 %; increasing the memory lifetime to several μs; storage of true single photons with a bandwidth of ∼ 150 MHz, generated by a cavity enhanced SPDC source with 40 % heralding efficiency

With the present performance, we can already significantly increase the multi-photon rate for higher order interference experiments, e.g. for linear optical quantum simulation and computation.

Martin von Helversen¹, Jonas Böhm¹, Marco Schmidt^1,2, Manuel Gschrey¹, Jan-Hindrik Schulze¹, André Strittmatter^1,3, Sven Rodt¹, Jörn Beyer², Tobias Heindel¹, Stephan Reitzenstein¹

¹Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin, Germany
²Physikalisch Technische Bundesanstalt, Abbestraße 2-12, 10587 Berlin, Germany
³Institut für Experimentelle Physik, Otto-von-Guericke Universität Magdeburg, PF4120, Magdeburg, Germany

Semiconductor quantum dots (QDs) are promising candidates for applications in quantum photonics and quantum communication, as high levels of single-photon purity as well as indistinguishability have been reported [1,2]. These properties are usually assessed via time-correlated measurements using standard ‘click’ detectors in either Hanbury-Brown and Twiss (HBT-) or Hong-Ou-Mandel (HOM-) type configurations. Yet more complex schemes, such as photonic boson sampling [3], will involve multi-photon Fock states and it seems natural to employ true photon-number-resolving (PNR) detection systems for their characterization.

In this work, a two-channel detection system based on superconducting transition-edge sensors (TESs) [4] is used to directly access the photon-number distribution of deterministically fabricated solid-state single-photon sources. The obtained results reveal excellent quantitative agreement of the degree of indistinguishability obtained with PNR (90 ± 7 %) and standard detectors (90 ± 5 %) [5]. This demonstrates the perfect suitability of TES-based detection systems for the quantum metrology of non-classical light sources.

Subhadip Ghosh

School of Chemical Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar-752050. India

Analyses of photo-physical processes in semiconductor nanoparticles including Förster Resonance Energy Transfer (FRET), Photo-induced Electron Transfer (PET) are often complicated by a number of factors; like, close emissions of donor and acceptor, presence of fluorescence blinking, and natural excited state decay processes.^1-3 Addressing these concerns mostly from material chemists and biologists, herein we propose an efficient protocol utilizing the bright green emission of fluorescent quantum dots (FQDs). Fluorescence integrity of FQD along with the uniqueness of our analysis methods demonstrates the potential of these FQD particles in various opto-electrical applications. Molecular distance calculations relying on proposed FRET analysis complement nicely with our spectroscopic results; where FQD as a photoluminescent marker is electrostatically attached to a compatible fluorescent dye rhodamine-6g (R6g).¹ The beneficial aspect of our state-of-art analysis methods enable many possibilities, including the use of low cytotoxic QD based FRET assays as a next generation molecular ruler for a precise distance measurement inside biological systems. We also studied the excitation dependent emission of fluorescent carbon dots (FCDs).⁴ We found ground state heterogeneity and impurities in FCD sample led to many misleading interpretations, published in carbon dot literature.  Sample purification with more scientific rigor is highly warranted for FCD samples.

J. G. Rarity

Quantum Engineering Technology Labs and Quantum Engineering Centre for Doctoral Training, H. H. Wills Physics Laboratory and, , Department of Electrical & Electronic Engineering, University of Bristol, BS8 1FD, UK

Photons are well known as carriers of information in quantum secured key distribution, as gatherers of information in quantum metrology and processors of information in quantum computing. We have made great strides in linear optics quantum information processing in Bristol developing various integrated photonic chips [1] demonstrating complex quantum information [2] and simulation tasks [3] and I will present a sample of progress at the conference.

Our work is also focused on imaging/sensing technologies and I will showcase our sub-shot noise images [4] and recently developed practical schemes for photon limited sensing at long wavelengths [5]. 

I will leave you with some foundational questions as to how one might communicate without exchanging photons [6] and implications for physics. 

Mihir Bhaskar¹, Christian Nguyen¹, Denis Sukachev¹, Bartholomeus Machielse^1,2, Ruffin Evans¹, Ralf Riedinger¹, David Levonian¹, Erik Knall², Pavel Stroganov¹, Hongkun Park³, Fedor Jelezko⁴, Marko Loncar², Mikhail Lukin¹

¹Department of Physics, Harvard University, 17 Oxford Street, Cambridge, Massachusetts 02138, USA
²John A. Paulson School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA
³Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA
⁴Institute for Quantum Optics, University Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany

Quantum optical networks have the potential to enable several applications including secure, long-distance communication, enhanced sensing and metrology, and distributed quantum computing. These networks require quantum nodes capable of storing quantum information for long times, performing single and multi-qubit gates with high-fidelity, and interfacing coherently with optical photons. We demonstrate such quantum network nodes based on silicon-vacancy (SiV) color-centers coupled to diamond nanocavities [1]. As a result of strong SiV-photon coupling, we observe controllable, spin-dependent cavity photon-mediated interactions between pairs of SiV centers in a single nanodevice [2]. By cooling devices down below 500 mK [3], we demonstrate exceptional spin coherence times of nanocavity-coupled SiV center spins exceeding 1 ms. Finally, we demonstrate high-fidelity (F > 0.95), universal control over a cavity-coupled two-qubit register consisting of an SiV center and a proximal 13C with coherence time approaching 1 s, forming the basis for a first-generation integrated quantum network. As the first application of our quantum network node, we discuss the implementation of a memory-based quantum key distribution protocol that can operate at rates exceeding the bounds of direct photon transmission.

Timm Kupko¹, Lucas Rickert¹, Martin von Helversen¹, Alexander Schlehahn¹, Sven Rodt¹, Christian Schneider², Sven Höfling^2,3, Stephan Reitzenstein¹, Tobias Heindel¹

¹Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin, Germany
²Technische Physik, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
³SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, United Kingdom

Tremendous progress has been achieved in the engineering of solid-state-based non-classical light sources during the last two decades. In this context, quantum-light sources based on semiconductor quantum dots (QDs) are of particular interest. Allowing for the generation of close-to-ideal flying qubits these devices are predestined for implementations of quantum communication.

In my contribution, I will review our progress in this field, striving towards the ultimate goal of a global secure communication. I will revisit first proof-of-concept quantum key distribution (QKD) experiments using single-photon emitting diodes [1,2] and discuss the development of state-of-the-art components for QKD, such as plug-and-play single-photon sources [3] and receiver modules [4]. In this context, the metrology of the quantum light sources together with a thorough security analysis of the measurement devices is crucial for implementations of QKD. Assembling these building blocks to finally realize functional multi-user quantum-secured communication networks is a grand challenge in photonic quantum technologies, which is tackled within my recently founded Junior Research Group [5] at Technische Universität Berlin.

