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Quantum Optics and Quantum Information|44 Article(s)
Enhancing optical clock stability via decoupling laser frequency noise and systematic effects
Qichao Qi, Tao Zhang, Taoyun Jin, Shuai Lei, Yan Xia, Jiaxuan Zhang, Hao Chang, Suzhen Feng, Xuan Liu, Jiayi Wang, Rui Zhang, Zhiming Tang, and Xinye Xu
Optical lattice clocks demonstrate advantages in metrology and frontier physics because of their high stability. Here, we present approaches to enhancing the stability by decoupling the noise related to the short-term and long-term stability. For the short-term stability, we optimize the clock laser by decoupling the frequency noise, and optimize each noise contribution individually until it is below the thermal noise limit. For the long-term stability, we introduce a method to decouple the instability caused by systematic effects. Having identified that the collision frequency shift was the main limiting factor in our systems, we thus optimized the atom number fluctuations in optical lattices. Through targeted optimization, we achieve a synchronous comparison of two clocks with an average stability of 3.2×10-16/τ and a long-term stability of 2.4 × 10-18 at 8000 s. This work provides an analytical framework for enhancing optical clock stability. Optical lattice clocks demonstrate advantages in metrology and frontier physics because of their high stability. Here, we present approaches to enhancing the stability by decoupling the noise related to the short-term and long-term stability. For the short-term stability, we optimize the clock laser by decoupling the frequency noise, and optimize each noise contribution individually until it is below the thermal noise limit. For the long-term stability, we introduce a method to decouple the instability caused by systematic effects. Having identified that the collision frequency shift was the main limiting factor in our systems, we thus optimized the atom number fluctuations in optical lattices. Through targeted optimization, we achieve a synchronous comparison of two clocks with an average stability of 3.2×10-16/τ and a long-term stability of 2.4 × 10-18 at 8000 s. This work provides an analytical framework for enhancing optical clock stability.
Chinese Optics Letters
- Publication Date: Jul. 31, 2025
- Vol. 23, Issue 9, 092703 (2025)
Noise-resistant underwater correlated biphoton imaging based on a super-bunching light source
Jinze Li, Yuanyuan Li, Miaoqing Bai, Xiangdong Li, Xuedong Zhang, Ganying Zeng, Zhichun Yang, Xinghui Liu, Jianyong Hu, Ruiyun Chen, Guofeng Zhang, Chengbing Qin, Liantuan Xiao, and Suotang Jia
Single-photon detection (SPD) technologies have been applied to underwater optical imaging to overcome the strong attenuation of seawater. However, external photon noise, resulting from the natural light, hinders their further applications due to the extreme sensitivity of SPD and a weakly received optical signal. In this work, we performed noise-resistant underwater correlated biphoton imaging (CPI) to partly solve the influence of the external noise, through a home-built super-bunching laser generated by the stochastic nonlinear interaction between a picosecond laser and a photonic crystal fiber. Compared with a coherent laser, the probabilities of generated bundle N-photons (N ≥ 2) of the super-bunching laser have been enhanced by at least one order of magnitude, enabling CPI under weak light intensity. We experimentally demonstrated CPI with reasonable imaging contrast under the noise-to-signal ratio (NSR) up to 103, and the noise-resistant performance has been improved by at least two orders of magnitude compared to that of the single-photon imaging technology. We further achieved underwater CPI with good imaging contrast under NSR of 150, in a glass tank with a length of 10 m with Jerlov type III water (an attenuation coefficient of 0.176 m-1). These results break the limits of underwater imaging through classical coherent lasers and may offer many enhanced imaging applications through our super-bunching laser, such as long-range target tracking and deep-sea optical exploration under noisy environments. Single-photon detection (SPD) technologies have been applied to underwater optical imaging to overcome the strong attenuation of seawater. However, external photon noise, resulting from the natural light, hinders their further applications due to the extreme sensitivity of SPD and a weakly received optical signal. In this work, we performed noise-resistant underwater correlated biphoton imaging (CPI) to partly solve the influence of the external noise, through a home-built super-bunching laser generated by the stochastic nonlinear interaction between a picosecond laser and a photonic crystal fiber. Compared with a coherent laser, the probabilities of generated bundle N-photons (N ≥ 2) of the super-bunching laser have been enhanced by at least one order of magnitude, enabling CPI under weak light intensity. We experimentally demonstrated CPI with reasonable imaging contrast under the noise-to-signal ratio (NSR) up to 103, and the noise-resistant performance has been improved by at least two orders of magnitude compared to that of the single-photon imaging technology. We further achieved underwater CPI with good imaging contrast under NSR of 150, in a glass tank with a length of 10 m with Jerlov type III water (an attenuation coefficient of 0.176 m-1). These results break the limits of underwater imaging through classical coherent lasers and may offer many enhanced imaging applications through our super-bunching laser, such as long-range target tracking and deep-sea optical exploration under noisy environments.
