arXiv subjects

Ren-Hui Chen

Publications and source records attributed to Ren-Hui Chen.

8 recordsLinked to original sources

arXiv2025

Long-distance distribution of atom-photon entanglement based on a cavity-free cold atomic ensemble

Constructing a quantum memory node with the ability of long-distance atom-photon distribution is the essential task for future quantum networks, enabling distributed quantum computing, quantum cryptography and remote sensing. Here we report the demonstration of a quantum-network node with a simple cavity-free cold atomic ensemble. This node gives an initial retrieval efficiency of approximately 50\% and memory lifetime of 160 $\mu$s for atomic qubits. With the aid of a high-efficiency and polarization-independent quantum frequency conversion (QFC) module, the generated entangled photon in the node at 780-nm wavelength is converted to telecom S band at 1522 nm, enabling atom-photon distribution over long distance. We observe an entanglement fidelity between the atoms and telecom photon exceeding 80\% after photon transmission over 20-km fiber, the remaining infidelity being dominated by atomic decoherence. The low-noise QFC with an external efficiency up to 48.5\% gives a signal-to-noise-ratio of 6.9 for transmitted photons with fiber length up to 100 km, laying the cornerstone for entanglement distribution at a hundred-km level. This result provides a new platform towards the realization of a long-distance quantum network.

quant-ph↗

arXiv2025

Widely tunable cavity-enhanced backward difference-frequency generation

Difference-frequency generation (DFG) is a powerful technique for generating widely tunable infrared radiation. However, conventional phase-matching schemes may require tuning multiple parameters-such as the wavelengths, crystal temperature, crystal angle, and poling period-to achieve wide tunability, which increases the complexity of practical operation. In this work, we employ a backward quasi-phase-matching scheme with distinctive tuning characteristics and demonstrate pump-enhanced continuous-wave DFG output tunable from 1751 nm to 2451 nm (700 nm range) in a bulk crystal. The tuning is achieved solely by varying the pump wavelength and the signal wavelength (less than 5 nm), enabling continuous, rapid, and room-temperature operation. The tuning characteristics, power-scaling behavior, and output stability are experimentally verified with the idler wavelength set at 2000 nm. The approach offers a new paradigm for widely tunable infrared radiation generation and holds promise for applications in spectroscopy and biomedical sensing.

physics.optics↗

arXiv2025

On Chip Quantum States Generation by Incoherent Light

On-chip quantum sources based on nonlinear processes are pivotal components in integrated photonics, driving significant advancements in quantum information technologies over recent decades. Usually, the pump coherence has been considered to be crucial for ensuring the quality of generated states, therefore incoherent light is rarely used in quantum information processing. In this work, we explore and reveal the constructive influence of pumped temporal incoherence on the quantum properties of photon sources. Taking silicon waveguides as nonlinear media, we theoretically show that temporal incoherence of light can improve pumping utilization efficiency, resulting in higher source brightness in a spontaneous four-wave mixing process, and the spectrally uncorrelated nature of incoherent light is transferred to the generated photon source, allowing high-purity state preparation. Experimentally, we obtain a higher photon pair generation rate and the lower heralded second-order autocorrelation with an Amplified Spontaneous Emission source. Additionally, we successfully generate a polarization-entangled state with Bell inequality violation of S = 2.64 and a fidelity of 95.7%. Our study reveals the mechanism behind incoherently pumped quantum states and presents a method for generating photon sources using an easily accessible incoherent light.

quant-ph↗

arXiv2025

An all optical broadband tunable quantum frequency shifter

A frequency shifter of the photon is a key component for frequency-multiplexed high-capacity quantum communications and frequency-encoded quantum computation. Existed methods for shifting the frequency of a photon based on electro-optical, or acousto-optical effect, however, suffer the limited frequency shift up to a few hundreds of GHz, furthermore, high-quality micro-wave electronics are required. The frequency of a photon can also be shifted with the frequency difference equal to the frequency of pump laser by using an all optical-wave-mixing approach, which is usually about tens of THz. So, there is a big frequency shifting gap between these methods. Here, we propose a new scheme of a quantum frequency shifter based on an all-optical wave-mixing process, which can theoretically achieve a frequency shift ranging from GHz to a few THz, therefore bridging the gap. As a principle of poof, by using two pump beams in a three-wave mixing cascading process, a heralded single photon is frequency-shifted more than 400GHz, and the shift can be tuned continuously over broadband by changing the frequency difference between two pump lasers. Besides, high coincidence to accidence ratio between the shifted photons and the heralded photon indicates the preserve of quantum properties. The present quantum frequency shifter is in analog to an electro-optical based shifter, but with much broader tuning ability. Our all-optical quantum frequency shifter will become a fundamental building block for high-speed quantum communication networks and frequency domain photonic quantum computation.

