摘要:
In this paper, we present a scheme for generating continuous-variable entanglement between two spatially separated nanocavities in photonic crystals, which are mediated by a coupled-resonator optical waveguide. The entanglement degree and purity of the generated states are investigated as varying the cavity frequencies, the cavity-waveguide coupling strength, and the location of the second cavity. It is shown that a steady and pure entanglement between separated nanocavities can be generated only with a weak cavity-waveguide coupling when the cavities are resonant with the band center of the waveguide. Various cases with different cavity frequencies and coupling strengths, which affect the degree of entanglement, are also investigated, and interestingly sudden death and sudden birth of entanglement occur for strong couplings.
作者机构:
[张立辉] School of Physics and Information Engineering, Jianghan University, Wuhan 43005, China;[李高翔] School of Physical Science and Technology, Huazhong Normal University, Wuhan 430079, China
通讯机构:
[Zhang, L.-H.] S;School of Physics and Information Engineering, Jianghan University, China
作者机构:
[Tang, Zhao-hong; Li, Gao-xiang] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.;[Tang, Zhao-hong] Wuhan Inst Technol, Sch Sci, Wuhan 430073, Peoples R China.;[Ficek, Zbigniew] KACST, Natl Ctr Math & Phys, Riyadh 11442, Saudi Arabia.
通讯机构:
[Tang, Zhao-hong] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要:
We propose a scheme that is able to generate on demand a steady-state entanglement between two nondegenerate cavity modes. The scheme relies on the interaction of the cavity modes with driven two- or three-level atoms, which act as a coupler to build entanglement between the modes. We show that, in the limit of a strong driving, it is crucial for the generation of entanglement between the modes to imbalance populations of the dressed states of the driven atomic transition. In the case of a three-level V-type atom, we find that a stationary entanglement can be created on demand by tuning the Rabi frequency of the driving field to the difference between the atomic transition frequencies. The resulting degeneracy of the energy levels, together with the spontaneously generated coherence, generate a steady-state entanglement between the cavity modes. It is shown that the condition for the maximal entanglement coincides with the collapse of the atomic system into a pure trapping state. We also show that the creation of entanglement depends strongly on the mutual polarization of the transition atomic dipole moments.
摘要:
We investigate spectral properties of the atomic fluorescence and the output field of the cavity-mode of a single-atom dressed-state laser in a photonic crystal. We pay particular attention to the behavior of the spectra in the presence of the frequency dependent reservoir and search for signatures of the thresholdless lasing. Although the thresholdless behavior has been predicted by analyzing the photon statistics of the cavity field, we find that the threshold behavior still exists in the spectrum of the cavity field. We find that the structure of cavity field spectrum depends strongly on the range of the pumping rate. For low pumping rates, the spectrum is not monochromatic, it is composed of a set of discrete lines revealing the discrete (quantum) structure of the combined dressed-atom plus the cavity field system. We find that for a certain value of the pumping rate, the multi-peak structure converts into a single very narrow line centered at the cavity field frequency. A physical explanation of the behavior of the spectra is provided in terms of dressed states of the system.
作者机构:
[Li, Gao-Xiang; Zhu, Shi-Yao; Wang, Li-Gang] Chinese Univ Hong Kong, Ctr Opt Sci, Shatin, Hong Kong, Peoples R China.;[Li, Gao-Xiang; Zhu, Shi-Yao; Wang, Li-Gang] Chinese Univ Hong Kong, Dept Phys, Shatin, Hong Kong, Peoples R China.;[Zhu, Shi-Yao; Wang, Li-Gang] Zhejiang Univ, Dept Phys, Hangzhou 310027, Zhejiang, Peoples R China.;[Li, Gao-Xiang] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.;[Zhu, Shi-Yao] Hong Kong Baptist Univ, Dept Phys, Kowloon Tong, Hong Kong, Peoples R China.
通讯机构:
[Wang, Li-Gang] C;Chinese Univ Hong Kong, Ctr Opt Sci, Shatin, Hong Kong, Peoples R China.
摘要:
Motivated by the realization of the optical Dirac dispersion in the homogenous negative-zero-positive index (NZPI) material, we make a theoretical investigation on the properties of thermal emission in layered structures containing the NZPI medium. We find that when the thermal emission frequency is close to the Dirac point of the NZPI medium, the spectral hemispherical power of thermal emission in such a structure is strongly suppressed and the emission can become a high directional source with large spatial coherence.
作者机构:
[Li, Gao-xiang] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.;[Ficek, Zbigniew] KACST, Natl Ctr Math & Phys, Riyadh 11442, Saudi Arabia.;[Ficek, Zbigniew] KACST, Natl Ctr Math & Phys, POB 6086, Riyadh 11442, Saudi Arabia.
通讯机构:
[Ficek, Zbigniew] K;KACST, Natl Ctr Math & Phys, POB 6086, Riyadh 11442, Saudi Arabia.
关键词:
Entanglement;Continuous variables;Squeezed states
摘要:
Practical schemes for creation of multi-mode squeezed (entangled) states of atomic ensembles located inside a high-Q ring cavity are discussed. It is assumed that the cavity is composed of two degenerate mutually counter-propagating modes that can simultaneously couple to the atomic ensembles with the same coupling strengths. The ensembles are composed of ultra-cold atoms which are modeled as four-level systems driven by two laser fields, both co-propagating with one of the cavity directions. We illustrate a procedure that constructs multi-mode squeezed states from the vacuum by a unitary transformation associated with the collective dynamics of the atomic ensembles subjected to driving lasers of a suitably adjusted amplitudes and phases. The lasers pulses together with the cavity dissipation prepare the collective modes in a desired stationary squeezed state.
