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Advanced Photonics Research

Highly Efficient Biphoton Generation from Thin Dense Atomic Ensemble

Heewoo Kim, Hansol Jeong, Han Seb Moon

Published Apr 1, 2025• 0 citations
Publisher

Abstract

Highly Efficient Biphoton Generation In article number 2400214, Han Seb Moon, Heewoo Kim, and Hansol Jeong present a highly efficient biphoton source using a thin and dense atomic medium from a hot 1 mm-long Cs atomic vapor cell, which paves the way for scalable quantum networks. Demonstrating the viability of such atomic sources at the millimeter scale marks a significant milestone, driving the miniaturization of quantum technologies and advancing light-matter interfaces.

DOI
10.1002/adpr.202570009

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Highly Efficient Biphoton Generation from Thin Dense Atomic Ensemble

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arXiv:2109.09062•Physical Review Research•May 18, 2022•30 citations
Highly Efficient Biphoton Generation In article number 2400214, Han Seb Moon, Heewoo Kim, and Hansol Jeong present a highly efficient biphoton source using a thin and dense atomic medium from a hot 1 mm-long Cs atomic vapor cell, which paves the way for scalable quantum networks. Demonstrating the viability of such atomic sources at the millimeter scale marks a significant milestone, driving the miniaturization of quantum technologies and advancing light-matter interfaces.
Hybrid photonic quantum networks require photonic quantum states generated from different systems, such as atoms and quantum dots. Photonic quantum sources based on atomic ensembles are excellent candidates due to their brightness, low noise, and narrowband characteristics. Herein, a new platform for a highly efficient biphoton source is presented using a thin, dense atomic medium from a hot 1 mm‐long chip‐scale Cs atomic vapor cell. Strongly correlated bright biphotons are generated via spontaneous four‐wave mixing from a dense atomic ensemble based on the 6S1/2–6P3/2–6D5/2 transition of 133Cs. Biphoton source achieves a detected biphoton count rate of 100 kilo‐counts per second, a heralding efficiency of 15%, and a maximum normalized crosscorrelation function value of 100 between the signal and idler photons, despite the low detector efficiency of a silicon avalanche photodetector being less than 25% at 917 nm. Herein, the maximal violation of the Cauchy–Schwarz inequality by a factor greater than 106 at a pump power of 1 μW is obtained. The scheme for a highly efficient photon source is believed to be useful for scalable quantum networks.
The realization of a narrowband photonic quantum source based on an atomic device is considered essential in the practical development of photonic quantum information science and technology. In this study, we present the first step toward the development of a photon-pair source based on a microfabricated Cs atomic vapor cell. Time-correlated photon pairs from the millimeter-scale Cs vapor cell are emitted via the spontaneous four-wave mixing process of the cascade-type 6S1/2–6P3/2–8S1/2 transition of 133Cs. The maximum normalized cross-correlation value between the signal and idler photons is measured as 622(8) under a weak pump power of 10 µ;W. Our photon source violates the Cauchy–Schwartz inequality by a factor of >105. We believe that our approach has very important applications in the context of realizing practical scalable quantum networks based on atom–photon interactions.
Abstract The realization of a narrowband photonic quantum source based on a chip-scale atomic device is considered essential in the practical development of photonic quantum information science and technology. In this study, we present the first step toward the development of a photon-pair source based on a microfabricated chip-scale Cs atomic vapor cell. Time-correlated photon pairs from the millimeter-scale Cs vapor cell are emitted via the spontaneous four-wave mixing process of the cascade-type 6S1/2–6P3/2–8S1/2 transition of 133Cs. The maximum normalized cross-correlation value between the signal and idler photons is measured as 622(8) under a weak pump power of 10 mW. Our photon source violates the Cauchy–Schwartz inequality by a factor of >105. We believe that our approach has very important applications in the context of realizing practical scalable quantum networks based on atom–photon interactions.
Superradiance is one of the most fundamental collective quantum phenomena in light-matter interactions and has been studied extensively since Dicke's seminal work. However, its practical implementation remains challenging because superradiant enhancement requires strict experiment conditions for strong collective coupling among emitters. Can superradiance emerge in a simple platform, such as an atomic vapor cell composed of thermally moving atoms? To address this question, we identify the key signatures of superradiance in a hot atomic ensemble and find a use case of superradiance using an atomic vapor cell. Here, the Photon-Pair SuperRadiance (PPSR) process in an atomic vapor cell provides a novel approach to generating superradiant quantum light from a practical atomic platform. We experimentally demonstrate a superradiant entangled photon-pair generation via PPSR process in a high-density, 1-mm-long chip-scale Cs vapor cell. The hot, dense atomic vapor cell allows the mean interatomic distance in the Doppler-broadened atomic ensemble to be reduced to 0.29 times the idler-photon wavelength, satisfying the condition for cooperative emission. The thin chip-scale geometry enables high atomic densities while mitigating the reabsorption of emitted photons and maintaining moderate optical depth. In this subwavelength regime, we clearly observe the temporal narrowing of the biphoton wavefunction from 0.60 ns to 0.17 ns due to a superradiant decay. This pronounced temporal compression provides strong evidence of collective superradiant emission in the chip-scale Cs vapor cell. Our PPSR source delivers a detected photon-pair rate exceeding 10^6 pairs/s while maintaining a high coincidence-to-accidental ratio of 280.
Biphotons, generated from a hot atomic vapor via the process of spontaneous four-wave mixing (SFWM), have the following merits: Stable and tunable frequencies as well as linewidth. Such merits are very useful in the application of long-distance quantum communication. However, the hot-atom SFWM biphoton sources previously had far lower values of generation rate per linewidth, i.e., spectral brightness, as compared with the sources of biphotons generated by the spontaneous parametric down-conversion process. Here we report a hot-atom SFWM source of biphotons with a linewidth of 960 kHz and a generation rate of $3.7\ifmmode\times\else\texttimes\fi{}{10}^{5}$ pairs/s. The high generation rate, together with the narrow linewidth, results in a spectral brightness of $3.8\ifmmode\times\else\texttimes\fi{}{10}^{5}$ pairs/s/MHz, which is 17 times the previous best result with atomic vapors and also better than all known results with all kinds of media. The all-co-propagating scheme together with a large optical depth (OD) of the atomic vapor is the key improvement, enabling the achieved spectral brightness to be about one quarter of the ultimate limit. Furthermore, this biphoton source had a signal-to-background ratio (SBR) of 2.7, which violated the Cauchy-Schwartz inequality for classical light by about 3.6-fold. Although an increasing spectral brightness usually leads to a decreasing SBR, our systematic study indicates that both of the present spectral brightness and SBR can be enhanced by further increasing the OD. This work demonstrates a significant advancement and provides useful knowledge in quantum technology using photons.