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Chan, Y-H, Jiang H-C, Chen Y-C.  2023.  Plaquette valence bond state in the spin- 12 J1 -J2 XY model on the square lattice.. PHYSICAL REVIEW B. 107, 214402(2023)
Chang, K-F, Wang T-P, Chen C-Y, Chen Y-H, Wang Y-S, Chen Y-F, Chen Y-C, Yu IA.  2021.  Low-loss, high-fidelity frequency beam splitter with tunable split ratio based on electromagnetical-ly induced transparency. Phys. Rev. Research. 3, 013096 (2021)
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
Chen, YC, Lin WB, Hsue HC, Hsu L, Yu IA.  2000.  Effect of the trapping laser linewidth on the atom number in a magneto-optical trap, Oct. Chinese Journal of Physics. 38:920-926., Number 5 AbstractWebsite

We have experimentally studied the effect of the trapping laser linewidth on the number of capped atoms in a magneto-optical trap (MOT). Our data show that a significant number of the atoms can still be trapped in the MOT, even when the trapping laser linewidth is larger than the natural linewidth of the excited state of the driving transition.

Chen, J-M, Hsu C-Y, Huang W-K, Hsiao S-S, Huang F-C, Chen Y-H, Chuu C-S, Chen Y-C, Chen Y-F, Yu IA.  2022.  Room-temperature biphoton source with a spectral brightness near the ultimate limit. Phys. Rev. Research. 4, 023132(2022)
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

Chen, YW, Lin CW, Chen YC, Yu IA.  2002.  Quantization axes in coherent two-field spectroscopy, Aug. Journal of the Optical Society of America B-Optical Physics. 19:1917-1921., Number 8 AbstractWebsite

Coherent two-field spectroscopy calculations with different choices of the quantization (z) axis are compared. In a system driven by a strong coupling field and a weak probe field, alignment of the z axis along either the polarization direction of a linearly polarized coupling field or the propagation direction of a circularly polarized coupling field is shown to simplify the calculations and facilitate interpretation of the results. The advantages of a suitable choice of the z axis are highlighted with an example of a degenerate three-level system of electromagnetically induced transparency. (C) 2002 Optical Society of America.

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)
Chen, Y-H, Chen Y-C, Yu IA.  2016.  High-Efficiency Coherent Light Storage for the Application of Quantum Memory. AAPPS Bulletin. 26(5)
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.

Chen, Y-H, Lee M-J, Hung W, Chen Y-C, Chen Y-F, Yu IA.  2012.  Demonstration of the Interaction between Two Stopped Light Pulses. Physical Review Letters. 108:173603. AbstractWebsite
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Chen, YC, Liao YA, Hsu L, Yu IA.  2001.  Simple technique for directly and accurately measuring the number of atoms in a magneto-optical trap, Sep. Physical Review A. 64 AbstractWebsite

We have systematically studied a simple technique that accurately determines number of atoms in a magneto-optical trap, Absorption energy of a laser field that interacts with cold atoms is a direct measurement of atom number. The measured energy neither depends on the detuning, intensity, and polarization of the laser field nor is affected by other system parameters. Our work also demonstrates that such technique can be applied to study the phenomenon of coherent population trapping.

Chen, J-M, Hsu C-Y, Huang W-K, Hsiao S-S, Huang F-C, Chen Y-H, Chuu C-S, Chen Y-C, Chen Y-F, Yu IA.  2022.  Room-temperature biphoton source with a spectral brightness near the ultimate limit.. Physical Review Research. 4, 023132(2022)
Chen, YC, Chen YW, Su JJ, Huang JY, Yu IA.  2001.  Pump-probe spectroscopy of cold Rb-87 atoms in various polarization configurations, Apr. Physical Review A. 63:11., Number 4 AbstractWebsite

We investigate systematically pump-probe spectroscopy of cold Rb-87 atoms produced by a magneto-optical trap. The pump-probe spectra are measured without the presence of the trapping beams or any optical molasses. Various polarization configurations of the probe and pump fields result in very different spectra of probe absorption. The observed spectra exhibit a dispersive profile, a dispersionlike profile, a Lorentzian profile, or a dispersive profile plus a Lorentzian profile. The widths of all the spectral profiles are narrower than the natural linewidth of the excited state. Our work clarifies the mechanisms behind these different spectral profiles and provides essential information for the pump-probe spectroscopy of cold atoms.