作者机构:
[Tan, Hua-tang; Li, Gao-xiang] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构:
[Tan, Hua-tang] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要:
In this paper, we investigate the generation of polychromatic quadripartite entanglement of continuous variables from a three-level Λ-type atomic system inside an optical quadruply resonant cavity. The atoms are driven by external lasers and simultaneously coupled to four cavity modes by means of multiply concurrent four-wave mixing interactions. The general master equation of the cavity field is derived explicitly. By solving the Gaussian-type master equation and using the negative-partial-transpose criterion for bipartite entanglement, we show that the genuine quadripartite entanglement of the field can be generated over a wide range of parameters. The entanglement properties of the four-mode field are discussed in detail. We find that the optimal quadripartite entanglement can be obtained when the cavity modes are tuned to be resonant with the Rabi sidebands of the driven atoms.
作者机构:
[Li, Hong-rong; Li, Fu-li] Xi An Jiao Tong Univ, Dept Appl Phys, Xian 710049, Peoples R China.;[Li, Hong-rong; Li, Fu-li] Xi An Jiao Tong Univ, Non Equilibrium Condensed Matter & Quantum Engn L, Xian 710049, Peoples R China.;[Li, Hong-rong; Li, Gao-xiang; Wang, Li-gang] Chinese Univ Hong Kong, Inst Theoret Phys, Hong Kong, Hong Kong, Peoples R China.;[Wang, Li-gang] Zhejiang Univ, Dept Phys, Hangzhou 310027, Peoples R China.;[Li, Gao-xiang] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构:
[Li, Hong-rong] X;Xi An Jiao Tong Univ, Dept Appl Phys, Xian 710049, Peoples R China.
摘要:
In this paper, we have theoretically investigated the generation of two-mode entangled states from a four-level atomic system via the Raman process. We show that the degree of entanglement between the two cavity modes could be strongly adjusted by both the Rabi frequencies and the detunings of the pumping fields. Our numerical results reveal that entanglement between the steady state of the two cavity modes depends on the difference of the two detunings of the atomic levels with the classical laser fields or the difference of the two Rabi frequencies. Finally, our result also shows that when such atomic system is operated above the threshold, it is possible to obtain the macroscopic entangled states.
摘要:
Spectral and squeezing properties of the resonance fluorescence of two coupled quantum dots forming an effective Λ-type three-level structure and connected with two normal metal leads are studied. We assume that one of the dots is driven by a strong light field and find that by modulating the bias voltage and the dot-lead coupling strengths, the electron can be selectively trapped in one of the two dressed states produced by the light field. The trapped electron possesses large coherence, and the resulting unbalanced dressed-state populations can lead to a significant enhancement or suppression of the sidebands in the resonance fluorescence spectrum. Moreover, a wideband squeezing can be generated that may be significantly enhanced by modulating the gate voltage.
通讯机构:
[Li, Gao-xiang] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
关键词:
atom lasers;microcavity lasers;optical pumping;photonic band gap;Poisson distribution;spontaneous emission
摘要:
We demonstrate the capability of complete thresholdless lasing operation between dressed states of a two-level atom located inside a microscopic cavity engineered in a photonic band-gap material. We distinguish between threshold and thresholdless behaviors by analyzing Mandel’s Q parameter for the cavity field. We find that the threshold behavior depends on whether the spontaneous emission is or is not present on the lasing transition. In the presence of the spontaneous emission, the mean photon number of the cavity field exhibits threshold behavior, indicating that the system may operate as an ordinary laser. When the spontaneous emission is eliminated on the lasing transition, no threshold is observed for all values of the pumping rate, indicating the system becomes a thresholdless laser. Moreover, we find that, under a thresholdless operation, the mean photon number can increase nonlinearly with the pumping rate, and this process is accompanied by a sub-Poissonian statistics of the field. This suggests that the nonclassical statistics can be used to distinguish a nonlinear operation of the dressed-atom laser.
摘要:
The spontaneous decay of a V-type three-level atom placed in a negative-refractive-index waveguide is analyzed. We find that in thin waveguides, highly efficient surface-guided modes are supported, which do not occur in positive-index waveguides. In addition, at low absorption, the mode density and thus spontaneous emission into particular regular-guided modes is enhanced by several orders of magnitude as compared to regular dielectric waveguides. The asymmetries between emission into the different modes and the enhancement of particular guided modes allow us to induce strong spontaneous emission interference between transitions with orthogonal transition dipole moments.
摘要:
We investigate the generation of two-mode-entangled light from a laser-driven three-level V-type atom inside a cavity by taking into account spontaneously generated quantum interference between two atomic decay channels. We show that under some conditions, the system can reduce to a nondegenerate parametric amplifier which is responsible for the entanglement between the two cavity modes. Compared to the case without the quantum interference, it is found that the entanglement of the cavity field can be significantly enhanced by the interference when the relative phase of the two pumping lasers δϕ=π.