Chinese Optics Letters
- Publication Date: Sep. 08, 2025
- Vol. 23, Issue 9, 092702 (2025)
Polarization in quantum photonic sensing [Invited]|Editors' Pick
Luosha Zhang, Chengjun Zou, Yu Wang, Frank Setzpfandt, and Vira R. Besaga
In this review, we address the emerging field of quantum photonic sensing leveraging the polarization degree of freedom. We briefly discuss the main aspects of treating polarization in quantum optics, and provide an overview of the main trends in the development of the field and the strategies to realize quantum-enhanced polarization-based sensing as well as a comprehensive survey of the main advancements in the field. We aim at promoting quantum approaches to the researchers in classical optical polarimetry as well as underscoring the sustainability and resourcefulness of the field for prospective applications and attracting the researchers in quantum optics to this new emerging field. In this review, we address the emerging field of quantum photonic sensing leveraging the polarization degree of freedom. We briefly discuss the main aspects of treating polarization in quantum optics, and provide an overview of the main trends in the development of the field and the strategies to realize quantum-enhanced polarization-based sensing as well as a comprehensive survey of the main advancements in the field. We aim at promoting quantum approaches to the researchers in classical optical polarimetry as well as underscoring the sustainability and resourcefulness of the field for prospective applications and attracting the researchers in quantum optics to this new emerging field.
Chinese Optics Letters
- Publication Date: Aug. 13, 2025
- Vol. 23, Issue 9, 092701 (2025)
Large Purcell enhancement with a narrow linewidth in all-dielectric nanoantenna-microtoroid structures
Zihan Mo, Yali Jia, Xinchen Zhang, Yu Tian, and Ying Gu
Large Purcell enhancement, requiring high-quality factors and small mode volumes, is essential to single-photon sources. Whispering gallery microcavities possessing a high-quality factor are limited by a large mode volume, while dielectric nanoantennas with an ultra-small mode volume suffer from significant scattering loss. Here, by combining the advantages of the microtoroids and the nanoantennas, we achieve large Purcell enhancement with a narrow linewidth in all-dielectric nanoantenna-microtoroid hybrid structures. The scattering loss of the nanoantenna is suppressed by the high-Q microtoroids; meanwhile, its ultra-small mode volume remains almost unchanged. As a result, the Purcell factor of the emitter located at the gap of the nanoantenna reaches as high as 1000–1700, while its linewidth is kept at the order of hundreds of picometers. The proposed mechanism holds promise for applications in on-chip single-photon sources and low-threshold nanolasers. Large Purcell enhancement, requiring high-quality factors and small mode volumes, is essential to single-photon sources. Whispering gallery microcavities possessing a high-quality factor are limited by a large mode volume, while dielectric nanoantennas with an ultra-small mode volume suffer from significant scattering loss. Here, by combining the advantages of the microtoroids and the nanoantennas, we achieve large Purcell enhancement with a narrow linewidth in all-dielectric nanoantenna-microtoroid hybrid structures. The scattering loss of the nanoantenna is suppressed by the high-Q microtoroids; meanwhile, its ultra-small mode volume remains almost unchanged. As a result, the Purcell factor of the emitter located at the gap of the nanoantenna reaches as high as 1000–1700, while its linewidth is kept at the order of hundreds of picometers. The proposed mechanism holds promise for applications in on-chip single-photon sources and low-threshold nanolasers.
Chinese Optics Letters
- Publication Date: Jul. 22, 2025
- Vol. 23, Issue 8, 082703 (2025)
High similarity quantum correlation imaging using a flat-top beam
Kai Wang, Rongshi Chen, Fei Han, Nanxiang Zhao, Xinyuan Zhang, Qingli Ma, Shilong Xu, and Yihua Hu
Quantum correlation imaging plays an important role in quantum information processing. The existing quantum correlation imaging schemes mostly use the Gaussian beam as the pump source, resulting in the entangled two photons exhibiting a Gaussian distribution. In this Letter, we report the experimental demonstration of quantum correlation imaging using a flat-top beam as the pump source, which can effectively solve the problem of imaging distortion. The sampling time for each point is 5 s, and the imaging similarity is 93.4%. The principle of this scheme is reliable, the device is simple, and it can achieve high-similarity quantum correlation imaging at room temperature. Quantum correlation imaging plays an important role in quantum information processing. The existing quantum correlation imaging schemes mostly use the Gaussian beam as the pump source, resulting in the entangled two photons exhibiting a Gaussian distribution. In this Letter, we report the experimental demonstration of quantum correlation imaging using a flat-top beam as the pump source, which can effectively solve the problem of imaging distortion. The sampling time for each point is 5 s, and the imaging similarity is 93.4%. The principle of this scheme is reliable, the device is simple, and it can achieve high-similarity quantum correlation imaging at room temperature.
