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Chen, YH, Lee MJ, Wang IC, Du SW, Chen YF, Chen YC, Yu IA.  2013.  Coherent Optical Memory with High Storage Efficiency and Large Fractional Delay, Feb. Physical Review Letters. 110:5., Number 8 AbstractWebsite

A high-storage efficiency and long-lived quantum memory for photons is an essential component in long-distance quantum communication and optical quantum computation. Here, we report a 78% storage efficiency of light pulses in a cold atomic medium based on the effect of electromagnetically induced transparency. At 50% storage efficiency, we obtain a fractional delay of 74, which is the best up-to-date record. The classical fidelity of the recalled pulse is better than 90% and nearly independent of the storage time, as confirmed by the direct measurement of phase evolution of the output light pulse with a beat-note interferometer. Such excellent phase coherence between the stored and recalled light pulses suggests that the current result may be readily applied to single photon wave packets. Our work significantly advances the technology of electromagnetically induced transparency-based optical memory and may find practical applications in long-distance quantum communication and optical quantum computation. DOI: 10.1103/PhysRevLett.110.083601

Hsiao, Y-F, Tsai P-J, Lin C-C, Chen Y-F, Yu IA, Chen Y-C.  2014.  Coherence properties of amplified slow light by four-wave mixing. Optics Letters. 39(12):3394-3397. Abstract

We present an experimental study of the coherence properties of amplified slow light by four-wave mixing (FWM) in a three-level electromagnetically induced transparency (EIT) system driven by one additional pump field. High energy gain (up to 19) is obtained with a weak pump field (a few mW∕cm2) using optically dense cold atomic gases. A large fraction of the amplified light is found to be phase incoherent to the input signal field. The dependence of the incoherent fraction on pump field intensity and detuning and the control field intensity is systematically studied. With the classical input pulses, our results support a recent theoretical study by Lauk et al. [Phys. Rev. A 88, 013823 (2013)], showing that the noise resulting from the atomic dipole fluctuations associated with spontaneous decay is significant in the high gain regime. This effect has to be taken into consideration in EIT-based applications in the presence of FWM.

Hsiao, Y-F, Chen H-S, Tsai P-J, Chen Y-C.  2014.  Cold atomic media with ultrahigh optical depths. Phys. Rev. A. 90:054401. Abstract

We present an experimental study to achieve ultrahigh optical depths for cold atomic media with a two dimensional magneto-optical trap (MOT) of cesium. By combining large atom number, a temporally dark and compressed MOT, and Zeeman-state optical pumping, we achieve an optical depth of up to 1306 for the open transition of the cesium D1 line. Our work demonstrates that it is feasible to push the optical depth up to the 1000 level with a convenient MOT setup. This development paves the way to many important proposals in quantum optics and many-body physics.

Chen, Y-H, Lee M-J, Hung W, Chen Y-C, Chen Y-F, Yu IA.  2014.  Interaction between two stopped light pulses. AIP Conference Proceedings . 1588:17-26. Abstract

The efficiency of a nonlinear optical process is proportional to the interaction time. We report a scheme of all-optical switching based on two motionless light pulses via the effect of electromagnetically induced transparency. One pulse was stopped as the stationary light pulse (SLP) and the other was stopped as stored light. The time of their interaction via the medium can be prolonged and, hence, the optical nonlinearity is greatly enhanced. Using a large optical density (OD) of 190, we achieved a very long interaction time of 6.9 μs. This can be analogous to the scheme of trapping light pulses by an optical cavity with a Q factor of 8×109. With the approach of using moving light pulses in the best situation, a switch can only be activated at 2 photons per atomic absorption cross section. With the approach of employing a SLP and a stored light pulse, a switch at only 0.56 photons was achieved and the efficiency is significantly improved. Moreover, the simulation results are in good agreement with the experimental data and show that the efficiency can be further improved by increasing the OD of the medium. Our work advances the technology in quantum information manipulation utilizing photons.

Chiu, C-K, Chen Y-H, Chen Y-C, Yu IA, Chen Y-C, Chen Y-F.  2014.  Low-light-level four-wave mixing by quantum interference. Phys. Rev. A. 89:5. Abstract

We observed electromagnetically induced transparency-based four-wave mixing (FWM) in the pulsed regime at low light levels. The FWM conversion efficiency of 3.8(9)% was observed in a four-level system of cold 87Rb atoms using a driving laser pulse with a peak intensity of ≈80 μW/cm2, corresponding to an energy of ≈60 photons per atomic cross section. Comparison between the experimental data and the theoretical predictions proposed by Harris and Hau [Phys. Rev. Lett. 82, 4611 (1999)] showed good agreement. Additionally, a high conversion efficiency of 46(2)% was demonstrated when applying this scheme using a driving laser intensity of ≈1.8 mW/cm2. According to our theoretical predictions, this FWM scheme can achieve a conversion efficiency of nearly 100% when using a dense medium with an optical depth of 500.