Jan Arenskötter, Stephan Kucera, Pascal Eich, Matthias Kreis, Philipp Müller, Jürgen Eschner

Universität des Saarlandes, AG Quanten-Photonik, Campus E2.6, 66123 Saarbrücken, Germany

In the context of quantum communication technologies, we are developing a comprehensive set of experimental tools, based on single photons and single atoms (trapped ions), that enable controlled generation, storage, transmission, and conversion of photonic qubits in quantum networks.  Such tools are required, for example, in quantum repeater protocols for reliable intermediate storage of quantum information.

Specifically, we implemented a programmable atom-photon interface, employing controlled quantum interaction between a single trapped ⁴⁰Ca⁺ ion and single photons. The interface serves as a bi-directional atom-photon quantum state converter or as a source of entangled atom-photon states [1]. We used the latter to demonstrate entanglement-preserving single-photon frequency conversion to the telecom range [2]. The interface also allows us to integrate single atoms with entangled photon pairs from spontaneous parametric down-conversion (SPDC). Our SPDC source generates polarization-entangled Bell states, tailored to match the atomic D_5/2 – P_3/2 transition at 854 nm. We demonstrated the distribution of entanglement by heralded absorption of one photon of a pair, as well as quantum teleportation of an atomic state to the other photon of the pair.

Hugo Zbinden

GAP-Quantum Technologies, Université de Genève, Chemin de Pinchat 22, , CH-1211 Genève 4

The single photon detector is a key component of every Quantum Key Distribution System. The detector noise can limit the maximum distance. At short distance the maximum key generation rate is limited by the maximum count rate,  and the maximum clock rate of the system is restricted by the timing jitter of the detectors. In this talk, we present a state of the art high speed QKD system, allowing for distributing secret keys over more than 400 km will. We detail which improvements lead to this record, and in particular the role of the superconducting detectors developed for this purpose.

Luca Mazzarella¹, Carmen Palacios Berraquero², Mustafa Gundogan², Mete Atature², Daniel Oi¹

¹John Anderson Building, 107 Rottenrow E, Glasgow G4 0NG, UK
²Rutherford Building, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK

Satellite Quantum key distribution (QKD) overcomes the range limitations of fibre-based methods to enable intercontinental secure communicaiton^1,2,3. Originally⁴ QKD protocols employed single photon sources (SPSs) but in their absence, the vast majority of QKD experiments use weak coherent pulses (WCP)^5,6. To mitigate against photon number splitting attacks, WCP sources require the use of decoy states and associated processing that could potentially compromise performance⁷.

The significant improvement⁸ in purity, indistinguishability and rate of SPSs could provide an advantage in key rate and processing with respect to current QKD sources^9,10, especially for satellite QKD where their more ideal source characteristics could lead to better performance with highly variable, high loss channels^1,3. However, manufacturability of SPS systems has remained the main barrier to their practical implementation. Recent advances on practical, scalable SPS systems now means they are becoming a real alternative to existing QKD sources. Specifically, arrays of on-chip single-photon sources operating at room temperature and in the visible range have been recently developed based on 2-dimensional material engineering^11,12,13, leading to research towards assessing the opportunity for their commercialisation.

In this work, we benchmark the use of WCP+decoy state and SPSs for satellite QKD. We consider different orbital configurations and finite block-size effects.

Mariella Minder^1,2, Mirko Pittaluga^1,3, George L. Roberts^1,2, Marco Lucamarini¹, James F. Dynes¹, Zhiliang Yuan¹, Andrew J. Shields¹

¹Toshiba Research Europe, 208 Science Park, Cambridge, CB4 0GZ, UK
²Cambridge University Engineering Department, 9JJ Thomson Avenue, Cambridge, CB3 0FA, UK
³School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK

Quantum key distribution (QKD) allows users to generate shared encryption keys that are guaranteed to be theoretically secure by the laws of quantum mechanics. Due to the use of dim optical pulses and losses in the quantum channel, there is a fundamental rate-distance limit in QKD that was thought to be unsurpassable with current technology[1]. The recent proposal of the Twin-Field QKD (TF-QKD) protocol[2] promises to overcome this limit and predicts the same square root dependence of key rate on channel loss that a quantum repeater offers, using twin light fields to carry quantum information. Here we provide the first experimental validation of this prediction by implementing TF-QKD over channel losses exceeding 90dB. This result was achieved through an interferometric setup where the two users phase encode and randomise light fields which are sent through two quantum channels for interference at a third untrusted node. The phase was stabilised and locked with an optical phase-locked loop distributed between the two transmitter users. The acquired key rate in the high-loss regime evidences for the first time that the repeaterless rate-loss limit[3] can be experimentally surpassed.

Karolina Sedziak-Kacprowicz, Mikołaj Lasota, Piotr Kolenderski

Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland

In long-distance quantum communication scheme the effect of temporal broadening during its propagation through dispersive media can considerably limit the efficiency of temporal filtering. I will review our method to significantly reduce the problem of temporal broadening proposed in Refs [1,2]. Also we demonstrate how tailoring the spectral entanglement and applying a time-resolved heralding procedure can substantially narrow the wavepacket of the propagated photons in comparison with the classical case [3]. Next, I will present how this experimental technique combined with a proper control of the pump spectral mode can be used to generate and measure entangled qudit pairs encoded in temporal modes of photon pair [4].

Aron Vanselow, Paul Kaufmann, Helen Chrzanowski, Sven Ramelow

Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany

Optical coherence tomography (OCT) allows for scanning layered systems in depth, offering information about the positions and reflectances of all the sample’s reflective surfaces. To penetrate deeply enough, in many materials mid-infrared light is required because absorption or scattering is too strong in the visible and near-IR ranges. This applies to layers of paint on artworks and channels in ceramics, used for microfluidics, as well as plastics and semiconductors. However, so far, mid-IR detectors have been too noisy and inefficient and broadband sources too complex and expensive to commercially establish mid-IR OCT.

A nonlinear interferometer circumvents these problems by exploiting the interference and frequency entanglement of photon pairs created by spontaneous parametric down-conversion (SPDC) in a nonlinear crystal. In our case, one of the photons is in the mid-IR and probes the sample while its near-IR partner photon never interacts with the sample. However, its detection with an efficient and uncooled off-the-shelf spectrometer reveals the full information about the phase that the mid-infrared photon acquired in the sample. Using very broadband SPDC in a specially designed crystal enables us for the first time to implement frequency-domain OCT with undetected photons and to experimentally demonstrate its high resolution and sensitivity.

