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Quantum Communications and Quantum Imaging

Efficient generation of photon bunched light for clock synchronization

Darren Ming Zhi Koh, Justin Yu Xiang Peh, Zifang Xu, Xi Jie Yeo, Christian Kurtsiefer, Peng Kian Tan

Published Jul 31, 2025• 0 citations
Publisher

Abstract

Photon bunching is the phenomenon in which photons in a light field have a higher than random probability of being grouped together.1 In this work, we demonstrate how narrow-band photon bunched light can be generated efficiently from laser light with −7dB conversion efficiency compared to −100dB with established methods. We then showcase a use for such sources by performing clock synchronization of two separate quartz oscillators, achieving synchronization with frequency offset error of 3:2ppb.

DOI
10.1117/12.3063420

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Photon bunching is the phenomenon in which photons in a light field have a higher than random probability of being grouped together.1 In this work, we demonstrate how narrow-band photon bunched light can be generated efficiently from laser light with −7dB conversion efficiency compared to −100dB with established methods. We then showcase a use for such sources by performing clock synchronization of two separate quartz oscillators, achieving synchronization with frequency offset error of 3:2ppb.
Thermal light sources exhibiting photon bunching have been suggested for sensing applications that exploit timing correlations of stationary light, including range finding, clock synchronization, and non-line-of-sight imaging. However, these proposals have remained unrealized in practice because available sources of photon bunching either possess coherence times too short to be timing resolved by photodetectors, or produce brightness levels too low to tolerate realistic return losses. In this work, we demonstrate a low-loss method for generating photon bunching with a conversion efficiency nearly 9 orders of magnitude higher than that achieved by many other bunching processes.
Clock synchronization is necessary for communication and distributed computing tasks. Previous schemes based on photon timing correlations use pulsed light or photon pairs for their strong timing correlations. In this work, we demonstrate successful synchronization of crystal clocks using weakly time-correlated photons of 180 ns coherence time from a bunched light source. A synchronization timing jitter of 10 ns is achieved over symmetric -102 dB optical channel loss between two parties, over a span of 25 hours. We also present a model that gives better estimates to the coherence peak finding success probabilities under low signal.
Temporal photon bunching is the phenomena in which photons tend to cluster together on a short time scale. This effect can be quantified using the second order coherenceg(2)(τ)g^{(2)}(\tau)g(2)(τ)of the light. Photon bunching has been utilized in LIDAR, ghost imaging and simulating star light. In these applications, bunched light is typically generated inefficiently by sending coherent laser light through a phase randomization media, such as a rotating ground glass [1] or a liquid suspension of microspheres [2].
Classical sensing techniques such as range finding and clock synchronization use timing modulated light sources to provide the timing correlations needed for their implementation. Corresponding quantum schemes utilise spontaneous parametric down converted light sources to provide the timing correlations without the need for timing modulation, although entangled states are too fragile to be fully exploited presently. Here we demonstrate the use of thermal light as an alternative source for timing correlations, via the photon bunching generated from a laser operating below threshold, and showcase its practical viability by successful range finding measurements.
Sources of entangled photon pairs are a crucial ingredient for many applications in quantum information and communication. Of particular interest are narrow-band sources with bandwidths that are compatible with solid state systems such as atomic media for storage and manipulation of the photons. Here, we experimentally realize a source of energy-time entangled photon pairs where the photons pairs are generated by scattering light from a single two-level atom and separated from the coherently scattered light via a narrow-band filter. We verify the performance of our pair-source by measuring the second order correlation function of the atomic fluorescence and we observe that one can continuously tune the photon statistics of the atomic fluorescence from perfect photon anti-bunching to strong photon bunching expected for a photon pair source. Our experiment demonstrates a novel way to realize a photon pair source for photons with spectral bandwidths and resonance frequencies that are inherently compatible with atomic media.
In quantum mechanics, photons are bosons -- there is no restriction on the number of them that occupy the same quantum state, so many of them can bunch together, and this is well known as photon bunching effect. However, photon bunching and multiphoton interference of bunched photons have never been directly observed from a broadband thermal chaotic light source. Nevertheless, it has been known that the interference intensity of a number N of bunched photons oscillates with a wavelength of N times shorter than the wavelength of the constituent single photons, which should be observable in Fourier transform spectroscopy. A quantum Fourier transform spectrometer was made based on a Michelson interferometer and a diffraction spectrometer to observe the photon bunching from multiphoton interference of the bunched photons in thermal light. The results demonstrates 2 to 12 bunched photons were observed simultaneously from thousands of wavelengths in the light of a tungsten halogen lamp. The experiment discloses some interesting properties of the bunched photons. The results will provide new insights for advancing the theories of quantum optics, and the new technology opens the way for new precise measurement of photon bunching and multiphoton interference of bunched photons that are in all kinds of light sources or that are generated with quantum entangled photons.