Optical Cavity Field Research Articles

Extended JC-Dicke model for two-component atomic BEC inside a cavity

We consider a trapped two-component atomic Bose-Einstein condensate (BEC), where each atom with three energy-levels is coupled to an optical cavity field and an external classical optical field as well as a microwave field to form the so-called $\Delta$-type configuration. After adiabatically eliminating the atomic excited state, an extended JC-Dicke model is derived under the rotating-wave approximation. The scaled ground-state energy and the phase diagram of this model Hamiltonian are investigated in the framework of mean-field approach. A new phase transition is revealed when the amplitude of microwave field changes its sign.

Monte Carlo study of carrier-light coupling in terahertz quantum cascade lasers

We present a method for self-consistently including the optical cavity field into Monte Carlo-based carrier transport simulations. This approach allows for an analysis of the actual lasing operation in quantum cascade lasers, considering effects such as gain, saturation, and longitudinal mode competition. Simulation results for a terahertz quantum cascade laser are found to be consistent with experiment.

Quantum dynamics of cavity-assisted photoassociation of Bose-Einstein-condensed atoms

We explore the quantum dynamics of photoassociation of Bose-Einstein condensed atoms into molecules using an optical cavity field. Inside of an optical resonator, photoassociation of quantum degenerate atoms involves the interaction of three coupled quantum fields for the atoms, molecules, and the photons. The feedback created by a high-Q optical cavity causes the cavity field to become a dynamical quantity whose behavior is linked in a nonlinear manner to the atoms inside and where vacuum fluctuations have a more important role than in free space. We develop and compare several methods for calculating the dynamics of the atom-molecule conversion process with a coherently driven cavity field. We first introduce an alternate operator representation for the Hamiltonian from which we derive an improved form of mean field theory and an approximate solution of the Heisenberg-Langevin (HL) equations that properly accounts for quantum noise in the cavity field. It is shown that our improved mean field theory corrects several deficiencies in traditional mean field theory based on expectation values of annihilation/creation operators. Also, we show by direct comparison to numerical solutions of the density matrix equations that our approximate quantum solution of HL equations gives an accurate description of weakly or undriven cavities where mean field theories break down.

Observation of strong coupling between a micromechanical resonator and an optical cavity field

Achieving coherent quantum control over massive mechanical resonators is a current research goal. Nano- and micromechanical devices can be coupled to a variety of systems, for example to single electrons by electrostatic or magnetic coupling, and to photons by radiation pressure or optical dipole forces. So far, all such experiments have operated in a regime of weak coupling, in which reversible energy exchange between the mechanical device and its coupled partner is suppressed by fast decoherence of the individual systems to their local environments. Controlled quantum experiments are in principle not possible in such a regime, but instead require strong coupling. So far, this has been demonstrated only between microscopic quantum systems, such as atoms and photons (in the context of cavity quantum electrodynamics) or solid state qubits and photons. Strong coupling is an essential requirement for the preparation of mechanical quantum states, such as squeezed or entangled states, and also for using mechanical resonators in the context of quantum information processing, for example, as quantum transducers. Here we report the observation of optomechanical normal mode splitting, which provides unambiguous evidence for strong coupling of cavity photons to a mechanical resonator. This paves the way towards full quantum optical control of nano- and micromechanical devices.

Bifurcations and bistability in cavity-assisted photoassociation of Bose-Einstein-condensed molecules

We study the photoassociation of Bose-Einstein condensed atoms into molecules using an optical cavity field. The driven cavity field introduces a dynamical degree of freedom into the photoassociation process, whose role in determining the stationary behavior has not previously been considered. The semiclassical stationary solutions for the atom and molecules as well as the intracavity field are found and their stability and scaling properties are determined in terms of experimentally controllable parameters including driving amplitude of the cavity and the nonlinear interactions between atoms and molecules. For weak cavity driving, we find a bifurcation in the atom and molecule number occurs that signals a transition from a stable steady state to nonlinear Rabi oscillations. For a strongly driven cavity, there exists bistability in the atom and molecule number.