quant-ph↗

arXiv2024

Quantum key distribution based on mid-infrared and telecom band two-color entanglement source

Due to the high noise caused by solar background radiation, the existing satellite-based free-space quantum key distribution (QKD) experiments are mainly carried out at night, hindering the establishment of a practical all-day real-time global-scale quantum network. Given that the 3-5 μm mid-infrared (MIR) band has extremely low solar background radiation and strong scattering resistance, it is one of the ideal bands for free-space quantum communication. Here, firstly, we report on the preparation of a high-quality MIR (3370 nm) and telecom band (1555 nm) two-color polarization-entangled photon source, then we use this source to realize a principle QKD based on free-space and fiber hybrid channels in a laboratory. The theoretical analysis clearly shows that a long-distance QKD over 500 km of free-space and 96 km of fiber hybrid channels can be reached simultaneously. This work represents a significant step toward developing all-day global-scale quantum communication networks.

quant-ph↗

arXiv2024

Quantum-Enhanced Polarimetric Imaging

Polarimetric imaging, a technique that captures the invisible polarization-related properties of given materials, has broad applications from fundamental physics to advanced fields such as target recognition, stress detection, biomedical diagnosis and remote sensing. The introduction of quantum sources into classical imaging systems has demonstrated distinct advantages, yet few studies have explored their combination with polarimetric imaging. In this study, we present a quantum polarimetric imaging system that integrates polarization-entangled photon pairs into a polarizer-sample-compensator-analyzer (PSRA)-type polarimeter. Our system visualizes the birefringence properties of a periodical-distributed anisotropic material under decreasing illumination levels and diverse disturbing light sources. Compared to the classical system, the quantum approach reveals the superior sensitivity and robustness in low-light conditions, particularly useful in biomedical studies where the low illumination and non-destructive detection are urgently needed. The study also highlights the nonlocality of entangled photons in birefringence measurement, indicating the potential of quantum polarimetric system in the remote sensing domain.

physics.optics↗

arXiv2024

Effective multiband synthetic four-wave mixing by cascading quadratic processes

Four wave mixing (FWM) is an important way to generate supercontinuum and frequency combs in the mid-infrared band. Here, we obtain simultaneous synthetic FWM in the visible and mid-infrared bands by cascading quadratic nonlinear processes in a periodically poled lithium niobate crystal (PPLN), which has a 110dB(at 3000nm) higher conversion efficiency than the FWM directly generated by third-order susceptibilities in bulk PPLN crystals. A general model of this process is developed that is in full agreement with the experimental verifications. The frequency difference between the new frequency components can be freely tuned by changing the frequency difference of the dual pump lasers. Furthermore, by increasing the conversion bandwidth and efficiency of the cascaded processes, it is feasible to generate frequency combs in three bands the visible, near-infrared and mid-infrared bands simultaneously through high-order cascaded processes. This work opens up a new avenue toward free-tuning multiband frequency comb generation with multi-octaves frequency spanning, which will have significant applications in fields such as mid-infrared gas sensing, lidar and precision spectroscopy.

physics.optics↗

arXiv2024

Quantum entanglement enabled ellipsometer for phase retardance measurement

An ellipsometer is a vital precision tool used for measuring optical parameters with wide applications in many fields, including accurate measurements in film thickness, optical constants, structural profiles, etc. However, the precise measurement of photosensitive materials meets huge obstacles because of the excessive input photons, therefore the requirement of enhancing detection accuracy under low incident light intensity is an essential topic in the precision measurement. In this work, by combining a polarization-entangled photon source with a classical transmission-type ellipsometer, the quantum ellipsometer with the PSA (Polarizer-Sample-Analyzer) and the Senarmount method is constructed firstly to measure the phase retardation of the birefringent materials. The experimental results show that the accuracy can reach to nanometer scale at extremely low input intensity, and the stability are within 1% for all specimens tested with a compensator involved. Our work paves the way for precision measurement at low incident light intensity, with potential applications in measuring photosensitive materials, active-biological samples and other remote monitoring scenarios.

quant-ph↗