Yuuki Tokunaga¹, Hayato Goto², Takeru Utsugi³, Takao Aoki³

¹NTT Secure Platform Laboratories, NTT Corporation, Musashino 180-8585, Japan
²Frontier Research Laboratory, Corporate Research & Development Center, Toshiba Corporation, Kawasaki, Kanagawa 212-8582, Japan
³Department of Applied Physics, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan

We show that the upper bound the success probabilities of cavity-QED-based single photon generation with the stimulated Raman adiabatic passage is expressed by using 'internal cooperativity', which is introduced here as the single-atom cooperativity parameter with respect to the cavity internal loss rate, instead of the cavity total loss rate. This is the consequence of the tradeoff relation on the cavity-QED system between the internal generation efficiency and the escape efficiency of single photon. The optimal point is given by adjusting cavity external loss rate, which is possible by designing or tuning the transmittance of the output coupler. We also rewrite the internal cooperativity by using typical cavity-QED experimental parameters, then it turns out that the single-photon generation efficiency is limited only by the one round trip cavity internal loss rate and the effective cavity mode area (normalized by the atomic absorption cross section). The bound is achieved in the limit that the variation of the system is sufficiently slow. We also examine more practical settings with short generation time. Moreover, repumping process, where the atom is repumped after its decay to the initial state, is also taken in to account. The effect becomes negligible when the cooperativity parameter is sufficiently high.

Jonathan Matthews

Quantum Engineering Technology Labs, School of Physics, HH Wills Physics Laboratory, University of Bristol, Bristol, UK

Silicon-based quantum photonic devices are rapidly growing in capability and complexity. This offers highly-multi-mode structures that coherently manipulate photonic quantum information with high fidelity. This technology is being used in quantum physics and quantum information experiments, and it is proposed as a means to realize large-scale quantum processors. We report a silicon photonics chip comprising 148 components, that we use to implement an arbitrary 2-qubit processor acting on photonic qubits. The ability to characterize such devices and measure quantum states within the photonic chip becomes increasingly important as the complexity of components increase further and as new component designs and capabilities are introduced. To contribute to these needs, we will report on-chip homodyne detectors with performance characteristics suitable for measurement of quantum states.

Karsten B. Dideriksen, Michael Zugenmaier, Anders S. Sørensen, Boris Albrecht, Eugene S. Polzik

Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen, DK-2100, Denmark

We work towards a heralded single-photon source based on the DLCZ protocol for quantum repeaters [1]. In this scheme, the detection of a photon scattered from an atomic ensemble heralds the creation of a collective atomic excitation. By applying a retrieval pulse, the collective excitation can be read out in the form of a single photon at a desired time. This herald-retrieve scheme has shown remarkable capability in cold ensembles, but the performance of warm ensembles has so far been hampered by dephasing due to atomic motion.

We present our latest results [2] of efficient heralding and readout of long-lived single collective excitations created in a caesium vapour. To extend the memory lifetime beyond the dephasing time induced by atomic motion, we implement the scheme proposed in ref. [3] where the atom-light coupling is averaged by atomic motion to create a collective excitation symmetrically shared by all atoms of the ensemble. We achieve a memory lifetime of 0.27(4) ms, a significant step towards timescales relevant for quantum repeater application. However, the fidelity of single-photon readout is compromised by an intrinsic four-wave-mixing noise process. We present our most recent endeavours in reducing four-wave mixing noise by proper choice of excitation scheme.

Lucas Lange, Frank Schäfer, Alexander Biewald, Richard Ciesielski, Achim Hartschuh

Department of Chemistry and Center for NanoScience (CeNS), LMU Munich, Germany

Single-photon emission is a hallmark of atom-like 0D quantum emitters, such as luminescent semiconductor nanocrystals, nitrogen vacancies in diamond and organic dye molecules[1]. In higher dimensional nanostructures, on the other hand, multiple spatially separated electronic excitations may exist giving rise to more than one emitted photon at a time [2]. We find that optical nanoantennas can be used to control the photon emission statistics of 1D nanostructures. Antenna-control exploits spatially confined near-field enhanced absorption and emission rates resulting in locally increased annihilation of mobile excitons and radiative recombination. As proof of concept, we experimentally demonstrate the reduction of the degree of antibunching in the photoluminescence of single carbon nanotubes using a metal tip. Our results indicate that, in addition to improving the performance of single photon sources [3], optical antennas have the potential to open up a broad range of materials for quantum information technology.

Valery Zwiller^1,3, J. Zichi^1,3, S. Gyger¹, A. W. Elshaari¹, L. Schweickert¹, K. D. Jöns¹, T. Lettner¹, K. D. Zeuner¹, E. Schön¹, A. Fognini³, I. Esmaeil Zadeh², S. Dobrovolskiy³, R. Gourgues³, J. W. N. Los³, G. Bulgarini³, S. Dorenbos³

¹Department of Applied Physics, KTH, Stockholm, Sweden
²Department of Optics, TU Delft, The Netherlands
³Single Quantum, Delft, The Netherlands

With the aim of realizing complex quantum networks, we develop quantum devices to generate quantum states of light with semiconductor quantum dots, single photon detectors based on superconducting nanowires and on-chip circuits based on waveguides to filter and route light.

The generation of single photons can readily be performed with single quantum dots. We demonstrate a very high single photon purity exceeding 99.99% generated at 795 nm [1], these quantum emitters also allow for interfacing with atomic ensembles. To enable long distance communication, we also develop quantum dot devices able to emit at telecom frequencies [2].

To allow for complex architectures, on-chip integration is required. We demonstrate filtering and routing of single photons with tunable ring resonators on a chip and discuss the scalability of this approach [3].

Generation and manipulation of quantum states of light would be useless without single photon detectors. We are therefore developing high-performance single photon detectors based on superconducting nanowires and will present state-of-the-art performance in terms of detection efficiency, low dark counts and time resolution [4].

Angelo Gulinatti, Francesco Ceccarelli, Giulia Acconcia, Massimo Ghioni, Ivan Rech

Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, piazza Leonardo da Vinci 32, 20133 Milano, Italy

The detection of single photons is an essential and critical step for the implementation of many quantum technologies.  Single-photon detectors are widely used today for example to implement and characterize sources of single/entangled photons or to perform fundamental experiments in linear optical quantum information processing (e.g. boson sampling, quantum gates, etc.). Requirements that are very demanding in terms of photon detection efficiency have made the Superconducting Nanowire Single-Photon Detector (SNSPD) the preferred choice for many of these applications. However, the SNSPDs are operated at cryogenic temperatures with obvious drawbacks in terms of cost, complexity and scalability.