Chen, YC, Lin CW, Yu IA.  2000.  Role of degenerate Zeeman levels in electromagnetically induced transparency, May. Physical Review A. 61:6., Number 5 AbstractWebsite

We have observed various Lambda-type electromagnetically induced transparency (EIT) spectra in laser-cooled Rb-87 atoms of different laser polarization configurations. Unexpected profiles occur in the EIT spectra. We have found the degenerate Zeeman sublevels are responsible for these profiles. The experimental data are in good agreement with the results from the theoretical calculation which takes into account all the 13 Zeeman levels in the Lambda system. Our study demonstrates that Zeeman sublevels play important roles in quantum interference phenomena such as EIT and amplification without population inversion (AWI), and should be taken into account in the analysis of these phenomena.

Chen, YC, Simien CE, Laha S, Gupta P, Martinez YN, Mickelson PG, Nagel SB, Killian TC.  2004.  Electron screening and kinetic-energy oscillations in a strongly coupled plasma, Dec 31. Physical Review Letters. 93 AbstractWebsite

We study equilibration of strongly coupled ions in an ultracold neutral plasma produced by photoionizing laser-cooled and trapped atoms. By varying the electron temperature, we show that electron screening modifies the equilibrium ion temperature. Even with few electrons in a Debye sphere, the screening is well described by a model using a Yukawa ion-ion potential. We also observe damped oscillations of the ion kinetic energy that are a unique feature of equilibration of a strongly coupled plasma.

Chen, YC, Liao YA, Chiu HY, Su JJ, Yu IA.  2001.  Observation of the quantum interference phenomenon induced by interacting dark resonances, Nov. Physical Review A. 64:5., Number 5 AbstractWebsite

We report an experimental observation of narrow and high-contrast spectra. which are induced by interacting dark resonances and have been predicted in Phys. Rev. A 60, 3225 (1999). Spectra are measured with cold (87)Rb atoms produced by a magneto-optical trap. In this experimental system, a coupling laser and a weak probe laser form a three-level Lambda -type configuration of electromagnetically induced transparency (EIT); a microwave drives a magnetic-dipole transition between the fourth level and the ground state that is coupled with the excited state by the coupling laser. The observed spectral profile of probe absorption exhibits a very sharp peak emerging inside a narrow EIT dip. Such spectral feature provides more opportunities in manipulating atomic-optical response.

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)
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.

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Guan, WY, Chen YC, Wei JYT, Xu YH, Wu MK.  1993.  ION-SIZE EFFECT ON T(M) AND T(C) IN (R1-XPR(X))BA2CU3O7 SYSTEMS (R = YB, TM, ER, HO, DY, GD, EU, SM, ND AND Y), Apr. Physica C-Superconductivity and Its Applications. 209:19-22., Number 1-3 AbstractWebsite

The magnetic ordering temperatures T(m) of Pr ions in (R1-xPrx)Ba2Cu3O7 systems (R = Yb, Tm, Er, Ho, Dy, Gd, Eu, Sm, Nd and Y) with x = 0.5 - 1.0 were measured. We observe that T(m) decreases monotonically with increasing R concentration. At constant x, T(m) is R ion-size dependent. The slope in the T(m) vs. x is steeper for ion with smaller ionic radius. In comparison with the ion-size effect on the superconducting transition temperatures T(c) in these systems, the observed results can be qualitatively interpreted in terms of the hybridization between the local states of Pr ion and the conduction band states of the CuO2 planes.

Guan, WY, Xu YH, Sheen SR, Chen YC, Wei JYT, Lai HF, Wu MK, Ho JC.  1994.  ION-SIZE EFFECT ON TN IN (R1-XPRX)BA2CU3O7-Y SYSTEMS (R=LU, YB, TM, ER, Y, HO, DY, GD, EU, SM, AND ND), Jun 1. Physical Review B. 49:15993-15999. AbstractWebsite

We conducted a detailed study of the structure and magnetic properties of (R1-xPrx)Ba2Cu3O7 sintered samples, where R = Lu, Yb, Tm, Er, Y, Ho, Dy, Gd, Eu, Sm, and Nd for x = 0.5-1.0. We found that the temperature dependence of the dc susceptibility follows the Curie-Weiss law in the temperature range 20-300 K and the paramagnetism of the Pr and R sublattices exist independently of one another. The antiferromagnetic ordering temperature T(N) of Pr ions decreases monotonically with increasing R concentration (1-x). At a given x, T(N) is R-ion-size dependent. The slope in the T(N) vs x curve is steeper for ions with smaller ionic radii. The observed results are interpreted in terms of the hybridization between the local states of the Pr ion and the valence-band states of the CuO2 planes.

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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.

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)
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)
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.