Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review Letters

Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles

Peng Qian, Zhenjie Gu, Rong Cao, Rong Wen, Z. Y. Ou, J. F. Chen, Weiping Zhang

Published Jul 1, 2016• 41 citations
Publisher

Abstract

The temporal purity of single photons is crucial to the indistinguishability of independent photon sources for the fundamental study of the quantum nature of light and the development of photonic technologies. Currently, the technique for single photons heralded from time-frequency entangled biphotons created in nonlinear crystals does not guarantee the temporal-quantum purity, except using spectral filtering. Nevertheless, an entirely different situation is anticipated for narrow-band biphotons with a coherence time far longer than the time resolution of a single-photon detector. Here we demonstrate temporally pure single photons with a coherence time of 100 ns, directly heralded from the time-frequency entangled biphotons generated by spontaneous four-wave mixing in cold atomic ensembles, without any supplemented filters or cavities. A near-perfect purity and indistinguishability are both verified through Hong-Ou-Mandel quantum interference using single photons from two independent cold atomic ensembles. The time-frequency entanglement provides a route to manipulate the pure temporal state of the single-photon source.

DOI
10.1103/physrevlett.117.013602

Related papers

Temporal pure single photons generated from time-frequency entangled biphotons

Peng Qian, Zhejie Gu, J. F. Chen +1 more

Narrow-band time-frequency entangled biphotons are generated from spontaneous four-wave mixing in cold atom clouds. The coherence time of the entangled biphotons can be extended to sub-microseconds by the slow light effect. The temporal wavefunction of the biphotons can be manipulated through modulating the spectral or spatial mode of the controlling laser beams. Concerning a pair of entangled biphoton and the resulting heralded single photon, it was commonly believed that, time-frequency entanglement damages the temporal purity of the single photon. However, the case is totally different for biphotons with long coherence time which is far beyond the time resolution of single-photondetectors. We demonstrate that, the single photon heralded from these time-frequency entangled biphotons is in a pure temporal state. Therefore, single photons are able to be shaped through the time-frequency entanglement with their partner photons, while the single photons could be found to be still in a pure state and thus useful for quantum information processing and communication technology.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Nov 3, 2016•0 citations

Temporal interference with frequency-controllable long photons from independent cold atomic sources

Peng Qian, Zhenjie Gu, Rong Wen +2 more

The interference of single photons from independent sources is an essential tool in quantum information processing. However, the interfering of photons with long temporal states in a time-resolved manner has rarely been studied. This is because without transmitting spectral filters or coupling to a cavity mode single photons generated in traditional nonlinear crystals suffer from a short temporal profile below 1 ns. With spectral correlation maintained in the biphotons generated from spontaneous four-wave mixing process in cold atom clouds, here we demonstrate the temporal interference of two frequency-tunable long photons from two independent cold atomic sources. We observe and analyze the interference of frequency-mismatched photons, where the phenomenon of the quantum beat at megahertz separation is displayed. Our paper provides more details for the quantum beat of two independent narrow-band single photons, which may find potential application in frequency-encoded photonic qubits in quantum information processing.

Physical Review A•Jan 4, 2018•5 citations

TEMPORAL PURITY, QUANTUM INTERFERENCE, AND RELATIONAL OBJECTIVITY

Vidamor Cabannas

The experiment reported by Peng Qian and collaborators in “Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles,” published in Physical Review Letters in 2016, provides an unusu- ally productive empirical platform for a critical–propositional dialogue with the Theory of Objectivity (TO). Qian et al. generated narrow-band time–frequency- entangled biphotons through spontaneous four-wave mixing in two independent cold 85Rbatomicensemblesanddemonstratedtheproductionof temporallypureheraldedsinglephotons.T emporalpurityandindistinguishabilitywereinvestigatedthroughHong− −Ou−−M andelinterferencebetweenphotonsoriginatingfromphysicallyseparateatomicsources. The experiment reported coherence times of approximately 100,ns, temporal- profile similarity of approximately 97approximately 80experimental limitations were present (Qian et al. 2016). The authors further showed that the product of photon bandwidth and temporal uncertainty, [ BW∆T, ] constitutes a physically meaningful parameter governing temporal purity, with the heralded single-photon state approaching the pure regime when [ BW∆T ≤ 0.1.] This article examines those findings under the modal discipline of the Theory of Objectivity, particularly its First, Second, and Fifth Absolute Truths. The analysis rigorously distinguishes modal necessity, empirical compatibility, indirect corroboration, and experimental confirmation. The Qian experiment does not address primordial logical Nothingness and therefore does not empirically support the First Absolute Truth concerning a logical, mathematical, and eternal pre-cosmic essence. By contrast, the experiment creates a sig- nificant conceptual and potentially operational dialogue with the Second Absolute Truth, according to which each existing element possesses its own exclusive individualizing field, and with the Fifth Absolute Truth, according to which logical existence requires relational observation or frequency inclusion involving at least two other elements. The ability of independently generated photons to become operationally indis- tinguishable constitutes both a challenge and an opportunity for the TO: it constrains any experimentally meaningful interpretation of the proposed individualizing field while suggesting a route toward a discriminating Hong–Ou–Mandel test. Particular attention is given to the TO concept of the transcendent element as information or knowledge produced through atomic relations and considered equivalent to atomic radiation. Qian et al. provide a concrete physical system in which atomic interactions generate radiation bearing controllable time–frequency information. The experiment therefore offers a significant operational analogy, although not an ontological demonstration, of the TO information–radiation thesis. The analysis further considers phenomenic elements, Inductor Effects, boundary structures, the cosmogonic theorem, and the cosmological eras of the TO. It concludes that Qian et al. constitute a strong case of relational and informational dialogue with the Theory of Objectivity while simultaneously illustrating the necessity of converting modal propositions into quantitative predictions capable of discriminating TO-specific consequences from those already predicted by standard quantum mechanics. Keywords: Theory of Objectivity; temporal purity; Hong–Ou–Mandel interference; quantum optics; single photons; cold atomic ensembles; information; atomic radiation; modal ontology; relational observation; indistinguishability; spontaneous four-wave mixing.