Generation of maximally entangled mixed states of two atoms via on-resonance asymmetric atom-cavity couplings

A scheme for generating the maximally entangled mixed state of two atoms on-resonance asymmetrically coupled to a single mode optical cavity field is presented. The part frontier of both maximally entangled mixed states and maximal Bell violating mixed states can be approximately reached by the evolving reduced density matrix of two atoms if the ratio of coupling strengths of two atoms is appropriately controlled. It is also shown that exchange symmetry of global maximal concurrence is broken if and only if coupling strength ratio lies between $\frac{\sqrt{3}}{3}$ and $\sqrt{3}$ for the case of one-particle excitation and asymmetric coupling, while this partial symmetry breaking cannot be verified by detecting maximal Bell violation.

Optomechanical Entanglement between a Movable Mirror and a Cavity Field

We show how stationary entanglement between an optical cavity field mode and a macroscopic vibrating mirror can be generated by means of radiation pressure. We also show how the generated optomechanical entanglement can be quantified, and we suggest an experimental readout scheme to fully characterize the entangled state. Surprisingly, such optomechanical entanglement is shown to persist for environment temperatures above 20 K using state-of-the-art experimental parameters.

Unconditional Two-Mode Squeezing of Separated Atomic Ensembles

We propose schemes for the unconditional preparation of a two-mode squeezed state of effective bosonic modes realized in a pair of atomic ensembles interacting collectively with optical cavity and laser fields. The scheme uses Raman transitions between stable atomic ground states and under ideal conditions produces pure entangled states in the steady state. The scheme works both for ensembles confined within a single cavity and for ensembles confined in separate, cascaded cavities.

Enhanced entanglement of two atoms confined in a multi-mode optical cavity

A numerical calculation of entanglement dynamics between two non-resonant atoms interacting with a multi-mode optical cavity field has shown that the field enhances the degree of entanglement between the two atoms. Using the position of one atom of the pair as a controlling parameter, entanglement dynamics is analyzed in terms of the entanglement of formation, making a comparison with the dynamics in a single-mode cavity field. It is shown that the degree of entanglement of the present system is enhanced by the usage of multi-mode cavity and by positioning the atom closely at the node of the field mode.

Discrete teleportation protocol of continuum spectra field states

A discrete protocol for teleportation of superpositions of coherent states of optical cavity fields is presented. Displacement and parity operators are unconventionally used in Bell-like measurement for field states.

Microscopic theory of the continuous measurement of photon number.

This paper proposes a microscopic model for the continuous measurement of photon numbers where the continuous measurement is simulated by a sequence of infinitesimal processes. Each process is composed of a unitary evolution for the coupled system, which consists of the field and the measuring apparatus, followed by a projection according to the readout of the measuring apparatus. The proposed model consists of two-level atoms that are coupled one by one with an optical cavity field via the electric-dipole interaction. Each atomic level is then read out after the interaction, causing a nonunitary state reduction of the field. In particular, it is shown that this microscopic model leads to the Srinivas-Davies model that has been postulated for the photodetection process.

Full-duplex optical transmission using self-heterodyne laser transceivers

The use of semiconductor diode lasers simultaneously as heterodyne receivers and lightwave transmitters in a full-duplex single optical fiber transmission system is reported. A transmission distance of 16 km, limited by Rayleigh backscattering, is obtained at a bit rate of 40 Mb/s for this simple system, which requires no optical couplers or photodiodes. The proposed operation is analogous to that of the so-called autodyne radio receiver in which the local oscillator circuit also performs the heterodyne mixing. The optical counterpart is called a self-heterodyne mixer and offers the same frequency selectivity and tunability as a conventional heterodyne detector but with reduced receiver complexity. In the self-heterodyne receiver, an optical signal to be detected is introduced directly into the lasing cavity by coupling the signal into the laser through an uncoated cleaved end facet. Changes in the optical cavity field, which result from interference between the lasing mode and the injected signal, modulate the rate of stimulated carrier recombination and thus produce a change in the injection current. This alternating current component is detected and amplified in the laser active region bias.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>