Jen, HH, Chang MS, Chen YC.  2016.  Cooperative single-photon subradiant states. Physical Review A. 94(1):013803.
Lee, C-Y, Wu B-H, Wang G, Chen Y-F, Chen Y-C, Yu IA.  2016.  High conversion efficiency in resonant four-wave mixing processes. Optics Express. 24 :1008-1016.
Chen, Y-H, Chen Y-C, Yu IA.  2016.  High-Efficiency Coherent Light Storage for the Application of Quantum Memory. AAPPS Bulletin. 26(5)
Liu, Z-Y, Chen Y-H, Chen Y-C, Lo H-Y, Tsai P-J, Yu IA, Chen Y-C, Chen Y-F.  2016.  Large Cross-Phase Modulations at the Few-Photon Level. Phys. Rev. Lett. 117(203601)
Jen, HH, Chen YC.  2016.  Spectral shaping of cascade emissions from multiplexed cold atomic ensembles. Physical Review A. 93 :013811.
Chen, T-J, Chen J-E, Yu H-H, Liu T-W, Hsiao Y-F, Chen Y-C, Chang M-S, Cheng W-Y.  2018.  Absolute frequency of cesium 6S1/2–6D3/2 hyperfine transition with a precision to nuclear magnetic octupole interaction. Optics Letters. 43(9)
Jen, HH, Chang M-S, Chen Y-C.  2018.  Cooperative light scattering from helical-phase-imprinted atomic rings. Scientific Reports. 8(9570)
Hsiao, Y-F, Tsai P-J, Chen H-S, Lin S-X, Hung C-C, Lee C-H, Chen Y-H, Chen Y-F, Yu IA, Chen Y-C.  2018.  Highly Efficient Coherent Optical Memory Based on Electromagnetically Induced Transparency. Phys. Rev. Lett. 120(183602)
Tsai, P-J, Chen Y-C.  2018.  Ultrabright, narrow-band photon-pair source for atomic quantum memories. Quantum Sci. Technol. 3 (034005)
Hsiao, Y-F, Lin Y-J, Chen Y-C.  2018.  Λ -enhanced gray-molasses cooling of cesium atoms on the D 2 line. Phys. Rev. A. 98(033419)
Chang, K-F, Wang T-P, Chen C-Y, Chen Y-H, Wang Y-S, Chen Y-F, Chen Y-C, Yu IA.  2019.  Low-Loss High-Fidelity Frequency-Mode Hadamard Gates Based on Electromagnetically Induced Transparency. arXiv. 1907.03393
Jen, HH, Chang M-S, Lin G-D, Chen Y-C.  2019.  Subradiance dynamics in a singly-excited chiral-coupled atomic chain. arXiv:1905.00558.
Wei, Y-C, Hsiao Y-F, Wu B-H, Tsai P-J, Chen Y-C.  2020.  Broadband coherent optical memory based on electromagnetically induced transparency. Phys. Rev. A. 102, 063720Link
Wei, Y-C, Lin S-X, Tsai P-J, Chen Y-C.  2020.  Memory-based optical polarization conversion in a double-Λ atomic system with degenerate Zeeman states. Sci Rep. 10, 13990 (2020) Link
Tsai, P-J, Hsiao Y-F, Chen Y-C.  2020.  Quantum storage and manipulation of heralded single photons in atomic quantum memories. Phys. Rev. Research. 2(033155)Link
Jen, HH, Chang M-S, Lin G-D, Chen YC.  2020.  Subradiance dynamics in a singly excited chirally coupled atomic chain. PHYSICAL REVIEW A. 101(023830)Link
Tsai, P-J, Wei Y-C, Wu B-H, Li S-X, Chen Y-C.  2020.  Theoretical study on memory-based optical converter with degenerate Zeeman states. Phys. Rev. A. 100(063843)Link
Cheng, C-Y, Liu Z-Y, Hu P-S, Wang T-N, Chien C-Y, Shiu J-S, Yu IA, Chen Y-C, Chen Y-F.  2021.  Efficient frequency conversion based on electromagnetically induced transparency. Optics Letters. 46, 681(2021)
Hsu, C-Y, Wang Y-S, Chen J-M, Huang F-C, Ke Y-T, Huang EK, Hung W, Chao K-L, Hsaio S-S, Chen Y-H, Chuu C-S, Chen Y-C, Chen Y-F, Yu IA.  2021.  Generation of sub-MHz and spectrally-bright biphotons from hot atomic vapors with a phase mis-match-free scheme. Optics Express. 29, 4632(2021)