External Coherent Field Research Articles

Signatures of the superfluid-insulator phase transition in laser-driven dissipative nonlinear cavity arrays

We analyze the nonequilibrium dynamics of a gas of interacting photons in an array of coupled dissipative nonlinear cavities when driven by a pulsed external coherent field. Using a mean-field approach, we show that the response of the system is strongly sensitive to the underlying (equilibrium) quantum phase transition from a Mott insulator to a superfluid state at commensurate filling. We find that the coherence of the cavity emission after a quantum quench can be used to determine the phase diagram of an optical many-body system even in the presence of dissipation.

Decoherence in the solvable dynamics of N strongly driven atoms coupled to a cavity mode

We present the exact solution of the dynamics of N two-level atoms strongly driven by an external coherent field and equally coupled on resonance to a cavity mode, in the presence of both cavity dissipation and atomic decay. Analytical results are presented for system and subsystem dynamics, showing how environment-induced decoherence leads the system from pure to mixed states. In the limit of negligible atomic decay, where the system is known to exhibit decoherence-free subspaces, we present a detailed discussion of the decoherence function that can be monitored by atomic population measurements.

Microscopic theory of multiple-phonon-mediated dephasing and relaxation of quantum dots near a photonic band gap

We derive a quantum theory of the role of acoustic and optical phonons in modifying the optical absorption line shape, polarization dynamics, and population dynamics of a two-level atom (quantum dot) in the ``colored'' electromagnetic vacuum of a photonic band-gap (PBG) material. This is based on a microscopic Hamiltonian describing both radiative and vibrational processes quantum mechanically. We elucidate the extent to which phonon-assisted decay limits the lifetime of a single photon-atom bound state and derive the modified spontaneous emission dynamics due to coupling to various phonon baths. We demonstrate that coherent interaction with undamped phonons can lead to an enhanced lifetime of a photon-atom bound state in a PBG. This results in reduction of the steady-state atomic polarization but an increase in the fractionalized upper state population in the photon-atom bound state. We demonstrate, on the other hand, that the lifetime of the photon-atom bound state in a PBG is limited by the lifetime of phonons due to lattice anharmonicities (breakup of phonons into lower energy phonons) and purely nonradiative decay. We also derive the modified polarization decay and dephasing rates in the presence of such damping. This leads to a microscopic, quantum theory of the optical absorption line shapes. Our model and formalism provide a starting point for describing dephasing and relaxation in the presence of external coherent fields and multiple quantum dot interactions in electromagnetic reservoirs with radiative memory effects.

Controlling the optical bistability via interacting dark-state resonances

We analyze the behavior of optical bistability in a four-level mercury atomic system driven by a cavity and two external coherent fields by means of a unidirectional ring cavity. We find that without interacting dark resonances and for large intensity of coupling field, the optical bistability disappears. So, the double dark resonances could significantly establish the optical bistability. Moreover, we demonstrate that the double dark resonances can dramatically reduce the threshold of optical bistability.

Three-mode entanglement and amplification in correlated spontaneous emission lasers

We propose a scheme for establishing three-coloured correlated spontaneous emission lasers and generating tripartite continuous-variable entanglement. The interaction of three cavity fields is formed by beating two of them in a two-channel Raman or two-photon transition and by correlating the two-mode beat and the third cavity field in the successive transitions. Using the sufficient inseparability criterion proposed by van Loock and Furusawa, we show that the three cavity fields are entangled when the numbers of photons are large and the saturation is weak. The upper limits of the photon numbers for the entanglement are dependent on the frequencies and amplitudes of the external coherent fields.

Bright entangled light from two-mode cascade laser

We show that a two-mode three-level cascade laser driven by external coherent fields generate intense entangled light. It turns out that external driving fields which are at resonance with the cavity modes substantially improve the intensity of the two-mode light in the cavity in a region where the squeezing and entanglement is significant making the system under consideration a viable source of bright squeezed as well as entangled light.

Control of spontaneous emission spectra via an external coherent magnetic field in a cycle-configuration atomic medium

Control of spontaneous emission spectra via an external coherent magnetic field in a cycle-configuration atomic medium

Transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure

The transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure is reported. The transient process of the system, which is induced by the external coherent coupling field, shows the property of no inverse gain. We find that the transient behavior of the probe field can be tuned by the change of tunneling barrier. Both the amplitude of the transient gain and the frequency of the oscillation can be affected by the lifetime broadening.

Control of spontaneous emission spectra via an external coherent magnetic field in a cycle-configuration atomic medium

We theoretically study the features of the spontaneous emission spectra in a coherently driven cold four-level atomic system with a cyclic configuration. It is shown that a few interesting phenomena such as spectral-line narrowing, spectral-line enhancement, and spectral-line suppression can be realized in our system. Interestingly enough, the spectral-line enhancement and suppression can be controlled just by appropriately modulating the phase, the frequency, and the intensity of an external coherent magnetic field, respectively. This investigation may find applications in high-precision spectroscopy.