Being operated at (close to) room temperature, silicon Single-Photon Avalanche Diodes (SPADs) represent an interesting alternative to make quantum technologies widely available and to bring them out of the lab. However, significant improvements are needed to meet their requirements.

We will present a technology for the fabrication of arrays of SPADs with high detection efficiency (up to 70% @600nm, 40% @800nm), low timing jitter (< 85ps FWHM) and capability of operating at high-count rates (dead-time down to 10ns). To demonstrate the potential of this technology we developed and fully characterized a detection module based on an array of 32x1 pixels.

Ivan Iakoupov, Yuichiro Matsuzaki, William J. Munro, Shiro Saito

NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan

Detecting single microwave photons is a very challenging task because of the much smaller energies associated with them compared to optical photons. Recently, there have been several theoretical proposals that can in principle operate in a continuous fashion: the detector (either an artificial atom or an auxiliary microwave cavity attached to it) is continuously probed, and one can both infer the presence of a photon and its arrival time. However, the figures of merit such as the measurement fidelity are usually calculated under the assumption that the photon arrival time is known. We show theoretically that in this case, the detector can be operated sequentially (that is the absorption of the microwave photon and the interrogation of the detector are separated in time) meaning a much better performance is achieved. In the idealized limit, the measurement fidelity can in-principle be arbitrarily close to 100%. This can be compared to the theoretical measurement fidelity reported for the continuous-mode detectors, where the best figure is 84% for one artificial atom and 96% for 4 artificial atoms. In conclusion, there is a price to be paid for the option of operating a microwave single-photon detector without the knowledge of the photon arrival time.

Christian Möller, Indira Käpplinger, Kristin Neckermann, Thomas Ortlepp

CiS Forschungsinstitut für Mikrosensorik GmbH, Konrad-Zuse-Straße 14, 99099 Erfurt, Germany

We demonstrate a flip-chip technology of a silicon carrier wafer with fiber-coupling and a superconducting nanowire single photon detector (SNSPD) for application in a closed cycle cryostat. The silicon carrier wafer enables a precise optical fiber holding via an inductive coupled plasma (ICP) etched hole. Further, the needed electrical contacts for the SNSPD are on the silicon chip. The goal is to investigate the thermal coupling between superconducting detector chip and closed-cycle cryostat as well as the flip- chip position accuracy of ± 1 µm between the two chips. The preliminary tests were done with silicon photodiodes instead of SNSPD chips.

Marek Burakowski¹, Wojciech Rudno-Rudziński¹, Anna Musiał¹, Grzegorz Sęk¹, Andrei Kors², Johann Peter Reithmaier², Mohamed Benyoucef²

¹Laboratory for Optical Spectroscopy of Nanostructures, Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, Wrocław, Poland
²Institute of Nanostructure Technologies and Analytics (INA), Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel, Heinrich-Plett-Str. 40, Kassel, Germany

In this contribution we experimentally determine fundamental magneto-optical properties of molecular beam epitaxy grown, symmetric and low-density InAs/InP quantum dots (QDs) emitting at the telecom C-band [1]. Polarization-resolved microphotoluminescence, also performed in magnetic field up to 5 T in Faraday configuration, indicates exciton fine structure splitting below the spectral resolution of the experimental setup (20 μeV). Measurements in Voigt configuration allow accessing dark exciton states and distinguishing between charged and neutral excitonic complexes. The exciton g‑factor and the diamagnetic coefficient are determined in Faraday configuration to be in the range of 0.7‑1.5 and 9‑12 μeV/T², accordingly, and consequently extension of the exciton wavefunction is in the range of 14‑18 nm, confirming the strong confinement regime. Derived parameters are important for modeling of the excitonic structure of the investigated dots.

Supported by the „Quantum dot-based indistinguishable and entangled photon sources at telecom wavelengths” project, carried out within the HOMING programme of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund. This work was also financially supported by the BMBF Projects German Federal Ministry of Education and Research (BMBF) (Q.com-H, Q.Link.X).

Rasmus Flaschmann¹, Fabian Flassig¹, Thomas Kainz¹, Lucio Zugliani¹, Rudolf Gross², Matthias Althammer², Jonathan Finley¹, Kai Müller¹

¹Walter Schottky Institut, Technische Universität München, 85748 Garching, Germany
²Walther-Meißner-Institut, Technische Universität München, 85748 Garching, Germany

In recent years, superconducting single photon detectors (SSPDs) have raised tremendous attention as a possible key technology for optical quantum information processing. Specifically, SSPDs promise the ability to detect single photons with a high efficiency, low dark count rate, fast response time and low timing jitter [1,2] and there is already a variety of detectors commercially available, mostly fiber-coupled system (e.g. Single Quantum, Scontel, …). However, those systems mainly rely either on a manual alignment of the detector to the fiber core or on a deep reactive ion etching (DRIE) process of the detector chip that allows the detector to be centered in a fiber mating sleeve [3,4]. Here, we present a novel approach to a self-aligning fiber-to-detector coupling mechanism that eliminates the necessity of DRIE and is suitable for arbitrary substrate/detector material combinations. Moreover, we present our recent progress on NbN and NbTiN SSPDs on SiO2.

Hristina Georgieva¹, Marco López¹, Beatrice Rodiek¹, Helmuth Hofer¹, Justus Christinck¹, Peter Schnauber², Arsenty Kaganskiy², Tobias Heindel², Sven Rodt², Stephan Reitzenstein², Stefan Kück¹

¹Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany
²Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstraße 36, D-10623 Berlin, Germany

The range of possible implementations of single-photon sources in quantum information processing is rapidly growing. In order to achieve high accuracy and metrological traceability, we need reliable methods for their absolute characterization. Bright single-photon sources having high purity combined with a narrow emission bandwidth are perfect candidates for a new quantum standard. In radiometry, such an absolute standard could be used for the detection efficiency calibration of single-photon detectors; therefore, it would enable the traceable measurement of optical power by counting photons. A suitable single-photon emitter that meets all these criteria is a single InGaAs quantum dot embedded in a deterministically fabricated microlens. We present a characterization of this source, which includes the measurement of photon count rate, spectral emission characteristics and second-order correlation function. The spectral filtering is realized by two bandpass filters, each having a full width at half maximum of 0.5 nm and a transmission of about 90 %. The emission peak with the highest intensity is selected by filter rotation to adjust the central wavelength of the transmission window. In contrast to the standard filtering method with a monochromator, our method reduces the photon losses, thus resulting in high count rates combined with high single-photon purity.

