We investigate the quantum-mechanical state of motion of an atom strongly coupled to an optical cavity. The atomic motion is coupled to the environment through cavity decay and this leads to nonclassical effects due to the dissipative evolution. The scheme is examined as an atomic position measurement and the symmetry of the cavity field mode is found to lead to Schr\"odinger cat states of the motion in the selective evolution.
We investigate the quantum-mechanical state of motion of an atom strongly coupled to an optical cavity. The atomic motion is coupled to the environment through cavity decay and this leads to nonclassical effects due to the dissipative evolution. The scheme is examined as an atomic position measurement and the symmetry of the cavity field mode is found to lead to Schr"odinger cat states of the motion in the selective evolution.
Schrödinger cat states, representing coherent superpositions of macroscopically distinguishable states, are indispensable nonclassical resources for continuous-variable quantum information processing. Existing generation protocols typically rely on strong nonlinear interactions, complicated control techniques, or engineered dissipation, posing challenges for experimental implementation. Here, we propose a simple measurement-based protocol for generating Schrödinger cat states in a cavity-QED system by combining coherent driving, dispersive atom--cavity interactions, and atomic postselection. The atom--cavity interaction establishes coherent correlations between the atomic and photonic degrees of freedom, while the subsequent atomic postselection projects the cavity field onto a non-Gaussian superposition state with pronounced Wigner negativity. Numerical simulations based on the Lindblad master equation show that the generated Schrödinger cat states remain robust against moderate cavity dissipation. Our results demonstrate that conditional atomic measurements provide an effective and experimentally accessible approach for preparing nonclassical cavity states without relying on strong optical nonlinearities or engineered dissipation.
In a recent publication [K. Hammerer, M. Wallquist, C. Genes, M. Ludwig, F. Marquardt, P. Treutlein, P. Zoller, J. Ye, and H. J. Kimble, Phys. Rev. Lett. 103, 063005 (2009)] we have shown the possibility to achieve strong coupling of the quantized motion of a micron-sized mechanical system to the motion of a single trapped atom. In the proposed setup the coherent coupling between a SiN membrane and a single atom is mediated by the field of a high finesse cavity and can be much larger than the relevant decoherence rates. This makes the well-developed tools of cavity quantum electrodynamics with single atoms available in the realm of cavity optomechanics. In this article we elaborate on this scheme and provide detailed derivations and technical comments. Moreover, we give numerical as well as analytical results for a number of possible applications for transfer of squeezed or Fock states from atom to membrane as well as entanglement generation, taking full account of dissipation. In the limit of strong-coupling the preparation and verification of nonclassical states of a mesoscopic mechanical system is within reach.
We measure the quantum speed of the state evolution of the field in a weakly driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment-assisted speed-up is realized: the quantum speed of the state repopulation in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms).
The nonclassical properties of light and atomic dynamics are studied. The system considered are two level atom interact with a quantized field in a high quality cavity, which is recognized as the Jaynes-Cumming Model. The time- and intensity-dependent atom-field coupling are applied to the system, with different initial field states and initial atomic states. We also extend the system for three level atom in a cavity, and include the dissipative mechanism in the system. We consider the laser driven three level atom in a cavity coupled to a reservoir. Interesting effects of the transient coupling are analyzed through the collapse-revival pattern in population inversion, while the nonclassicality of cavity field is studied through the features in the evolution ofWigner function. The inversion of initial superposed atomic state seems to be independent of initial classical fields but can be stimulated by the Schrodinger cat field. In two level system, the oscillatory coupling coefficient can prolong the occurrence of collapse, in analogy to the Zeno effect.The intensity atom-field coupling duration is an important parameter for controlling atomic inversion and producing frozen nonclassical light in the cavity after the atom-field coupling ceases. The theory developed will provide useful physical insights for future experimental work and enhance significant knowledge on the nonclassicality of light in matter-wave interaction. The research results will particularly benefit quantum information technology.
In the quantum trajectory approach an open quantum system is represented by a stochastic pure-state wave function. The mixed-state density operator that satisfies the usual master equation is recovered from the quantum trajectories by performing either an ensemble average or, for stationary systems, an average over time. This unraveling of the master equation dynamics into pure-state trajectories provides new insight into the decay of quantum coherence in systems that are open to the environment. Under some conditions macroscopic superposition states are preserved as macroscopic superposition states along individual trajectories, but are reduced to mixtures by the trajectory average. Under other conditions one of the states in a macroscopic superposition becomes dominant (in amplitude) over the other along each quantum trajectory. We discuss the mechanisms that produce these dynamics and assess the implications for the observation of Schrodinger cat states in optics experiments. We present results for some specific examples of macroscopic superposition states generated by a cavity QED system. The system involves a small collection of atoms in an optical cavity driven by a coherent laser field. Under strong-coupling conditions this system produces a variety of Schrodinger cat states whose precise form depends on the number of atoms, the method of excitation (through a cavity mirror or from the side), the initial state of the atoms, and the position of the atoms in the cavity.
by Mambwe Mumba We examine a system comprised of a single two-level atom inside a driven optical cavity.We allow for cavity decay and atomic spontaneous emission out the side of the cavity.There is a spatial dependent coupling between the atom and the cavity mode, which we take into account, using explicit trapping potentials for the atom.Previous work has revolved around a harmonic oscillator potential, we also find here a solution for a realistic optical lattice potential when the lattice wavelength is half the driving laser wavelength.Atomic and cavity detunings are included, as well as effective Franck-Condon factors.Analytic results are obtained for various intensity-intensity and field-intensity correlation functions, using quantum trajectory theory in the weak driving field limit.Nonclassical effects are obtained, and we investigate the effect of a nonstationary atom on these effects.These result from violation of inequalities that must be satisfied if there is an underlying classical stochastic field; violations imply that there is no well defined electric field at all times, with some underlying positive definite probability distribution.The center of mass wave function is specified either by a list of probability amplitudes, or these amplitudes are calculated from an explicit wave function(typically a Gaussian).The correlation functions are quite sensitive to the center of mass wave function, and perhaps correlation functions can be used as probes of atomic motion.We also examine a new inequality between intensity-intensity and field intensity correlation functions, that is violated here.