•Oct 4, 2026•0 citations

Controlling the interference of single photons emitted by independent atomic sources

Alessandro Ceré, Victor Leong, Sandoko Kosen +3 more

Hong-Ou-Mandel interference between independent sources is a fundamental primitive of many quantum communication and computation protocols. We present a study of the Hong-Ou-Mandel interference of single photons generated via two different physical processes by two independent atomic systems: scattering by a single atom, and parametric generation via four-wave mixing in a cloud of cold atoms. By controlling the coherence time and central frequency of the heralded single photons generated by four-wave mixing we observe quantum beat and a varying degree of interference.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Sep 1, 2015•0 citations

Quantum-state purity of heralded single photons produced from frequency-anticorrelated biphotons

Shengwang Du

We analyze the quantum-state purity of heralded single photons produced from frequency-anticorrelated biphotons. We find that the quantum-state purity in the time-frequency domain depends strongly on the response time uncertainty of the trigger-photon detector that heralds the generation of its paired photon. If the trigger response time is much shorter than the two-photon coherence time, the time-frequency quantum-state purity of heralded single photons approaches unity and the heralded single photon is in a nearly pure state. If the trigger response time is much longer than the two-photon coherence time, the heralded photon is then projected onto a mixed state. Making use of the time-frequency entanglement, heralded single photons with a well-defined temporal wave function or a frequency superposition state can be produced and engineered. This time-frequency entanglement allows for shaping heralded single photons through nonlocal spectral modulation.

arXiv:1507.03483•Physical Review A•Oct 28, 2015•29 citations

Generation of biphotons with long correlation time in cold atoms

Luwei Zhao

Driven by the desire of narrow-band photon pairs source, in this Mphil thesis work, we demonstrate the generation of photon pairs with controllable coherence time up to 1.72 microseconds, using spontaneous four-wave mixing with electromagnetically induced transparency in a laser-cooled atomic ensemble with an optical depth (OD) as high as 130. At such a high OD, we find that the pump laser intensity profile has a significant effect on the time-frequency entangled two-photon waveform. We also confirm the quantum particle nature of heralded narrow-band single photons generated from this source.