Matthew E. Trusheim¹, Benjamin Pingault², Noel H. Wan¹, Mustafa Gündoğan², Lorenzo De Santis¹, Kevin Chen¹, Mete Atatüre², Dirk Englund¹

¹Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA, USA
²Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom

Spin – photon interfaces are of central importance in quantum information science for potential quantum networking and distributed quantum computation applications. Long spin coherence times and high-quality single photon emission are required to realize solid-state nodes in quantum networks. Group IV (g-IV) colour centres have emerged recently as promising material systems that provide an optically-accessible spin together with narrow-linewidth, bright optical transitions. Through magneto-optical spectroscopy, we first verify that the electronic structure of SnV^- is similar to the other g-IV colour centres where phonon absorbtion is the main limitation to spin coherence times. We measure optical linewidths consistent with radiative lifetime limit. Lastly, we measure electronic spin lifetimes longer than the other g-IV colour centres, consistent with the larger ground state splitting. Our results indicate that SnV^- is a strong candidate for long-lived optical quantum nodes in a quantum network.

Pawel Holewa¹, Czcibor Ciostek¹, Pawel Wyborski¹, Christian Schneider², Elizaveta Semenova³, Marcin Syperek¹

¹OSN Lab, Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wyb. Wyspiańskiego 27, 50-470 Wrocław, Poland
²Technische Physik & Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
³DTU Fotonik, Technical University of Denmark, Kongens Lyngby, DK-2800, Denmark

Here we present optical properties of low-surface density (109-1010 cm-2) InAs/InP self-assembled quantum dots grown by MOVPE. The QDs ensemble emission exhibits multimodal characteristics and covers broad spectral range from 1.3 to 1.9 µm at T=10K. The photoluminescence (PL) excitation experiments at T=10K show that the dots are settled on a 4 ML-thick wetting layer defined by the 2D energy gap of ~1 eV. The Atomic Force Microscopy images unveiled large sizes of surface QDs (10-13 nm in height and 60-80 nm at the base) and small in-plane aspect ratio of 1.1-1.3. However, the observed broad multimodal emission suggests that buried QDs can be significantly reduced in size. This hypothesis is additionally confirmed by the calculations of the energy band structures using the 8 band kp method.

Finally, the planar QD structure is processed by the e-beam lithography and chemical and dry etching to prepare mesa structures. High spatially-resolved PL experiments show well spectrally-resolved single emission lines attributed to excitonic complexes recombination processes in single InAs/InP QDs. Strong PL signal, registered especially between 1.5 and 1.61 µm serves as a base for further research towards the efficient and low fabrication cost of single or entangled photon sources at telecom.

Jakub Jasiński¹, Nicole Srocka², Wojciech Rudno-Rudziński¹, Philipp-Immanuel Schneider³, Sven Burger^3,4, David Quandt², Andre Strittmatter², Sven Rodt², Anna Musiał¹, Stephan Reitzenstein², Grzegorz Sęk¹

¹OSN Laboratory, Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
²Institute of Solid State Physics, Technical University of Berlin, Hardenbergstraße 36, D-10623 Berlin, Germany
³JCMwave GmbH, Bolivarallee 22, D – 14050 Berlin, Germany
⁴Zuse Institute Berlin, Takustraße 7, D – 14195 Berlin, Germany

            Enhancing the extraction efficiency of non-classical light sources is crucial for the implementation of many quantum communication protocols, e.g., Quantum Key Distribution. While high values have been obtained for sub-micrometer wavelengths (>70%, [1],[2]), in the telecommunication range at maximum 36% has been achieved for 1.3μm, but only in a non-deterministic narrow-band cavity approach [3].

In order to achieve higher and spectrally broad extraction efficiencies a more robust system of In0.75Ga0.25As/GaAs quantum dots (QDs) capped with an In0.2Ga0.8As strain reducing layer were grown on a distributed Bragg reflector, and selected single dots were deterministically embedded in mesas using low-temperature in-situ electron beam lithography [4], [5]. The extraction efficiency of the source has been determined based on the single QD emission spectrum measured in the calibrated setup under non-resonant pulsed excitation using superconducting nanowire single-photon detectors. The origin of the respective emission lines has been identified by means of power-dependent and polarisation-resolved microphotoluminescence measurements.

Preliminarily, an extraction efficiency of 10% has been achieved [5], which could be significantly increased for the structures fabricated following a numerical optimization of the mesa geometry indicating an achievable extraction efficiency of 40%. That shows a potential for surpassing values demonstrated so far for the telecommunication range.

Paul Kaufmann, Helen Chrzanowski, Sven Ramelow

Humboldt-Universität zu Berlin, Institut für Physik

Various materials, such as plastics, gases or tissue, have strong and distinct spectral absorption features in the mid-IR wavelength regime by which they can be identified. These are the consequence of molecular vibrational transitions. However, this technologically very important wavelength regime between 3-10µm - commonly also called the fingerprint region - has some fundamental limitations mainly related to the large noise in mid-IR detectors and the complexity and cost of bright, broadband mid-IR light sources
By using quantum-correlated photon pairs from spontaneous parametric downconversion (SPDC) generated in a non-linear interferometer, we can circumvent these limitations: the mid-IR idler photons can probe the sample while we can extract the spectrum via the signal light (around 800nm) with high resolution and efficiency using a cost-effective, uncooled and off-the-shelf grating spectrometer. We are developing this highly non-invasive and potentially fast and cost-effective method and investigate its potential for real-world applications replacing standard-techniques like Fourier transform infrared spectroscopy (FTIR). Here we present first experimental results for polymer analysis and gas spectroscopy.

Sanjukta Kundu, Wiktor Szadowiak, Jerzy Szuniewicz and Radek Łapkiewicz

Division of Optics, Faculty of Physics, University of Warsaw. ul. Pasteura 5, Warsaw, 02-093

Complete characterization of spatial structure of single photons is essential for free space quantum optical communication and for the efficient extraction of information from light in quantum imaging. We introduce and experimentally demonstrate an interferometric technique which enables complete characterization of a two-dimensional spatial structure (amplitude and phase) of a single photon. Importantly, instead of using a known reference photon to achieve the goal, our technique relies on the fact that a single photon can interfere with itself. Our setup comprises of a heralded single photon source with an unknown spatial phase and a modified Mach-Zehnder interferometer with a spatial filter in one of its arms. We experimentally confirm the feasibility of our technique for heralded single photons, by reconstructing their spatial phase structure from the measurement of lowest order interference fringes. The technique can be applied to characterize arbitrary spatial states of single photons (e.g. orbital angular momentum modes). We believe that because of its simplicity, our measurement scheme might find multiple applications in the fields of quantum imaging and quantum communication.

