arXiv subjects

Ya-Fen Hsiao

Publications and source records attributed to Ya-Fen Hsiao.

5 recordsLinked to original sources

arXiv2022

Quantum-Logic Gate between Two Optical Photons with an Average Efficiency above 40%

Optical qubits uniquely combine information transfer in optical fibers with a good processing capability and are therefore attractive tools for quantum technologies. A large challenge, however, is to overcome the low efficiency of two-qubit logic gates. The experimentally achieved efficiency in an optical controlled NOT (CNOT) gate reached approximately 11% in 2003 and has seen no increase since. Here we report on a new platform that was designed to surpass this long-standing record. The new scheme avoids inherently probabilistic protocols and, instead, combines aspects of two established quantum nonlinear systems: atom-cavity systems and Rydberg electromagnetically induced transparency. We demonstrate a CNOT gate between two optical photons with an average efficiency of 41.7(5)% at a postselected process fidelity of 81(2)%. Moreover, we extend the scheme to a CNOT gate with multiple target qubits and produce entangled states of presently up to five photons. All these achievements are promising and have the potential to advance optical quantum information processing in which almost all advanced protocols would profit from high-efficiency logic gates.

quant-ph↗

arXiv2020

Broadband coherent optical memory based on electromagnetically induced transparency

Quantum memories, devices that can store and retrieve photonic quantum states on demand, are essential components for scalable quantum technologies. It is desirable to push the memory towards the broadband regime in order to increase the data rate. Here, we present a theoretical and experimental study on the broadband optical memory based on electromagnetically-induced-transparency (EIT) protocol. We first provide a theoretical analysis on the issues and requirements to achieve a broadband EIT memory. We then present our experimental efforts on EIT memory in cold atoms towards the broadband or short-pulse regime. A storage efficiency of ~ 80 % with a pulse duration of 30 ns (corresponding to a bandwidth of 14.7 MHz) is realized. Limited by the available intensity of the control beam, we could not conduct an optimal storage for the even shorter pulses but still obtain an efficiency of larger than 50 % with a pulse duration of 14 ns (31.4 MHz). The achieved time-bandwidth-product at the efficiency of 50 % is 1267.

physics.atom-ph↗

arXiv2019

Quantum storage and manipulation of heralded single photons in atomic quantum memories

We demonstrate the storage and manipulation of narrowband heralded single photons from a cavity-enhanced spontaneous parametric downconversion (SPDC) source in the atomic quantum memory based on electromagnetically induced transparency. We show that nonclassical correlations are preserved between the heralding and the retrieved photons after storage process. By varying the intensity of the coupling field during retrieval process, we further demonstrate that the waveform or bandwidth of the single photons can be manipulated and the nonclassical correlation between the photon pairs can be even enhanced. Unlike previous works, our SPDC source is single mode in frequency, which not only reduces the experimental complexity arising from external filtering but also increases the useful photon generation rate. Our results can be scaled up with ease and thus lay the foundation for future realization of large-scale applications in quantum information processing.

quant-ph↗

arXiv2018

Raman Gray Molasses Cooling of Cesium Atoms on the D2 Line

We present a systematic study on the Raman gray molasses cooling (RGMC) of cesium atoms on the $D_2$ transition. Due to the large splitting in the excited hyperfine transitions of cesium $D_2$ line, it is relatively simple to implement the RGMC with suitable frequency control on the trapping and repumping lasers of the magneto-optical trap (MOT). We have achieved an atom temperature of 1.7$\pm$0.2 $μ$K after the RGMC with $3.2\times 10^8$ atoms. The phase space density is $1.43\times 10^{-4}$. Compared to the condition with a bare MOT or the MOT with a standard polarization gradient cooling, the phase space density increases by a factor of more than $10^3$ or $10$, respectively.

physics.atom-ph↗

arXiv2018

Highly efficient coherent optical memory based on electromagnetically induced transparency

Quantum memory is an important component in the long-distance quantum communication system based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 92.0(1.5)\% for a coherent optical memory based on the electromagnetically induced transparency (EIT) scheme in optically dense cold atomic media. We also obtain a useful time-bandwidth product of 1200, considering only storage where the retrieval efficiency remains above 50\%. Both are the best record to date in all kinds of the schemes for the realization of optical memory. Our work significantly advances the pursuit of a high-performance optical memory and should have important applications in quantum information science.

quant-ph↗