Chinese Optics Letters
- Publication Date: Jul. 14, 2025
- Vol. 23, Issue 8, 082702 (2025)
Broadband energy-time entangled photon-pair source based on a fiber-pigtailed PPLN waveguide [Invited]|Editors' Pick
Peng Wu, Yunru Fan, Hao Yu, Guangwei Deng, You Wang, Haizhi Song, Hao Li, Lixing You, Guangcan Guo, and Qiang Zhou
We report a broadband energy-time entangled photon-pair source based on a fiber-pigtailed periodically poled lithium niobate (PPLN) waveguide, designed for applications in the quantum secure network. Utilizing the spontaneous parametric down-conversion nonlinear optical process, the source generates entangled photon pairs within a wavelength range of 64 nm in the telecom band at a pump wavelength of 770.3 nm. Photon pairs from eight paired International Telecommunication Union (ITU) channels are selected, and their correlation and entanglement properties are characterized. The measured coincidence counts of photon pairs from eight paired ITU channels are larger than 152.9 kHz when the coincidence-to-accidental ratios are greater than 260. Entanglement properties are measured through two-photon interference in the Franson interferometer, with all visibilities of interference curves exceeding 98.13%. Our demonstration provides a broadband energy-time entangled photon-pair source, contributing to the development of a large-scale quantum secure network. We report a broadband energy-time entangled photon-pair source based on a fiber-pigtailed periodically poled lithium niobate (PPLN) waveguide, designed for applications in the quantum secure network. Utilizing the spontaneous parametric down-conversion nonlinear optical process, the source generates entangled photon pairs within a wavelength range of 64 nm in the telecom band at a pump wavelength of 770.3 nm. Photon pairs from eight paired International Telecommunication Union (ITU) channels are selected, and their correlation and entanglement properties are characterized. The measured coincidence counts of photon pairs from eight paired ITU channels are larger than 152.9 kHz when the coincidence-to-accidental ratios are greater than 260. Entanglement properties are measured through two-photon interference in the Franson interferometer, with all visibilities of interference curves exceeding 98.13%. Our demonstration provides a broadband energy-time entangled photon-pair source, contributing to the development of a large-scale quantum secure network.
Chinese Optics Letters
- Publication Date: Jul. 14, 2025
- Vol. 23, Issue 8, 082701 (2025)
Entanglement-assisted polarimeter for phase retardance measurement
Mengyu Xie, Sujian Niu, Zheng Ge, Mingyuan Gao, Zhaoqizhi Han, Renhui Chen, Yinhai Li, Zhiyuan Zhou, and Baosen Shi
Polarimeter is a vital precision tool used for measuring optical parameters through polarization variations. Among the wide range of application fields, the precise measurement of photosensitive materials is an unavoidable task but faces immense obstacles due to the excessive input photons. Facing this situation, introducing a quantum source into the classical precision measurement system is a feasible way to enhance the detection accuracy under the low illumination regime. In this work, we employ polarization-entangled photon pairs in the classical polarimeter to precisely detect the relative phase retardance of uniform anisotropic media. The experimental results show that the accuracy can reach the nanometer scale at extremely low input intensity, and the stabilities are within 0.4% for all samples. Our work paves the way for polarization measurement at low incident light intensity, with potential applications in measuring photosensitive materials and remote monitoring scenarios. Polarimeter is a vital precision tool used for measuring optical parameters through polarization variations. Among the wide range of application fields, the precise measurement of photosensitive materials is an unavoidable task but faces immense obstacles due to the excessive input photons. Facing this situation, introducing a quantum source into the classical precision measurement system is a feasible way to enhance the detection accuracy under the low illumination regime. In this work, we employ polarization-entangled photon pairs in the classical polarimeter to precisely detect the relative phase retardance of uniform anisotropic media. The experimental results show that the accuracy can reach the nanometer scale at extremely low input intensity, and the stabilities are within 0.4% for all samples. Our work paves the way for polarization measurement at low incident light intensity, with potential applications in measuring photosensitive materials and remote monitoring scenarios.
