作者机构：
[Hu, Xiangming; Hu, Qingping; Hu, Liang; Wang, Guanghui] Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, Xiangming] C;Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Peoples R China.
摘要：
We study the nonlinearities due to direct perturbation to the dark state in coherent population trapping (CPT). To extract the susceptibilities of the CPT atoms with respect to probe fields, we treat the CPT dressing fields as control parameters and redefine susceptibilities with respect to the probe fields alone. With such a redefinition, we reveal that a CPT-based system displays an ultralarge, resonantly enhanced second-order cross susceptibility χ(2) together with vanishing linear absorption. Physically, this effect is based on the CPT dark-state shift, which is traced to the six-photon parametric processes for all involved fields (including the dressing and probe fields). Because of the lack of the direct perturbation, this effect is absent in the electromagnetically induced transparency (EIT)-based system, in which only resonantly enhanced third-order (Kerr) susceptibility χ(3) is obtainable but much weaker than the second-order one. The second-order nonlinearity, because of its stronger effect, can be more sensitive for quantum nonlinear optics at low light levels than the third-order nonlinearity.
作者机构：
[Hu, Xiangming; Wang, Chaowen; Wang, CW] Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Peoples R China.;[Wang, Chaowen; Wang, Fei] China Three Gorges Univ, Coll Sci, Yichang 443002, Peoples R China.
通讯机构：
[Wang, CW; Hu, XM; Wang, Chaowen] C;Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Peoples R China.;China Three Gorges Univ, Coll Sci, Yichang 443002, Peoples R China.
关键词：
Atomic coherence;Electromagnetically induced transparency;Quantum communications;Quantum information processing;Quantum optics;Spontaneous emission
摘要：
It is shown that the reservoir engineering can be controlled by the collective phase Phi of three coherent fields interacting with a closed Delta-type atom. We find that the atomic system acts as a one-channel dissipation reservoir when Phi = 0(pi), but it behaves as a two-channel dissipation reservoir for Phi not equal 0(pi). The phase-dependent reservoir engineering provides a convenient way to produce robust two-mode squeezing and entanglement, which may find potential applications in quantum information processing. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
作者机构：
[Hu, Xiangming; Xu, Jun; Wang, Wan] Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Hubei, Peoples R China.
通讯机构：
[Hu, Xiangming] C;Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Hubei, Peoples R China.
关键词：
Optical fields;Parametric down conversion;Photon correlations;Photon statistics;Quantum fluctuations;Spontaneous emission
摘要：
Due to either coherent or dissipative interactions with the coherent population trapping (CPT)-based atoms, the evolutions of the Bogoliubov modes towards the vacuum states have been shown to lead to second-order squeezing of the involved optical fields. Here we push the CPT-based dissipative interactions towards higher-order squeezing, which is not simply determined by second-order squeezing hut instead by different criteria involving higher-order moments, It is shown that the CPT-based atomic reservoir supports the dissipative evolution of the Bogoliubov modes almost completely to the vacuum states and then yields almost perfect fourth-order squeezing (90% similar to 100%), The present mechanism is robust against spontaneous emission since the atoms stay largely in the ground states. As a by-product, a comparison is given with two-level atoms, in which the excitation of a large fraction reduces the degree of higher-order squeezing. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
作者机构：
[Hu, Xiangming; Hu, Qingping; Hu, Liang; Wang, Guanghui] Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Hubei, Peoples R China.;[Hu, Qingping] Wuhan Text Univ, Inst Tech Phys, SEEE, Wuhan 430073, Hubei, Peoples R China.
通讯机构：
[Hu, Xiangming] C;Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Hubei, Peoples R China.
摘要：
We present a scheme to generate unitarily two-mode and four-mode field squeezing in optical cavities with the near-resonantly dressed three-level atoms in the Λ configuration. The dressing fields open two coherent population trapping (CPT) windows, within which the atoms stay predominantly in the dark state and yield strong nonlinearities for both the dressing fields themselves and the other applied fields. The two-mode squeeze operator is separated from degrees of freedom of atoms in a common CPT window, and the multimode squeeze operator is segregated in different CPT windows. The resulting two-mode and multimode interaction strengths are at least one order higher than in the previous dispersive schemes, where all fields are far off resonant with the atoms. The present near-resonant scheme is robust to spontaneous emission since atoms are nearly trapped in a long-lived superposition state.
摘要：
We show that thermal noise could play a positive role in generating one-way Einstein–Podolsky–Rosen (EPR) steering of two cavity fields dispersively interacting with a single four-level atom, each of which is independently coupled to a thermal reservoir. In the low-Q and weak Raman transition regimes, two output fields exhibit asymmetric EPR steering and the steering direction could be easily controlled by adjusting the mean photon numbers of the thermal reservoirs and the decay rates of cavities. Striking features are present in our scheme. First, one-way EPR steering is achieved by using the couplings of the cavities with the heat baths, which sheds light on the quantum state manipulation in the presence of decoherence. Second, the obtainable EPR steering occurs between the cavity fields in the low-Q regime, which relaxes the constraints on the use of good cavities and so makes our scheme more practical. Third, the correlation properties of the output modes are considered, which can be measured more conveniently and will be more applicable to implement a range of quantum information processing.
