Applications of Photon Counting Techniques: Multi-Photon Interference and Entanglement

Yiqi Song, Meixue Chen, Yuhan Ma +7 more

The Hanbury Brown–Twiss (HBT) interferometer, which is used to measure the correlation of two photons or two light beams, has played a crucial role in quantum optics and quantum information. We propose a generalized HBT interferometer, which is able to measure the correlation of photons or light beams up to eight in a single experimental run. With an improved time correlated single-photon counting (TCSPC) algorithm, two-, three-, and four-photon coincidence counts, and the degree of fifth-order coherence of pseudothermal light are measured with a data collection time of 60 s. The generalized HBT interferometer can be used to measure the correlation of two multi-photon detection events by simulating photon number resolving detectors with multiple single-photon detectors. The generalized HBT interferometer and improved TCSPC algorithm provide a versatile framework for studying multi-photon correlations and interference, which is helpful to understand the physics of multi-photon interference and may find applications in fluorescence lifetime imaging and other techniques using TCSPC.

I. N. Agafonov, Maria V. Chekhova, T. Sh. Iskhakov

We consider possible ways to recognize multi-photon entangled states in experiment. A commonly used technique is to measure higher-order multi-photon correlation functions and their dependence on certain phase delays (multi-photon interference). Theoretically and experimentally, we show that multi-photon interference can have very high visibility for classical sources: up to 81.8% in the three-photon case and up to 94.4% in the four-photon one. Therefore, the visibility of multi-photon interference should not be used as a criterion of multi-photon entangled states generation. Instead, we suggest to characterize multi-photon entanglement by the photon-number dependence of the normalized correlation functions.

Z. Y. Ou

Giuliano Scarcelli, Alejandra Valencia, Yanhua H. Shih

Thermal (or pseudothermal) radiation has been recently proposed for imaging and interference types of experiments to simulate entangled states. We report an experimental study on the momentum correlation properties of a pseudothermal field in the photon counting regime. The characterization and understanding of such a light source in the context of two-photon physics, especially its similarities and differences compared to entangled two-photon states, is useful in gaining knowledge of entanglement and may help us to assess the real potential of applications of chaotic light in this context.