Reconstruction of the two-mode vibronic quantum state of a trapped atom

We present a method for the direct measurement of the Wigner-function matrix for complex vibronic states of a trapped atom, that is suited to analyse the entanglement between two motional degrees of freedom and the internal electronic dynamics. It is a generalisation of the method for the determination of vibronic quantum states [S. Wallentowitz, R.L. de Matos Filho, W. Vogel, Phys. Rev. A 56, 1205 (1997)] in conjunction with the scheme for the direct observation of the Wigner function of a single motional degree of freedom [L.G. Lutterbach, L. Davidovich, Phys. Rev. Lett. 78, 2547 (1997)]. The major advantage of the present method is that it reduces the experimental efforts substantially. On the other hand, it is demonstrated that the nonlinear vibronic coupling necessary for this method turns out to be its main limitation. Received: 5 August 1998     

Review of cavity optomechanics in the weak-coupling regime: from linearization to intrinsic nonlinear interactions

Recently, cavity optomechanics has become a rapidly developing research field exploring the coupling between the optical field and mechanical oscillation. Cavity optomechanical systems were predicted to exhibit rich and nontrivial effects due to the nonlinear optomechanical interaction. However, most progress during the past years have focused on the linearization of the optomechanical interaction, which ignored the intrinsic nonlinear nature of the optomechanical coupling. Exploring nonlinear optomechanical interaction is of growing interest in both classical and quantum mechanisms, and nonlinear optomechanical interaction has emerged as an important new frontier in cavity optomechanics. It enables many applications ranging from single-photon sources to generation of nonclassical states. Here, we give a brief review of these developments and discuss some of the current challenges in this field.     

Effect of dissipative forces on the theory of a single-atom microlaser

A single-atom microlaser involving Poissonian input of atoms with a fixed flight time through an optical resonator is described. The influence of the cavity reservoir during the interactions of successive individual atoms with the cavity field is included in the analysis. Atomic decay is also considered, as it is nonnegligible in the optical regime. During the random intervals of absence of any atom in the cavity, the field evolves under its own dynamics. The steady-state characteristics of the cavity field are discussed. Away from laser threshold, the field can be nonclassical in nature.     

Factors influencing entanglement of two excitons in a coupled exciton-photon system

The relation between the excitonic purity and the concurrence in a system of two coupled large semiconduction quantum dots mediated by a single-mode cavity field is investigated by using linear entropy theory. The results show the difference in describing two modes of excitonic entanglement between linear entropy and concurrence. The relation between nonclassical property of cavity field and the entanglement degree of excitons is also discussed. The results show that two modes of exciton can reach maximal entanglement when the cavity exhibits an antibunching effect.     

Stabilization of nonclassical states of the radiation field in a cavity by reservoir engineering

We propose an engineered reservoir inducing the relaxation of a cavity field towards nonclassical states. It is made up of two-level atoms crossing the cavity one at a time. Each atom-cavity interaction is first dispersive, then resonant, then dispersive again. The reservoir pointer states are those produced by an effective Kerr Hamiltonian acting on a coherent field. We thereby stabilize squeezed states and quantum superpositions of multiple coherent components in a cavity having a finite damping time. This robust decoherence protection method could be implemented in state-of-the-art experiments.     

Statistics of discrete photodetection of resonance fluorescence in the Mollow sidebands

A method is proposed for generating conditional single-photon states with a high degree of purity in a single-mode cavity by successive discrete photodetection. The cavity is pumped by resonance fluorescence emission from a source atom driven by a classical field. The cavity is tuned to a Mollow sideband. A relation between detector parameters is found that makes it possible to interpret the detection of a probe atom in the excited state as unambiguous evidence that a pure single-photon state has been prepared in the cavity. An expression is derived for the prior probability of such an event, and dependence of the one-photon state population of the cavity field on detuning, relaxation rate, and time is examined.     

Quantum state engineering by superpositions of coherent states along a straight line with a single atomic state measurement

A new scheme is proposed for preparation of a type of nonclassical state in cavity QED. In the scheme, an atom either flying through or trapped within a cavity, is controlled by the classical Stark effect; this makes it interact alternately with a (resonant) classical field and with the (dispersive) cavity field. The cavity field, which allows an arbitrary displacement operation during the process, after the detection on the atom, finally collapses to the specific superpositions of coherent states, with their weighting factors controllable. The scheme is also applied for preparation of superpositions of motional coherent states for a trapped ion. The scheme is in contrast to all the previous ones, and thus provides a new perspective for quantum state engineering.     