Timm Kupko¹, Lucas Rickert¹, Martin von Helversen¹, Alexander Schlehahn¹, Sven Rodt¹, Christian Schneider², Sven Höfling^2,3, Stephan Reitzenstein¹, Tobias Heindel^1,*

¹Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin, Germany
²Technische Physik, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
³SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, United Kingdom
^*e-mail: tobias.heindel@tu-berlin.de

Solid-state single-photon sources have the potential to boost the performance of quantum-key-distribution (QKD) systems [1]. First proof-of-principle experiments affirmed these prospects of quantum-light sources [2-4], but further efforts are necessary to push this field to practical applications. In this contribution, we will present our recent progress in the development of practical devices for quantum communication. The first device is a plug-and-play single-photon source (SPS) based on semiconductor quantum dots. Here, a compact Stirling cryocooler is employed as basis for user-friendly operation of our SPSs at cryogenic temperatures [5]. In this context, the efficient direct coupling of electrically operable quantum light sources to optical single-mode fibers is addressed, representing one crucial step towards applications. The second device constitutes a receiver module designed for polarization-encoded QKD. We show that temporal filtering of single-photon pulses can be used for a performance optimization of QKD systems implemented with realistic quantum-light sources. Finally we demonstrate, real-time security monitoring using our receiver-module by evaluating g(2)(0) inside the quantum channel. The results presented here are an important contribution towards the development of QKD-secured communication networks based on quantum-light sources.

Inna Kviatkovsky^1,2, Helen Chrzanowski^1,2, Sven Ramelow^1,2

¹Institute of Physics, Humboldt University, Berlin.
²Integrative Research Institute for the Sciences, IRIS Adlershof, Berlin

Mid infrared (mid-IR) light is highly relevant for both technology and basic research. Currently, detection in the mid-IR is greatly compromised due to the poor temporal and spatial resolution of the IR detectors available in the market. We demonstrate a quantum imaging concept that allows sensing in the mid-IR while detecting in the visible. By pumping a nonlinear crystal with laser light, we generate photon pairs via spontaneous parametric down conversion (SPDC). One photon of the pair is in the mid-IR range and is probing the sample, the second photon is in the visible range to be later detected. The photon pairs and the laser pump light are then recombined in a second crystal and the mid-IR information about the sample is transferred through coherence and manifested in nonlinear interference of the visible light. This allows sensing in the mid-IR while detecting in the visible with a standard CMOS camera, enabling low noise, low cost and fast data acquisition. Implementing mid-IR quantum imaging will not only open up an entirely new wavelength regime for single photon quantum optics but also be practically useful for real world applications in various fields. 

Swagata Bhunia¹, Ritam Sarkar², Suddhasatta Mahapatra¹, Apurba Laha²

¹Department of Physics, Indian Institute of Technology Bombay, Mumbai-400076, India
²Department of Electrical Engineering, Indian Institute of Technology Bombay, Mumbai-400076, India

On-demand single photon emission is a fascinating proposition rendered by the theorists. However, it has been a great challenge to the experimentalists to realize a device that truly delivers a single photon as and when required, in particular at the higher temperature (~300K). Notwithstanding the formidable challenge, there has been an unprecedented volume of research that has been growing exponentially during the last two decades in this area [1-3].

In this work we report growth and characterization of three-dimensionally confined III-Nitride (GaN) quantum dots towards designing a single photon source. The unique approach/process that we have devised in this work, enables us positioning the quantum dot at the desired location. Unlike all the recent reports where GaN quantum dots/disc which primarily shows dimensional confinement in only one direction, our approach comprises of positioning 3-D confined GaN quantum dots within AlN which is grown on GaN and/or AlGaN quantum wire template. Room temperature photoluminescence measurements from these quantum dots show a blue shift of >150meV, confirming quantum confinement at room temperature. Our process begins with the growth of III-Nitride nanowires using plasma-assisted molecular beam epitaxy (PAMBE) technique on the sapphire substrate followed by transforming them into quantum wires which eventually act the virtual substrate/template for growing GaN quantum dots. We believe that these quantum dots could be an ideal source for single photon emission at higher (~300K). Measurements of photon statistics (Hanbury-Brown Twiss (HBT) setup) from these QDs are in progress and will be reported later.

Pei-Yi Lin

peiyi@singlequantum.com

Light detectors are crucial components of optical imaging and telecommunication systems. The ultimate photon detector is capable of detecting even an elementary particle of light, a single photon.

We develop the best single photon detectors, based on superconducting nanowires. The SNSPDs are provided with closed-cycle cryostat, which provides the low temperature environment for the superconducting nanowires. The high performance of our SNSPDs makes them the ideal choice for the most demanding applications.

Felix Mann

Humboldt-Universität zu Berlin, Institut für Physik, Emmy Noether-Gruppe Nichtlineare Quantenoptik, Newtonstraße 15, DE-12489 Berlin

Satellite-based free space quantum key distribution is a promising approach for the next generation of secure communication [1]. It typically operates in the infrared atmospheric window between 800-900 nm. In this rage also caesium-based quantum memory is being developed as the basis for a quantum-repeater network. An essential building block is a lightweight, narrowband and bright entangled photon source at ceasium D1 wavelength.

This project aims at the generation of time-energy entangled photon pairs (one at 894 nm) using spontaneous four-wave mixing (SFWM) in a silicon nitride microring resonator. This nonlinear parametric process convertes two pump photons into one signal and one idler photon [2].

In a first step the spectral properties of the rings were measured and a suitable ring was chosen, that for a specific pump wavelength, will generate photons at excactly the D1 Cs line. After separating the photon pairs and suppressing the pump light, measuring the cross-correlation will verify and temporally characterize the generation of the photon pairs. In a last step, entanglement will be verified using a Franson interferometer.

Amur Margaryan, for RF Timer collaboration

Yerevan Physics Institute, 2 Alikhanyan Bros. Str., 0036 Yerevan, Armenia

A dedicated helical deflector to perform circular and spiral sweeps of keV electrons by means of radio frequency fields in a frequency range of 500-1000 MHz is considered. By converting the time dependence of incident electrons to a hit position dependence on a circle or spiral, this device can potentially serve as an ultra-fast and ultra-precise timing processor. Results of current theoretical and experimental studies will be presented. Possible applications in an ultra-fast and ultra-precise single photon detectors will be discussed.

