Antibunching

Reveal Single-Photon Emission through g² Analysis

A quantum optical signature revealed by time-resolved photon correlation analysis to identify single-photon emission in materials and nanostructures.
Schematic comparison of antibunched, bunched and coherent photon emission statistics
Table of contents

Single-Photon Emission and Correlation Analysis

What is Antibunching?

Antibunching describes a non-classical property of light where photons are emitted one at a time rather than in groups. It is characterized by a reduced probability of detecting two photons simultaneously, typically expressed by the second-order correlation function indicating g²(0) < 1. Antibunching is a defining signature of single-photon emission and cannot be explained by classical light models. It is commonly observed in quantum emitters such as single molecules, quantum dots, color centers, or defects in solids, and plays a central role in quantum information processing and material characterization.

Scheme illustrating the setup and principle of antibunching measurements. Photon arrival times are recorded on two detection channels and correlated to obtain the second-order correlation function g²(τ), revealing the characteristic antibunching dip at zero lag time.

How does Antibunching measurement work?

Antibunching measurements are performed using time-resolved photon correlation techniques. Emitted photons are split into two detection paths and usually recorded with single-photon detectors in a Hanbury Brown and Twiss (HBT) configuration. By correlating photon arrival times, the second-order intensity correlation function g²(τ) is calculated. A pronounced dip at zero time delay indicates suppressed simultaneous emission and thus antibunching. Time-correlated single-photon counting (TCSPC) enables picosecond resolution, allowing antibunching to be resolved even for fast emitters and high repetition-rate excitation.

Antibunching Data & Analysis

Antibunching data are typically represented as a second-order correlation histogram g²(τ), showing coincidence counts as a function of time delay following a multi-start multi-stop principle. Quantitative analysis focuses on the value of g²(0), which indicates the degree of single-photon purity, as well as on the shape of the correlation curve. Background correction, detector timing jitter, and afterpulsing effects must be accounted for to avoid false antibunching signatures. Fitting models may include lifetime information, multi-level emitter dynamics or bunching contributions at longer delays, providing insight into emitter kinetics, population dynamics, and environmental interactions.

PicoQuant software for Antibunching analysis

PicoQuant software supports flexible coincidence correlation analysis via UniHarp and snAPI as well as quantitative evaluation of g²(τ) data for antibunching studies via QuCoa.

Why use Antibunching?

Antibunching measurements provide a direct and unambiguous test for single-photon emission. They are essential for identifying and validating quantum emitters, assessing photon purity, and distinguishing quantum light sources from classical or multi-emitter systems. In materials science, antibunching enables the study of defects, nanostructures, and low-dimensional materials at the single-emitter level. In quantum optics, it is fundamental to applications in quantum communication, quantum computing, and photon source characterization, even stretching towards novel imaging and microscopy techniques.

Instrumentation suited for antibunching measurements, including PMA Hybrid Series, PDM Series and PicoHarp 330.

Instrumentation requirements for Antibunching

Reliable antibunching measurements require fast single-photon detectors with low timing jitter, low dark counts, and minimal afterpulsing. Time tagging electronics with high temporal resolution are essential for accurate correlation analysis. Stable pulsed or continuous-wave excitation sources are needed, depending on the emitter dynamics and excitation scheme. Multi-channel data throughput and precise timing synchronization are critical, especially at high count rates. Dedicated acquisition and analysis software is required to compute correlation functions, apply corrections, and extract quantitative g² values.

Relevant for Your Research​

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Application Examples

The following examples illustrate how antibunching measurements are applied to verify single-photon emission from solid-state quantum emitters and individual fluorescent molecules under controlled experimental conditions.

Coincidence correlation showing photon antibunching of NV centers in nanodiamonds

Nitrogen Vacancy (NV) Centers in Diamond

Nitrogen vacancy centers in diamond are well-established solid-state single-photon emitters with exceptional photostability and biocompatibility. Using the MicroTime 200 with 532 nm excitation and detection between 600–800 nm, FLIM imaging confirmed stable emission from sub-10 nm nanocrystals. Subsequent antibunching measurements revealed a pronounced g²(0) dip, demonstrating single-emitter behavior and validating their suitability for quantum optics, nanophotonics, and bioimaging applications.

PicoHarp TCSPC g2 correlation trace showing antibunching of Atto 655

Antibunching of Atto 655

Antibunching measurements of a highly diluted Atto 655 solution (0.1 nM) were performed using the MicroTime 200 with pulsed excitation at 635 nm. Detection in a standard Hanbury Brown and Twiss configuration and TCSPC analysis revealed a reduced correlation peak around 95 ns, confirming single-molecule emission behavior.

Related Methods

Schematic of coincidence correlation showing Δt and g²(τ) antibunching dip

Coincidence Correlation

A time-resolved photon correlation technique that analyzes coincidence events between detection channels to quantify photon statistics. Antibunching measurements represent a specific application of coincidence correlation focused on identifying non-classical light emission.

In-Depth Scientific Resources

Premium Resources

Access in-depth application notes and scientific posters with detailed methods, measurement data, and real-world use cases.

Poster: High Spatial Photoluminescence Investigation of Nanostructures

Poster on high-spatial photoluminescence studies of nanostructures and quantum emitters using time-resolved confocal microscopy and spectroscopy.

Poster: Next Generation TCSPC Detection

Poster on next-generation TCSPC detection using PMA Hybrid detectors, enabling artifact-free FCS, antibunching measurements, and high-sensitivity FLIM imaging.

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