•Jan 1, 2014•0 citations
The temporal purity of single photons is crucial to the indistinguishability of independent photon sources for the fundamental study of the quantum nature of light and the development of photonic technologies. Currently, the technique for single photons heralded from time-frequency entangled biphotons created in nonlinear crystals does not guarantee the temporal-quantum purity, except using spectral filtering. Nevertheless, an entirely different situation is anticipated for narrow-band biphotons with a coherence time far longer than the time resolution of a single-photon detector. Here we demonstrate temporally pure single photons with a coherence time of 100 ns, directly heralded from the time-frequency entangled biphotons generated by spontaneous four-wave mixing in cold atomic ensembles, without any supplemented filters or cavities. A near-perfect purity and indistinguishability are both verified through Hong-Ou-Mandel quantum interference using single photons from two independent cold atomic ensembles. The time-frequency entanglement provides a route to manipulate the pure temporal state of the single-photon source.
Narrow-band time-frequency entangled biphotons are generated from spontaneous four-wave mixing in cold atom clouds. The coherence time of the entangled biphotons can be extended to sub-microseconds by the slow light effect. The temporal wavefunction of the biphotons can be manipulated through modulating the spectral or spatial mode of the controlling laser beams. Concerning a pair of entangled biphoton and the resulting heralded single photon, it was commonly believed that, time-frequency entanglement damages the temporal purity of the single photon. However, the case is totally different for biphotons with long coherence time which is far beyond the time resolution of single-photondetectors. We demonstrate that, the single photon heralded from these time-frequency entangled biphotons is in a pure temporal state. Therefore, single photons are able to be shaped through the time-frequency entanglement with their partner photons, while the single photons could be found to be still in a pure state and thus useful for quantum information processing and communication technology.
The interference of single photons from independent sources is an essential tool in quantum information processing. However, the interfering of photons with long temporal states in a time-resolved manner has rarely been studied. This is because without transmitting spectral filters or coupling to a cavity mode single photons generated in traditional nonlinear crystals suffer from a short temporal profile below 1 ns. With spectral correlation maintained in the biphotons generated from spontaneous four-wave mixing process in cold atom clouds, here we demonstrate the temporal interference of two frequency-tunable long photons from two independent cold atomic sources. We observe and analyze the interference of frequency-mismatched photons, where the phenomenon of the quantum beat at megahertz separation is displayed. Our paper provides more details for the quantum beat of two independent narrow-band single photons, which may find potential application in frequency-encoded photonic qubits in quantum information processing.
The experiment reported by Peng Qian and collaborators in “Temporal Purity and Quantum Interference of Single Photons from Two Independent Cold Atomic Ensembles,” published in Physical Review Letters in 2016, provides an unusu- ally productive empirical platform for a critical–propositional dialogue with the Theory of Objectivity (TO). Qian et al. generated narrow-band time–frequency- entangled biphotons through spontaneous four-wave mixing in two independent cold 85Rbatomicensemblesanddemonstratedtheproductionof temporallypureheraldedsinglephotons.T emporalpurityandindistinguishabilitywereinvestigatedthroughHong− −Ou−−M andelinterferencebetweenphotonsoriginatingfromphysicallyseparateatomicsources. The experiment reported coherence times of approximately 100,ns, temporal- profile similarity of approximately 97approximately 80experimental limitations were present (Qian et al. 2016). The authors further showed that the product of photon bandwidth and temporal uncertainty, [ BW∆T, ] constitutes a physically meaningful parameter governing temporal purity, with the heralded single-photon state approaching the pure regime when [ BW∆T ≤ 0.1.] This article examines those findings under the modal discipline of the Theory of Objectivity, particularly its First, Second, and Fifth Absolute Truths. The analysis rigorously distinguishes modal necessity, empirical compatibility, indirect corroboration, and experimental confirmation. The Qian experiment does not address primordial logical Nothingness and therefore does not empirically support the First Absolute Truth concerning a logical, mathematical, and eternal pre-cosmic essence. By contrast, the experiment creates a sig- nificant conceptual and potentially operational dialogue with the Second Absolute Truth, according to which each existing element possesses its own exclusive individualizing field, and with the Fifth Absolute Truth, according to which logical existence requires relational observation or frequency inclusion involving at least two other elements. The ability of independently generated photons to become operationally indis- tinguishable constitutes both a challenge and an opportunity for the TO: it constrains any experimentally meaningful interpretation of the proposed individualizing field while suggesting a route toward a discriminating Hong–Ou–Mandel test. Particular attention is given to the TO concept of the transcendent element as information or knowledge produced through atomic relations and considered equivalent to atomic radiation. Qian et al. provide a concrete physical system in which atomic interactions generate radiation bearing controllable time–frequency information. The experiment therefore offers a significant operational analogy, although not an ontological demonstration, of the TO information–radiation thesis. The analysis further considers phenomenic elements, Inductor Effects, boundary structures, the cosmogonic theorem, and the cosmological eras of the TO. It concludes that Qian et al. constitute a strong case of relational and informational dialogue with the Theory of Objectivity while simultaneously illustrating the necessity of converting modal propositions into quantitative predictions capable of discriminating TO-specific consequences from those already predicted by standard quantum mechanics. Keywords: Theory of Objectivity; temporal purity; Hong–Ou–Mandel interference; quantum optics; single photons; cold atomic ensembles; information; atomic radiation; modal ontology; relational observation; indistinguishability; spontaneous four-wave mixing.
Hong-Ou-Mandel interference between independent sources is a fundamental primitive of many quantum communication and computation protocols. We present a study of the Hong-Ou-Mandel interference of single photons generated via two different physical processes by two independent atomic systems: scattering by a single atom, and parametric generation via four-wave mixing in a cloud of cold atoms. By controlling the coherence time and central frequency of the heralded single photons generated by four-wave mixing we observe quantum beat and a varying degree of interference.
We analyze the quantum-state purity of heralded single photons produced from frequency-anticorrelated biphotons. We find that the quantum-state purity in the time-frequency domain depends strongly on the response time uncertainty of the trigger-photon detector that heralds the generation of its paired photon. If the trigger response time is much shorter than the two-photon coherence time, the time-frequency quantum-state purity of heralded single photons approaches unity and the heralded single photon is in a nearly pure state. If the trigger response time is much longer than the two-photon coherence time, the heralded photon is then projected onto a mixed state. Making use of the time-frequency entanglement, heralded single photons with a well-defined temporal wave function or a frequency superposition state can be produced and engineered. This time-frequency entanglement allows for shaping heralded single photons through nonlocal spectral modulation.
Driven by the desire of narrow-band photon pairs source, in this Mphil thesis work, we demonstrate the generation of photon pairs with controllable coherence time up to 1.72 microseconds, using spontaneous four-wave mixing with electromagnetically induced transparency in a laser-cooled atomic ensemble with an optical depth (OD) as high as 130. At such a high OD, we find that the pump laser intensity profile has a significant effect on the time-frequency entangled two-photon waveform. We also confirm the quantum particle nature of heralded narrow-band single photons generated from this source.