Recent Posters
Here shows the selected posters for recent years.
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.
2021
Quantum Frequency Conversion Based on Resonant Four-Wave Mixing
ABSTRACT
Quantum frequency conversion (QFC), a critical technology in photonic quantum information science, requires that the quantum characteristics of the frequency-converted photon must be the same as the input photon except for the color. In nonlinear optics, the wave mixing effect far away from the resonance condition is often used to realize QFC because it can prevent the vacuum field reservoir from destroying the quantum state of the converted photon effectively. However, the strong pump light used in nonlinear optics often generates additional noise photons through spontaneous Raman or parametric conversion processes. Herein, we theoretically study another efficient QFC scheme based on a resonant four-wave mixing system. Due to the effect of electromagnetically induced transparency (EIT), this resonant QFC scheme can greatly suppress vacuum field noise at low light levels; consequently, the converted photons can inherit the quantum state of the input photon with high fidelity. Our research demonstrates that if the conversion efficiency (CE) of the EIT-based QFC is close to 100%, the wave function and quadrature variance of the converted photons are almost the same as the input probe photons. Using this resonant QFC scheme, we observe a wavelength conversion from 780 to 795 nm with a 91.2(6)% CE in a cold 87Rb atomic cloud with an optical depth of 130. The current work shows that our proposed and demonstrated resonant four-wave mixing system is a feasible and promising scheme to realize low-loss, high-fidelity QFC.
2018
High-efficiency backward four-wave mixing by quantum interference
ABSTRACT
Long-distance quantum optical communications usually require efficient wave-mixing processes to convert the wavelengths of single photons. Many quantum applications based on electromagnetically induced transparency (EIT) have been proposed and demonstrated at the photon level, such as quantum memories, all-optical transistors, and cross-phase modulations. However, EIT-based four-wave mixing (FWM) in a resonant double-Λ configuration has a maximum conversion efficiency (CE) of 25% because of absorptive loss due to spontaneous emission. Here, we demonstrate that spontaneous emission can be considerably suppressed by arranging the applied laser beams in a backward configuration. With the backward double-Λ FWM scheme, we observe a CE of 76% in cold rubidium atoms with an optical depth (OD) of 52. Furthermore, we present a theoretical model that includes the phase-mismatch effect in the backward double-Λ FWM system. According to the theoretical model, the present scheme can achieve 96% CE using a medium with a large OD of 200 under ideal conditions. This backward FWM scheme can achieve a near-unity CE, thus providing an easy method of implementing an efficient quantum wavelength converter for narrow-band single photons in all-optical quantum information processing.
2017
Large Cross-Phase Modulations at the Few-Photon Level
ABSTRACT
We demonstrate an efficient cross-phase modulation (XPM) based on a closed-loop double-Λ system. The property of the double-Λ medium can be controlled by changing the phases of the applied optical fields. This phase-dependent XPM scheme can achieve large phase modulations at low-light intensities without requiring cavities or tightly focusing laser beams. With this scheme, we observe a π-level phase shift with two pulses, both consisting of eight photons in cold rubidium atoms. Such a novel scheme provides a simple route to generate strong interactions between photons and may have potential applications in all-optical quantum signal processing.