Monika Mikulicz¹, Kinga Żołnacz², Nicole Srocka³, Jan Große³, Wacław Urbańczyk², Sven Rodt³, Anna Musiał¹, Stephan Reitzenstein³, Grzegorz Sęk¹

¹OSN Laboratory, Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, 50370 Wrocław, Poland
²Department of Optics and Photonics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, 50370 Wrocław, Poland
³Institute of Solid State Physics, Technical University of Berlin, 10623 Berlin, Germany

Hereby, we report on the photoluminescence (PL) study of MOCVD-grown strain-engineered In0.75Ga0.25As/In0.2Ga0.8As/GaAs quantum dots (QDs) measured at temperature of 40K in a Stirling cryocooler and with direct optical fiber coupling of excitation and detection. Cryogenic-free cooling is cheap, compact and easy in operation method in comparison to He-flow or closed-cycle cryostats typically used in single QD experiments, but the limitations are higher minimal working temperature (>28K) and intrinsic vibrations. Therefore, we propose a solution with optical coupling based on fiber in a ferrule glued directly to a single QD-mesa. The alignment procedure is based on the interference of light back-reflected from the top surface of the sample and the end facet of the fiber as a feedback signal to locate the center of the mesa, because adjustment for the QD emission is not possible at room temperature [1]. The QD itself is located in the mesa center provided by means of in-situ electron-beam lithography [2]. We demonstrate single QD emission at wavelengths above 1.2 μm from a single fiber-coupled GaAs-based quantum dot-mesa in a compact Stirling cryocooler and relative standard deviation of the PL intensity over 10 cooling cycles equal to 5.7% proving repeatability and durability of the proposed approach.

Laura Orphal¹, Joseph H. D. Munns¹, Tim Schröder^1,2

¹Institut für Physik, Humboldt-Universität zu Berlin, Berlin, Germany
²Ferdinand-Braun-Institut, Berlin, Germany

The efficient entanglement of stationary qubits in quantum communication systems is based on coherent photons. For their generation lifetime-limited emission linewidths are a fundamental requirement.

Particularly for the nitrogen-vacancy (NV) centre in diamond, natural linewidths (~13 MHz) are challenging to achieve. In addition to homogeneous broadening, particularly, spectral diffusion, i.e., the change of optical transition frequency over time, caused by fluctuations of the electrostatic environment, leads to inhomogeneous broadening of the zero-phonon line (ZPL).

To suppress spectral diffusion, work is done on optimizing nanofabrication methods. Another interesting alternative are active control schemes. Recently the approach of pulsed coherent control was proposed, which relies on the fact that the frequency of an emitted photon is determined by the average rate of phase accumulation between the states of a solid-state emitter over the spontaneous emission time [1]. Applying a sequence of optical π-pulses to the emitter modifies the phase between the involved states and consequently the emission spectrum. In this way the ZPL can be stabilized at a chosen frequency given by the carrier frequency of the pulses.

Here, we present our work towards experimentally implementing the protocol for reducing spectral diffusion of the ZPL of NV defect centres with optical pulses.

Tobias Simmet¹, William Rauhaus¹, Friedrich Sbresny¹, Malte Kremser¹, Fuxiang Li², Nikolai Sinitsyn², Kai Müller¹, Jonathan J. Finley¹

¹Walter Schottky Institut, Technische Universität München (Germany)
²Los Alamos National Laboratory (USA)

Single spins confined to semiconductor quantum dots are promising candidates for highly efficient spin-photon interfaces. To these ends, we investigate the dynamics of single electron and hole spins confined to self-assembled InAs quantum dots through time-domain measurements [1-2]. For electron spins, we observe fast ensemble dephasing (~2ns), slow spin relaxation due to nuclear spin co-flips with the central spin (>1µs) and at intermediate timescales (~750ns) an additional stage which is attributed to the quadrupolar coupling of the nuclear spins to strain-induced electric field gradients [1]. In contrast, for hole spins we observe more than two orders of magnitude slower dephasing due to the reduced hyperfine interaction resulting from their p-like Bloch function [2]. Moreover, for hole spins we observe a decrease of T₂* with increasing magnetic field which we attribute to the sensitivity of the hole-g factor to electric field noise.

Houssaine Machhadani¹, Raouia Rhazi^1,2, Julien Zichi³, Catherine Bougerol⁴, Stéphane Lequien⁵, Guillaume Rodriguez⁶, Richard Souil⁶Jean-Luc Thomassin¹, Nicolas Mollard⁵, Val Zwiller³, Ségolène Olivier², Jean-Michel Gérard¹

¹Univ. Grenoble-Alpes, CEA-IRIG, PHELIQS, 17 av. des Martyrs, 38000 Grenoble, France
²Univ. Grenoble-Alpes, CEA-LETI, DOPT, 17 av. des Martyrs, 38000 Grenoble, France
³KTH Stockholm, Department of Applied Physics, SE-114, 128 Stockholm, Sweden
⁴Univ. Grenoble-Alpes, CNRS-Institut Néel, 25 av. des Martyrs, 38000 Grenoble, France
⁵Univ. Grenoble-Alpes, CEA-IRIG, MEM, 17 av. des Martyrs, 38000 Grenoble, France
⁶Univ. Grenoble-Alpes, CEA-LETI, DPFT, 17 av. des Martyrs, 38000 Grenoble, France

Superconducting-nanowire single-photon detectors (SNSPDs) have demonstrated their capacity to outperform avalanche diodes in terms of efficiency and reduced jitter. Today, Nb(Ti)N is a widely used material for the SNSPD technology. The use of III-nitride semiconductors as buffer layer for Nb(Ti)N presents interesting advantages, since GaN and AlN are almost lattice matched with NbN, and they are transparent to visible and near-IR radiation. In this work, we study the impact of a crystalline III-nitride (GaN or AlN) buffer layer on the properties of ultrathin films of NbTiN deposited by reactive magnetron sputtering [1]. Best results are obtained using crystalline AlN, which leads to NbTiN with a superconducting critical temperature Tc = 11.8 K, and sharp superconducting transition (T = 0.83 K). This is major improvement in comparison with NbTiN deposited on SiO2 on Si (Tc = 9.8±0.3 K with T ≈ 0.87). The first superconducting nanowire single photon detectors on crystalline AlN have been demonstrated [1]. Elaborating on these results, we are exploring the replacement of crystalline AlN by thin AlN layers deposited by DC magnetron sputtering on 8” silicon substrates. Such an approach would allow performance improvement of SNSPD on Silicon.

Beatrice Rodiek, Justus Christinck, Helmuth Hofer, Hristina Georgieva, Marco López, Stefan Kück

Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany

Single-photon sources have a wide field of implementation, e.g. in quantum key distribution, quantum computing, and quantum-enhanced optical measurements. Because of their negligible background and high suppression of multi-photon emission, single-photon sources have the potential to become a standard source in radiometry. Such source is necessary to close the gap between classical and quantum radiometry. The metrological realization of a room temperature absolute single-photon source based on a nitrogen-vacancy (NV-) center in nanodiamond was already carried out by the Physikalisch-Technische Bundesanstalt (PTB) via an unbroken traceability chain to the national standards [1].

