Recent Posters
Here shows the selected posters for recent years.
2026
Conversion Of Biphoton OAM Entanglement Into Polarization Toward Fiber-compatible Quantum Networking
ABSTRACT
We demonstrate polarization-entangled biphotons in acold-atom double-Λ system, overcoming atomic selection rules that suppress polarization correlations and favor orbital angular momentum (OAM) entanglement. Using spatial light modulators (SLMs), we coherently map a selected two-dimensional OAM subspace onto the polarization basis and thereby open an otherwise inaccessible polarization channel. Quantum-state tomography confirms that the mapping preserves the biphoton coherence. The four polarization Bell states are generated with fidelities of 92–94%with few-percent statistical uncertainties, and an average Clauser–Horne–Shimony–Holt parameter of S = 2.44 verifies the survival of nonlocal correlations. To the best of our knowledge, this work provides the first demonstration of OAM-to-polarization entanglement transfer in a cold-atom SFWM platform and establishes a practical interface for integrating atomic OAM resources with polarization-based quantum communication networks.
2026
Superradiant telecom-to-near-infraredbiphoton generation in a diamond-type atomicensemble with broadly tunable bandwidth
ABSTRACT
Telecom and optical two-color biphotons enable the connection of different frequency bands without quantum interfaces, which is essential for quantum networksand long-distance quantum communication. In this study, we demonstrate the generation of telecom-to-near-infrared biphotons in a diamond-type atomicensemble. Using the Heisenberg-Langevin operator method, we show that the biphoton wave packet exhibits superradiant behavior governed by the collectivespontaneous emission time. By increasing the optical depth of the medium, we control the biphoton correlation time from the single-atom spontaneous emissiontime to the sub-nanosecond scale, resulting in a broadly tunable bandwidth from MHz to GHz. Our theoretical predictions align well with experimentalobservations, confirming that the biphoton correlation time follows the superradiant scaling behavior observed in a simple two-level system. Additionally, byincorporating the Doppler effect, we extend our model to room-temperature atoms, where the temporal width of Doppler-broadened biphotons is further reduceddue to interference among atomic velocity classes. This study provides deep insights into the superradiant effects of two-color biphotons with a broadly tunablebandwidth and may advance their applications in photonic quantum communications and information processing.
2026
Quantum-Correlated Visible-to-Telecom Biphotons viaDiamond-type Atomic-Ensemble Frequency Conversion
ABSTRACT
Quantum frequency conversion to the telecom band is a key enabling technology for scalable fiber-based quantum networks. Atom-basedplatforms offer intrinsic advantages including narrow bandwidths and high signal to noise ratios, making them well suited for high fidelity quantum state transfer.Here we demonstrate efficient visible to telecom conversion of quantum correlated biphotons generated in cold 87Rb atomic ensembles. Native biphoton pairs at 780nm and 795 nm exhibit a pronounced peak cross correlation of approximately 18 prior to conversion. The 795 nm photon is subsequently frequency converted to 1367 nm through a diamond-type four-wave mixing process implemented in a second cold atom ensemble, achieving a conversion efficiency of up to 80%. Afterconversion, the peak cross correlation remains as high as about 10, which is well above the classical limit and confirms the preservation of nonclassical correlations.By directly verifying the retention of biphoton correlations through atom-based frequency conversion, this work goes beyond previous demonstrations based onDLCZ-type single photon sources and establishes a robust pathway for distributing quantum correlations in the telecom band for practical quantum networking.
2025
Frequency-tunable biphoton generation via spontaneousfour-wave mixing
ABSTRACT
We present experimental results on tuning biphoton frequency by introducing a detuned coupling field in spontaneous four-wave mixing (SFWM), and examine its impact on the pairingratio. This tunability is achieved by manipulating the inherent electromagnetically induced transparency (EIT) effect in the double-Λ scheme. Introducing a detuned coupling fielddegrades the efficiency of EIT-based stimulated four-wave mixing, which in turn reduces the biphoton pairing ratio. However, this reduction can be mitigated by increasing the opticalpower of the coupling field. Additionally, we observe that blue- and red-detuning the biphoton frequency results in distinct temporal profiles of biphoton wavepackets due to phasemismatch. These findings provide insights into the mechanisms of frequency-tunable biphoton generation via SFWM, and suggest potential optimizations for applications in quantumcommunication and information processing.
