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Quantum Optics

Quantum Communication

Quantum mechanics guarantee secure communication

Quantum communication is a field of applied quantum physics closely related to quantum information processing and quantum teleportation. Its most interesting application is protecting information channels against eavesdropping by means of quantum cryptography. The most well known and developed application of quantum cryptography is quantum key distribution (QKD). QKD describes the use of quantum mechanical effects to perform cryptographic tasks or to break cryptographic systems. The principle of operation of a QKD system is quite straightforward: two parties (Alice and Bob) use single photons that are randomly polarized to states representing ones and zeroes to transmit a series of random number sequences that are used as keys in cryptographic communications. Both stations are linked together with a quantum channel and a classical channel. Alice generates a random stream of qubits that are sent over the quantum channel. Upon reception of the stream Bob and Alice — using the classical channel — perform classical operations to check if an eavesdroper has tried to extract information on the qubits stream. The presence of an eavesdropper is revealed by the imperfect correlation between the two lists of bits obtained after the transmission of qubits between the emitter and the receiver. One important component of virtually all proper encryption schemes is true randomnessm which can elegantly be generated by means of quantum optics.

Quantum Key Distribution (QKD)In a typical QKD setup, the photons are generated by a single photon source, encoded into binary values (i.e. representing "0" and "1") and then transmitted to the receiver either via optical fibres or in free space. The receiver then decodes the state of photons and detects them using single photon sensitive detectors and time-tagging electronics. There are several methods for encoding and decoding the photons:

  • via polarization: the binary information "1" or "0" is defined by the polarization of the single photons, e.g. binary "0" correlates with the horizontally polarized photon and binary "1" with vertically polarized photon
  • via the phase, which requires the use of a interferometer system: the phase difference Δφ = φAlice - φBob of the two interferometers is then used for encoding the binary values, e.g. a phase difference Δφ=0 correlates with the binary "0" and the phase difference Δφ=π correlates with the binary "1"
  • via entangled photons, which requires one sender of entangled photon pairs and two receivers (Alice and Bob) each equipped with a polarizer.  Alice and Bob set the two angles at their respective polarization rotator randomly. If the angles of Alice and Bob match, both photons behave exactly the same at the beam splitter, i.e. they are either transmitted (binary "1") or reflected (binary "0").

PicoQuant offers several instruments such as time-tagging units and single photon sensitive detectors that can be used to build a quantum key distribution system:

Time-tagging Units

HydraHarp 400 - multichannel time tagging moduleHydraHarp 400

Multichannel Picosecond Event Timer

  • Up to 8 independent input channels and common synch channel (up to 150 MHz)
  • Time channel width of 1 ps
  • Time tagging with sustained count rates up to 40 Mcps
  • USB 3.0 connection

PicoHarp300 - time tagging unitPicoHarp 300

Compact Dual-Channel Picosecond Event Timer

  • Two identical synchronized but independent input channels
  • Time channel width of 4 ps
  • Time tagging with sustained count rates up to 5 Mcps
  • USB 2.0 connection

TimeHarp260 - time tagging moduleTimeHarp 260

Dead-time Free Coincidence Correlation

  • One or two independent input channels and common synch channel (up to 84 MHz)
  • Two models with either 25 ps (PICO model) or 1 ns (NANO model) base resolution
  • Ultra short dead time (< 25 ns for PICO model, < 1 ns for NANO model)
  • PCIe interface

Single Photon Detectors

PDM SPAD - single photon sensitive detectorPDM Series

Single Photon Avalanche Diodes

  • Timing resolution down to < 50 ps (FWHM)
  • Detection efficiency up to 49%
  • Different active areas: 20, 50, and 100 µm
  • Ultra stable at high count rates

Random Number Generators


Quantum Random Number Generator

  • Quantum Random Number Generator based on photon arrival times
  • Bit rate: 150 Mbits/s
  • Interface: USB 2.0

Latest 10 publications related to Quantum Communication

The following list is an extract of 10 recent publications from our bibliography that either bear reference or are releated to this application and our products in some way. Do you miss your publication? If yes, we will be happy to include it in our bibliography. Please send an e-mail to info@picoquant.com containing the appropriate citation. Thank you very much in advance for your kind co-operation.