In order to improve the understanding of the emission characteristics, we investigated the angular emission behavior of NV-centers in nanodiamonds. These NV-centers in nanodiamonds are located in the vicinity of a dielectric structure, namely a microscope cover glass. We will present the development of a model [2] of the angular distribution of the emitted light. The angular dependent emission of NV-centers is measured by back focal plane imaging. Furthermore, the theoretical simulations of the radiation patterns are compared with the measurement of the angle dependent emission. The results will be shown at the symposium.

Hanna Salamon¹, Aleksander Maryński¹, Paweł Wyborski¹, Anna Musiał¹, Artem Bercha², Witold Trzeciakowski², Tobias Heuser³, Nicole Srocka³, David Quandt³, André Strittmatter³, Sven Rodt³, Paweł Podemski¹, Stephan Reitzenstein³, Grzegorz Sęk¹

¹Laboratory for Optical Spectroscopy of Nanostructures, Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology, Poland
²Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw, Poland
³Institute of Solid State Physics, Technical University of Berlin, Berlin, Germany

High-resolution photoluminescence excitation spectroscopy (μPLE) is a powerful method for energy structure characterization of single quantum dots (QDs). Despite its advantages it becomes very challenging beyond 1 μm as it requires narrow-linewidth tunable laser in the adequate spectral range. We have developed a dedicated μPLE setup optimized for the telecom range with set of special filters and continuous wave, tunable (1210 - 1310 nm), self-made, external cavity laser in Littman configuration. The measurements were performed in order to identify higher energy states in the individual QDs, which can be further utilized for the efficient quasi-resonant excitation to obtain purified single QD and in particular single-photon emission.  

We investigated epitaxial InGaAs/GaAs QDs with additional strain reducing layer to obtain emission in the telecommunication O-band [1] suitable for non-classical light generation and short-distance quantum communication in fiber networks [2]. μPLE results revealed s-p splitting in such dots in the range of 70 meV in agreement with PL data on the QD ensemble [3]. Its dependence on the emission energy (supported with 8 band k.p calculations combined with the configuration interaction approach [4]) indicates on significant changes of the In content within QDs of different size as a factor determining the emission energy.

Philip Thomas, Matthias Körber, Olivier Morin, Stefan Langenfeld, Gerhard Rempe

Max-Planck-Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching, Germany

Many quantum communication protocols rely on the faithful storage of quantum bits. Here, we present a qubit memory based on a single 87Rb atom dipole-trapped in a high-finesse optical resonator and capable of storing and retrieving single-photon polarization qubits with an overall efficiency above 20% when probed with highly attenuated coherent laser pulses containing one photon on average. Based on seminal work [1], the polarization of the photon is mapped onto a pair of states with opposite spin quantum numbers. These two atomic levels experience an opposite Zeeman shift which constitutes the main source of decoherence in the presence of magnetic field fluctuations. This limits the coherence time to a few hundred microseconds. By temporarily mapping the qubit to a decoherence-protected subspace, we extend the coherence time of the memory to more than ten milliseconds. Now, the coherence time is no longer limited by magnetic field noise, but by trap-induced differential light shifts of the new qubit basis states. We can overcome this effect by application of a spin-echo technique, which improves the coherence time to more than 100 milliseconds. Our results are an important milestone towards the realization of long-distance quantum communication.

Max Tillmann¹, Michael Wahl¹, Tino Röhlicke¹, Andreas Bülter¹, Doreen Wernicke², Martin Wolff³, Matthias Häußler³, Nicolai Walter³, Robin Stegmüller³, Fabian Beutel³, Wolfram Pernice³, Carsten Schuck³, Nicolas Perlot⁵

¹PicoQuant GmbH, Rudower Chaussee 29, 12489 Berlin
²Entropy GmbH, Gmunder Str. 37a, 81379 München
³WWU Münster, Physikalisches Institut, CeNTech II, Heisenbergstr. 11, 48149 Münster
⁴Fraunhofer Heinrich-Hertz Institute, Einsteinufer 37, 10587 Berlin

Single photons are ideal information carriers in many classical and quantum applications. One of the key challenges in transferring these applications from a laboratory environment ‘into the field’ are the limited count rates achievable with today's hardware. Individual photon detection units – comprised of a single detector element and and its timing electronic – run against a physical limit if photons impinge too rapidly.

It is the scope of this project to develop key enabling components to push beyond the bandwidth-limit of single devices with a massively parallelized (x64) single-photon detection system. To this end, detector elements based on superconducting nanowires are optimized for lowest reset times and highest temporal resolution. Care is taken that the optical and electrical interfacing does not degrade the detection performance. To process the high data rates generated with such a system, the readout electronics need to be parallelized in a similar fashion. In particular, an on-chip (FPGA) data processing over all detector channels provides a viable solution to pre-process the initial data such that it can be transferred to a host computer via limited bandwidth links. Ultimately, the performance of this detection system will be evaluated in an applied scenario via a suitable QKD-scheme.

Yanhua Wang^1,3, Ke Zhang², Hongying Yang², Aixian Li², Nan Zhao²

¹School of Physics and Electronic engineering, Shanxi University,Taiyuan,Shanxi,030006 ,China
²Beijing Computational Science Research Center, Beijing, 100193, China
³State Key Laboratory of Quantum Optics and Quantum Optics Devices，Shanxi University, Taiyuan Shanxi 030006, China

Accurate rotation sensors are highly demanded in both industrial applications and academic researches. We demonstrate an optical readout for rotation information by virtue of the light absorption of alkali-metal vapor cells. A rotational quarter-wave plate, mounted on the under test object co-axially, modifies the polarization state of a linearly polarized incident laser beam. Because that the atomic population among ground-state and spin polarization depend on the polarization of the incident laser due to the pumping process,  the transmission intensity of the laser beam or the the absorption coefficient of the vapor cell，which represent the optical pumping effect of alkali atoms，are related to the angular displacement of the under test object.Then the angular displacement of the object is converted to the changing the polarization state of laser and the rotation is converted to the intensity of laser passing through the vapor cell.  The information of angular velocity and angular acceleration can also be extracted from the angular displacement,certainly.The angular displacement sensitivity is  $2times10^{-5}{}^{circ}/sqrt{rm Hz}$ without magnetic shield.Our work make a way to optical rotation sensors with high-accuracy, compactness and low cost using atomic vapor cells.