2024
Highly Correlated Ultrabright Biphotons via Spontaneous Four-Wave Mixing
ABSTRACT
The pairing ratio, a metric quantifying a biphoton source‘s ability to generate correlated photon pairs, is crucial for assessing source quality. Despite theoretical predictions, the intrinsic characteristic of the pairing ratio has remained largely unexplored in experiments. In this study, we present experimental findings on the pairing ratio using a double-Λ spontaneous four-wave mixing biphoton source in cold atoms. At an optical depth (OD) of 20, we achieved an ultrahigh biphoton generation rate, reaching up to 1.3 × 10⁷ per second, with a successful pairing ratio of 61%. Increasing the OD to 120 significantly improved the pairing ratio to 89%, while maintaining a consistent biphoton generation rate. This dual achievement, characterized by high generation rates and robust biphoton pairing, holds great promise for enhancing efficiency in quantum communication and information processing. Furthermore, in a scenario with a lower biphoton generation rate of 5.0×10⁴ per second, we attained an impressive signal-to-background ratio of 241 for the biphoton wavepacket, surpassing the Cauchy-Schwarz criterion by approximately 1.5×10⁴ times.
2024
Quantum Interface for Telecom Frequency Conversion Based on
Diamond Type Atomic Ensembles
ABSTRACT
In a fiber-based quantum network, quantum frequency conversion (QFC) serves as a pivotal quantum interface for efficiently bridging the frequency gap between atomic quantum devices and telecom fibers. In this study, we explore an efficient telecom-band QFC mechanism based on diamond-type four-wave mixing (FWM) with rubidium energy levels. The mechanism enables the conversion of photons between the near-infrared wavelength of 795 nm and the telecom band of 1367 or 1529 nm. Using the Heisenberg-Langevin approach, we optimize conversion efficiency (CE) across varying optical depths while addressing the applied field absorption loss and present corresponding experimental parameters. Moreover, by employing the reduced-density-operator theory to construct a theoretical framework, we demonstrate that this diamond-type FWM scheme can maintain the quantum characteristics of input photons with high fidelity, such as quadrature variances and photon statistics. Importantly, these properties remain unaffected by vacuum field noise, enabling the system to achieve high-purity QFC. Another significant contribution lies in examining how this scheme impacts quantum information (QI) encoded in photon-number, path, and polarization degrees of freedom (DOFs). These encoded qubits exhibit remarkable entanglement retention under sufficiently high CE and achieve unity fidelity for perfect CE. This comprehensive exploration establishes a theoretical foundation for the application of the diamond-type QFC scheme based on atomic ensembles in quantum networks, laying essential groundwork for advancing the scheme in distributed quantum computing and long-distance quantum communication.
2023
Color Photonic Quantum Logic Gates
ABSTRACT
Hong−Ou−Mandel (HOM) interference is a compelling quantum phenomenon that demonstrates the nonclassical nature of single photons. In this study, we investigate an electromagnetically induced transparency-based double-Λ four-wave mixing system from the perspective of quantized light fields. The system can be used to realize efficient HOM interference in the frequency domain. By using the reduced density operator theory, we demonstrate that, although the double-Λ medium does not exhibit phase-dependent properties for the closed-loop case of two incident single photons, frequency-domain HOM two-photon interference occurs. For experimentally achievable optical depth conditions, our theory indicates that this double-Λ scheme can perform high-fidelity Hadamard gate operations on frequency-encoded single-photon qubits, and thereby generate HOM two-photon NOON states with a fidelity greater than 0.99. Furthermore, we demonstrate that this scheme can be used to realize arbitrary single-qubit gates and two-qubit SWAP gates by simply controlling the laser detuning and phase, exhibiting its multifunctional properties and providing a new route to scalable optical quantum information processing.
2023
High Purity Biphoton Source from Slow Light to Rabi Oscillation Regimes
ABSTRACT
In optical quantum computing and quantum communication, single photons or flying qubits play a crucial role as quantum information carriers due to their remarkable nonclassical properties. To implement deterministic photonic logic gates, it is often necessary to precisely control the interaction time of single photons in optical quantum circuits, so heralded single-photon sources become essential Biphoton pairs generated by spontaneous four-wave mixing (SFWM) in atomic media, which can be used to implement heralded single photon sources, have attracted extensive attention due to their built-in quantum memory and bandwidth controllable features. Here, we experimentally realize an efficient biphoton source based on double-Λ SFWM in cold atoms. By controlling the applied laser intensity and detuning, a series of biphoton wavepackets from slow light to Rabi oscillation regimes are observed We demonstrate the highest signal-to-background ratio of the biphoton wavepacket up to 61 which violates the Cauchy Schwarz criterion by a factor of more than 900, revealing its single-photon properties with high purity Furthermore, by increasing the driving Rabi frequency and reducing the driving detuning, we achieved an ultra-high biphoton generation rate of 1 3 × 10^7 /s, which, to our knowledge, is the highest generation rate of the heralded single-photon source based on the double-Λ scheme to date.