Photon blockade effect in optomechanical systems

We analyze the photon statistics of a weakly driven optomechanical system and discuss the effect of photon blockade under single-photon strong coupling conditions. We present an intuitive interpretation of this effect in terms of displaced oscillator states and derive analytic expressions for the cavity excitation spectrum and the two-photon correlation function g(2)(0). Our results predict the appearance of nonclassical photon correlations in the combined strong coupling and sideband resolved regime and provide a first detailed understanding of photon-photon interactions in strong coupling optomechanics.     

Capture and release of a conditional state of a cavity QED system by quantum feedback

Detection of a single photon escaping an optical cavity QED system prepares a nonclassical state of the electromagnetic field. The evolution of the state can be modified by changing the drive of the cavity. For the appropriate feedback, the conditional state can be captured (stabilized) and then released. This is observed by a conditional intensity measurement that shows suppression of vacuum Rabi oscillations for the length of the feedback pulse and their subsequent return.     

Single-photon scattering by a Λ-type three-level in a cavity coupling to one-dimensional waveguide

The scattering of single-photon by a Λ-type three-level embedded in a cavity which is coupled to a one-dimensional waveguide is investigated theoretically by full quantum-mechanical approach. The single-photon transmission amplitude and reflection amplitude are obtained via real-space approach, respectively. It reveals that single-photon can be transmitted or reflected by controlling classic driving field tuning off or on. The effects of dissipations of the cavity and of the atom on the photon transport properties are also discussed.     

在腔场与可移动镜子系统中对镜子位置的测量

描述利用腔场与镜的相互作用,对镜的位置坐标进行测量选域以使腔场变为Fock态的叠加态.并进一步讨论其压缩特性及相干性,通过数值计算,发现该腔场有非经典效应,即有一定的压缩效应和反聚束效应.     

Conditional Detection of Fluctuations of Light from an Optical Cavity with One Atom

Fluctuations of light provide a window on the underlying quantum dynamical evolution of the source emitting light. Emission of a photon by a source signals quantum fluctuations in progress. Hence a measurement that is conditioned upon a photodetection allows us to follow the time evolution of the fluctuations and the framework of conditioned measurements provides a powerful conceptual tool for understanding nonclassical features of quantum dynamics. We discuss the connection between quantum dynamics and photon fluctuations in terms of conditional measurements of intensity and field quadratures of light from a single atom in an optical cavity. Using the Fokker- Planck equation for a single atom in a high-Q cavity, we describe the light from the cavity in terms of Gaussian random variables and a coherent component. These are used to study conditional measurements of intensity and quadrature squeezing. It is found that when the coherent component is completely removed conditional light intensity shows large fluctuations, whereas conditional squeezing exhibits strong nonclassical behavior. Indeed both field quadratures exhibit nonclassical behavior. On the other hand a small coherent component results in a sizable reduction in intensity fluctuations and small squeezing.     

Enhanced Raman Scattering by Quasi-phase-matched Processes in ax^（2） Photonic Crystal

An intense comb-shaped Raman spectra were obtained from a two-dimensional nonlinear x（2） photonic crystal - a hexagonally poled LiTaO3 crystal with lattice parameter 9 micros. The lowest Raman shift was down to 2 cm^-1 and the order of anti-stokes and stokes signals both achieved 11. The novel Raman spectra were mediated first by intense phonon-polariton fields, which were driven through the quasi-phase-matched coupling between the incident dual-beam both from an optical parametric oscillation laser, and further amplified greatly also by such quasi-phasematched nonlinear optical process. The dependence of the Raman spectra character on the wavelength and intensity of incident beams were studied in detail, which accordingly revealed information of the inelastic scattering and the elementary excitation in the nonlinear medium. These results on the other hand suggest technological importance for developing a novel Raman laser with the multi-wavelength output and a tunable frequency interval and for possible applications in quantum optics.     

