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arXiv:2103.03419

Direct observation of photon bunching in thermal light in quantum Fourier transform spectroscopy

Dianwen Zhang

Published Mar 5, 2021• 0 citations
arXivHTMLPDF

Abstract

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.

DOI
10.48550/arxiv.2103.03419

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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.
Bosonic bunching is a term used to describe the well-known tendency of bosons to bunch together, and which differentiates their behavior from that of fermions or classical particles. However, in some situations, perfectly indistinguishable bosons may counter-intuitively bunch less than classical, distinguishable particles. Here, we report two such counter-intuitive multiphoton bunching effects observed with three photons in a three-mode balanced photonic Fourier interferometer. In this setting, we show that indistinguishable photons actually minimize the probability of bunching. We also show that any non-trivial value of the three-photon collective photonic phase leads to a decreased probability of all photons ending up in the same mode, even as we increase pairwise indistinguishability. Our experiments feature engineering of partial indistinguishability scenarios using both the time and the polarization photonic degrees of freedom, and a polarization-transparent 8-mode tunable interferometer with a quantum-dot source of single photons. Besides the foundational understanding, the observation of these counter-intuitive phenomena open news perspective in devising more efficient ways of routing photons for advantage in metrology and quantum computation.
Photons emitted by incoherent sources exhibit temporal bunching, a fundamental manifestation of Bose-Einstein statistics first observed by Hanbury Brown and Twiss (HBT). While intensity correlation measurements originated in astronomy and are now central across quantum technologies, biophysics, and spectroscopy, observing temporal bunching in broadband thermal light remains limited by detector temporal resolution. Conventional approaches - such as streak cameras or optical upconversion - introduce severe trade-offs in efficiency, bandwidth, or setup versatility. Here, we propose and demonstrate a third route: pre-detection temporal magnification of the optical field prior to measuring its intensity autocorrelation function in a conventional HBT setup. Using an electro-optic time lens with a temporal magnification of 660, we resolve the temporal intensity autocorrelation of broadband thermal light generated via non-degenerate spontaneous parametric down-conversion with a bandwidth of 250 GHz. This enables direct observation of thermal photon bunching on sub-3.5 picosecond timescales without narrow spectral filtering, establishing pre-detection temporal imaging as a general platform for broadband statistical optics, with applications spanning ultrafast quantum optics, biophysical imaging, and potentially stellar intensity interferometry.
Thermal light by nature exhibits the well-known photon bunching effect with the zero-delay second-order correlation coefficient g(2){g}^{(2)}g(2) ideally equal to 2. The Photon extra-bunching effect, as a special class of the superbunching effect (g(2)>2{g}^{(2)}>2g(2)>2), describes the enhanced photon correlation (g(2)=3{g}^{(2)}=3g(2)=3) through the interference of bright twin beams produced in the spontaneous parametric down-conversion. In this work, we report that this effect can exist in classical beams and that g(2){g}^{(2)}g(2) can approach 4 in some extended extreme models. We experimentally demonstrate the nontrivial extra-bunching correlation ($\ensuremath{\sim}1.4\ifmmode\times\else\texttimes\fi{}$ gain) in pairwise-generated holographic thermal light beams with a Dove prism-embedded balanced Mach-Zehnder interferometer. The interaction of such a pair of conjugated thermal light beams can generate a pair of uncorrelated superthermal light beams, enabling ghost imaging and Young's intensity interference with enhanced visibility. The quantum-inspired interference-induced spatial extra-bunching effect provides novel insights into inducing superbunching correlation in classical light and holds the potential for application in the coherent two-photon Lidar system to enhance sensitivity.
Two-photon interference is a fundamental resource for quantum technologies and optical quantum computing, underpinning precision measurements, scalable entanglement distribution, and the operation of photonic circuits and quantum network protocols. Here, we report the first demonstration of massively parallel, wavelength-resolved photon bunching, revealing Hanbury Brown–Twiss correlations across 70 independent spectral channels. These observations are enabled by a fast, data-driven single-photon spectrometer that achieves 48 pm spectral and 48 ps temporal resolution over a 10 nm bandwidth, providing simultaneous access to spectro-temporal photon correlations without the need for narrowband filtering. This approach enables high-dimensional quantum interference measurements across a broad spectrum. Our results establish frequency-multiplexed two-photon interference as a scalable and throughput-efficient platform for quantum-enhanced photonic technologies, offering a practical route toward room-temperature architectures that overcome loss limitations and advance the scalability for a variety of applications.
Understanding the boundary between classical and nonclassical phenomena is important for both fundamental researches in quantum optics and applications in quantum information. One of the most interesting research directions in this field is exploring nonclassical effects with classical light. In this paper, we will show that it is possible to observe antibunching with thermal light in a Hanbury Brown-Twiss interferometer by treating single-photon detectors as photon-number-resolving detectors to perform photon-number projection measurements. Both temporal and spatial antibunching is observed via the correlation of two detectors detecting one and zero photon, respectively. By comparing the measured results of thermal and laser light, it is found that the observed antibunching arises from the combined effect of photon statistics of thermal light and photon-number projection measurement.The classical and nonclassical nature of the observed antibunching is analyzed. The results are helpful to understand the connection between classical and nonclassical correlation and may find applications in multiphoton interference and quantum imaging.