摘要：
Narrow linewidth and high intensity of the fluorescence spectra are two important elements to improve the accuracy and efficiency of related practical measurements, but so far they have not been achievable simultaneously. We propose a new approach to sharpen the linewidth and to heighten the intensity simultaneously. Rather than double coherent mechanisms, it uses the spontaneous emission of inverted atoms in a cavity below the threshold as a resource for feedback control. The spontaneous feedback is simpler in principle and easier to realize technologically, and represents a kind of new way of controlling spontaneous emission. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
作者机构：
[Hu, Xiangming; Rao, Shi; Huang, Chen; Li, Lingchao; Hu, Qingping] Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Hubei, Peoples R China.;[Hu, Qingping] Wuhan Text Univ, SEEE, Inst Tech Phys, Wuhan 430073, Hubei, Peoples R China.
通讯机构：
[Hu, Xiangming] C;Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Hubei, Peoples R China.
摘要：
There are two decisive factors for quantum correlations in reservoir engineering, but they are strongly reversely dependent on the atom-field nonlinearities. One is the squeezing parameter for the Bogoliubov modes-mediated collective interactions, while the other is the dissipative rates for the engineered collective dissipations. Exemplifying two-level atomic ensembles, we show that the moderate nonlinearities can compromise these two factors and thus enhance remarkably two-mode squeezing and entanglement of different spin atomic ensembles or different optical fields. This suggests that the moderate nonlinearities of the two-level systems are more advantageous for applications in quantum networks associated with reservoir engineering.
摘要：
We explore the asymmetric Einstein-Podolsky-Rosen (EPR) steering of field modes via atomic coherent effects. A resonant four-level system in double-cascade configuration is under our consideration, where the atoms are excited by the applied fields from one cascade channel and two cavity modes are generated from the other cascade transition. The results show two cavity modes are suitable for achieving the steady-state one-way EPR steering. We analyze the physics in terms of the dressed-atom Bogoliubov-field-mode approach. It is found that one of two Bogoliubov modes is mediated by the resonant coupling of the dressed atoms and the other is decoupled from them. This leads to the so-called one-channel dissipation, by which the dressed atoms absorb the average excitations from one transformed mode and then two original modes are pulled into the asymmetric correlation. Remarkably, the present scheme is focused on the full-resonant interaction not only between the classical fields, the cavity modes and the bare atoms, but also between the Bogoliubov modes and dressed atoms, which will induce the one-way steering simply via adjusting the intensity of an external field. Furthermore, the EPR steering could occur between the field modes with the large frequency difference, such as optical and microwave fields, which is more useful for the practical quantum communication. Based on the one-channel dissipation, the obtainable one-way EPR steering is rather against the dynamic fluctuations and is regardless of the initial state.
摘要：
We propose a theoretical method to obtain two-collective mode entanglement in a four-level atomic ensemble. One collective mode is produced due to the Raman atomic coherence, the acquisition of another collective mode is ascribed to the quantum interference in two four-wave mixing processes. We show that two-collective mode and two original single modes are also in the entangled state in experimentally accessible parameter regimes.
作者：
Rao, Shi*;Hu, Xiangming（胡响明）;Li, Lingchao;Xu, Jun
期刊：
Journal of Physics B: Atomic, Molecular and Optical Physics,2015年48(18):185501 ISSN：0953-4075
通讯作者：
Rao, Shi
作者机构：
[Hu, Xiangming; Rao, Shi; Li, Lingchao; Xu, Jun] Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Peoples R China.
通讯机构：
[Rao, Shi] C;Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Peoples R China.
关键词：
optomechanical interaction;quantum state transfer;collective interactions
摘要：
We investigate the quantum state transfer between two membranes in coupled cavities for the case before the cavity fields arrive at the steady state. Three different schemes are presented. The first one is based on the double swapping, i.e., one of the two collective cavity modes interacts with one membrane first and later with the other membrane. The second scheme is to use the mechanical dark mode, which decouples from the cavity fields and evolves adiabatically from one mechanical mode to the other. The third scheme depends on the interactions of the two oscillators with the same continuous, collective cavity mode. In comparison, the first scheme is more robust to the mechanical thermal noise, the second one depresses the cavity dissipation, and the third one merges the merits of the two former schemes.
作者机构：
[Hu, Xiangming; Rao, Shi; Li, Lingchao; Xu, Jun] Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, Xiangming] C;Cent China Normal Univ, Coll Phys Sci & Technol, Wuhan 430079, Peoples R China.
摘要：
We present a cavity dissipation scheme to prepare a hybrid system of an atomic ensemble and a moving mirror in squeezed and entangled states. This scheme is based on four-wave mixing in the atoms and radiation pressure on the mirror, both of which combine to lead to Bogoliubov interactions of the atoms and the mirror with the cavity fields. Under adiabatic conditions, the cavity fields cause the hybrid Bogoliubov modes to evolve into the vacuum states, which correspond to the two-mode squeezed and entangled states. The dependence of the hybrid entanglement on the system parameters is also presented in and beyond the Bogoliubov interactions.