INFLUENCE OF ENTANGLEMENT DEGREE ON SQUEEZING AND PHOTON ANTIBUNCHING IN THE JAYNES-CUMMINGS MODEL

We consider the case that one of entangled atoms interacts with a single-mode cavity field. The atom is selectively detected after exiting the cavity, and it is found that the nonclassical properties of field states depend strongly on the entanglement degree between the two atoms. Meanwhile it is proven that squeezing of field and photon antibunching can be greatly enhanced via selective atomic measurements.     

Photon blockade in a cavity-atom optomechanical system

We study the single-photon blockade (1PB), two-photon blockade (2PB), and photon-induced tunneling (PIT) effects in a cavity-atom optomechanical system in which a two-level atom is coupled to a single-model cavity field via a two-photon interaction. By analyzing the eigenenergy spectrum of the system, we obtain a perfect 1PB with a high occupancy probability of single-photon excitation, which means that a high-quality and efficient single-photon source can be generated. However, PIT often occurs in many cases when we consider 2PB in analogy to 1PB. In addition, we find that a 2PB region will present in the optomechanical system, which can be proved by calculating the correlation function of the model analytically.     

Faithfully probabilistic teleportation of an unknown atomic state and cavity field state with a single measurement

This paper shows that, based on the single-photon JC model depicting the resonant interaction of a two-level atom with a single cavity mode, an unknown atomic state and cavity photon superposition state can be faithfully telcported with only a single measurement. The scheme is probabilistie, its success lies on the event that the sender atom （or the medi-atom, for teleportation of cavity field state） is detected in the higher state. The scheme is in contrast to the previous ones of using a maximally two-particle entangled state as quantum channel.[第一段]     

Nondestructive Rydberg atom counting with mesoscopic fields in a cavity

We present an efficient, state-selective, nondemolition atom-counting procedure based on the dispersive interaction of a sample of circular Rydberg atoms with a mesoscopic field contained in a high-quality superconducting cavity. The state-dependent atomic index of refraction, proportional to the atom number, shifts the classical field phase. A homodyne procedure translates the information from the phase to the intensity. The final field intensity is readout by a mesoscopic atomic sample. This method opens promising routes for quantum information processing and nonclassical state generation with Rydberg atoms.     

三能级电磁感应透明中辐射场的量子统计特性

对Λ型三能级原子电磁感应透明（EIT）过程中辐射场的二阶相干度进行了研究。理论分析表明，在电磁感应透明系统中，由于原子的相干效应导致其上能级共振荧光场的二阶相干度将呈现单光子场的量子统计特性。并对其随耦合场强度和探测光失谐的变化进行了详细的分析和讨论，结果发现：在｜Ω｜〉（Γ2＋Γ3）／2情况下．采用较弱的耦合光功率（由托比频率Ω表征）及较大的探测光失谐，在较长时间延迟范围内，二阶相十度保持小于1，更利于实现非经典场的量子统计行为；相反，在｜Ω｜≤（Γ2＋Γ3）／2情况下，探测光的失谐量越小，越利于获得二阶相干度小于1的量子统计光场。南此可见选取合适的参量可优化电磁感应透明过程中单光子场的量子统计特性。     

Anabiosis of phase distribution of a three-level atom

We study the phase probability distribution of a three-level atom interacting with a cavity field in the presence of two-photon detuning and decoherence. Anabiosis of the phase probability distribution is observed due to the presence of the Stark shift. The simulation demonstrates that there is an enhancement of the phase sensitivity as soon as the two-photon detuning is considered. The W-Wigner function is also examined and it is shown that the nonclassical effect is apparent, however, for a small value of the decoherence factor.     

Generation of nonclassical light upon resonant excitation of a semiconductor microcavity

Strong correlations in the fluctuations of the intensity of emission from a semiconductor microcavity under resonant laser excitation are observed. The intensity correlation function exhibits an unusual oscillatory behavior with an unexpectedly long oscillation period and decay time. The visibility of the correlation function reaches 0.81. Long oscillation times are attributed to the Rabi frequency characterizing weak coupling between the electromagnetic field of the semiconductor microcavity mode and long-lived exciton states localized by the random potential of the quantum well. For a laser excitation power density of 400 W/cm², the power density of the radiation emitted by the microcavity is 12 W/cm², which corresponds to the total flux of nonclassical light of 1.5 × 10¹⁵ photons/s from an excited spot 50 μm in diameter. Thus, a microcavity can serve as a bright emitter of nonclassical light.