Chinese Optics Letters
- Publication Date: Jun. 16, 2025
- Vol. 23, Issue 7, 072701 (2025)
Non-unitary transformation on quantum interference in a chip
Jiani Lei, Yilin Yang, Hao Li, Zixuan Liao, Bo Tang, Yuanhua Li, Yuanlin Zheng, and Xianfeng Chen
In quantum information processing, unitary transformations are oftentimes used to implement computing tasks. However, unitary transformations are not enough for all situations. Therefore, it is important to explore non-unitary transformations in quantum computing and simulation. Here, we introduce non-unitary transformations by performing singular value decomposition (SVD) on two-photon interference. Through simulation, we show that losses modeled by non-unitary transformation can be perceived as variables to control two-photon interference continuously, and the coincidence statistics can be changed by an appropriate choice of observation basis. The results are promising in the design of integrated optical circuits, providing a way toward fabricating large-scale programmable circuits. In quantum information processing, unitary transformations are oftentimes used to implement computing tasks. However, unitary transformations are not enough for all situations. Therefore, it is important to explore non-unitary transformations in quantum computing and simulation. Here, we introduce non-unitary transformations by performing singular value decomposition (SVD) on two-photon interference. Through simulation, we show that losses modeled by non-unitary transformation can be perceived as variables to control two-photon interference continuously, and the coincidence statistics can be changed by an appropriate choice of observation basis. The results are promising in the design of integrated optical circuits, providing a way toward fabricating large-scale programmable circuits.
Chinese Optics Letters
- Publication Date: Apr. 29, 2025
- Vol. 23, Issue 5, 052701 (2025)
Ten-channel Hong–Ou–Mandel interference between independent optical combs|Fast Track
Wenhan Yan, Yang Hu, Yifeng Du, Kai Wang, Yan-Qing Lu, Shining Zhu, and Xiao-Song Ma
The dissipative Kerr soliton (DKS) frequency comb exhibits broad and narrow-linewidth frequency modes, which make it suitable for quantum communication. However, a scalable quantum network based on multiple independent combs is still a challenge due to fabrication-induced frequency mismatches. This limitation becomes critical in measurement-device-independent quantum key distribution, which requires high visibility of Hong–Ou–Mandel interference between multiple frequency channels. Here, we experimentally demonstrate two independent DKS combs with 10 spectrally aligned lines without any frequency locking system. The visibility for individual comb-line pairs reaches up to 46.72% ± 0.63% via precision frequency translation, establishing a foundation for deploying DKS combs in multi-user quantum networks. The dissipative Kerr soliton (DKS) frequency comb exhibits broad and narrow-linewidth frequency modes, which make it suitable for quantum communication. However, a scalable quantum network based on multiple independent combs is still a challenge due to fabrication-induced frequency mismatches. This limitation becomes critical in measurement-device-independent quantum key distribution, which requires high visibility of Hong–Ou–Mandel interference between multiple frequency channels. Here, we experimentally demonstrate two independent DKS combs with 10 spectrally aligned lines without any frequency locking system. The visibility for individual comb-line pairs reaches up to 46.72% ± 0.63% via precision frequency translation, establishing a foundation for deploying DKS combs in multi-user quantum networks.
Chinese Optics Letters
- Publication Date: Apr. 24, 2025
- Vol. 23, Issue 4, 042701 (2025)
Integration of classical communication and quantum key distribution using frequency division multiplexing
Yunyu Shao, Ziyi Shen, Yuehan Xu, Lang Li, Zicong Tan, Xiaojuan Liao, Peng Huang, Tao Wang, and Guihua Zeng
Since the working conditions of classical and quantum signals are very different, how to effectively integrate classical and quantum communication networks without affecting their respective performance has become a great challenge. In this paper, we proposed a scheme to realize classical communication and continuous-variable quantum key distribution (CV-QKD) based on frequency-division multiplexing (FDM), and we verified the feasibility of simultaneously realizing CV-QKD and classical optical communication data synchronous transmission scheme under the same infrastructure. We achieved a 0 bit error rate in 50 frames and a 20 Mb/s bit rate for the classical signal and an average secret key rate of around 5.86 × 105 bit/s for the quantum signal through a 4 dB fiber channel. This work provides a scheme to establish a QKD channel by only reserving a small passband in the entire optical communication instead of an entire wavelength, increasing efficiency and simplifying the integration of QKD and classical communication. Since the working conditions of classical and quantum signals are very different, how to effectively integrate classical and quantum communication networks without affecting their respective performance has become a great challenge. In this paper, we proposed a scheme to realize classical communication and continuous-variable quantum key distribution (CV-QKD) based on frequency-division multiplexing (FDM), and we verified the feasibility of simultaneously realizing CV-QKD and classical optical communication data synchronous transmission scheme under the same infrastructure. We achieved a 0 bit error rate in 50 frames and a 20 Mb/s bit rate for the classical signal and an average secret key rate of around 5.86 × 105 bit/s for the quantum signal through a 4 dB fiber channel. This work provides a scheme to establish a QKD channel by only reserving a small passband in the entire optical communication instead of an entire wavelength, increasing efficiency and simplifying the integration of QKD and classical communication.
Chinese Optics Letters
- Publication Date: Mar. 25, 2025
- Vol. 23, Issue 3, 032702 (2025)
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