All-optical switching and storage in a four-level tripod-type atomic system

The optical behavior of a four-level tripod-type atomic system in a ring resonator driven by a cavity field and two external coherent fields is studied. It is shown that the atomic response exhibits an ultra-sensitive switch from high absorption to nearly transparency by changing the value of one of the control fields. The optical bistable response can be controlled by means of the external fields. The system can flip from the lower to the upper branch of the hysteresis curve without changing the incident probe. Switching and information storage of a light signal are predicted under appropriate triggering of the auxiliary external optical signals.

MAXIMUM ENTANGLEMENT IN A JAYNES-CUMMINGS SYSTEM WITH STRONGLY DRIVEN ATOMS

We describe the entanglement of a Jaynes-Cummings system, where a two-level atom is also strongly driven by an external coherent field while it crosses a resonant cavity prepared in a coherent state. First we consider the atom-cavity field entanglement, described by the Von Neumann entropy. We find that it depends only on the interaction time and the initial atomic state. The entropy vanishes in the case of maximally polarized atom, independent of the interaction time, whereas it reaches its maximum value for atom in the upper or lower state and for long enough interaction times. Then we investigate the entanglement between two consecutive strongly driven atoms interacting with the cavity mode assumed in the vacuum state, showing that they never entangle in spite of the existence of atom-atom correlations.

Finite-dimensional states and entanglement generation for a nonlinear coupler

We discuss a system comprising two nonlinear (Kerr-like) oscillators coupled mutually by a nonlinear interaction. The system is excited by an external coherent field that is resonant to the frequency of one of the oscillators. We show that the coupler evolution can be closed within a finite set of $n$-photon states, analogously as in the nonlinear quantum scissors model. Moreover, for this type of evolution our system can be treated as a Bell-like state generator. Thanks to the nonlinear nature of both oscillators and their internal coupling, these states can be generated even if the system exhibits its energy dissipating nature, contrary to systems with linear couplings.

Quantum entanglement in a system of two spatially separated atoms driven by an external coherent laser field

We study quantum entanglement between two spatially separated atoms driven by an external coherent laser field in the dissipative process of spontaneous emission. It is shown that the entanglement exhibits long-time oscillatory behaviour with remarkable entanglement in the peaks and the peak and period are related to the Rabi frequencies of the external coherent laser field.

Eigenenergies and wave functions of the Tavis-Cummings system driven by an external classical coherent field

We study the interaction of the atoms in the two-atom Tavis-Cummings (T-C) model under an external classical driving field. The eigenenergies - quasienergies and eigenstates of the T-C system driven by the external field are calculated i n the interaction picture. We also give the general wave function of the system in the Schrdinger picture. We show that the driving field does not change the energy levels of the T-C model, but makes the Fock states displaced. A stationar y state with a definite frequency in the normal two-atom T-C model is transform ed into the Fock states with infinite frequencies by the driving field.

Amplification without population inversion in a three-level Λ-type system with an external coherent magnetic field

In this Letter, we investigate the amplification without inversion (AWI) in a new scheme, a three-level Λ-type system which the two lower states are coupled by an external magnetic field. We find that, owing to the presence of the external magnetic field, the absorption of the probing field is very sensitive to the relative phase of the probing and the pumping fields. By appropriately choosing the Rabi frequency of the pumping field, the Lamor frequency of the external magnetic field and the relative phase, AWI can be realized.

Intensity–intensity correlations in a V-type atom driven by a coherent field in a broadband squeezed vacuum

We study the intensity–intensity correlation in a closely spaced doublet V-type three-level atom driven by an external coherent field and damped by ab roadband squeezed vacuum. We are interested in the manner in which the atom emits photons under the combined effect of quantum interference and squeezed vacuum .F or distinguishable photons an dd egenerate transitions, the squeezed field produces anticorrelation, whereas for nondegenerate transitions the effect of the squeezed field is the surpassing of the antibunching during certain time intervals. We find that bunching/antibunching behaviour and the symmetry of the two emission processes can be controlled by the relative phase of the squeezed vacuum to the coherent field. For particular conditions we show a bunching behaviour which turns to antibunching when the two-photon correlations in the squeezed vacuum are reduced to the classical level. Therefore, this transition must be attributed to the quantum nature of the squeezed vacuum. We also study the sideband correlations. We find that squeezed vacuum makes the sidebands evolve at different rates which are phase dependent.

Squeezing spectra in a V-type three-level atom interacting with a broadband squeezed field

We investigate the effect of quantum interference in the phase-dependent spectra of a V-type three-level atom where both transitions from the upper states to the lower state are driven by a single coherent field. In addition, the atom is damped by a broadband squeezed field. We are particularly interested in the role of the vacuum induced coherence on the spectrum of quantum fluctuations in phase quadratures of resonance fluorescence. We find that in some circumstances, the combined effect of the squeezed field and the vacuum induced coherence (VIC) can significantly modify the nonclassical behavior of the system. In particular, it is possible to enhance the squeezing in marked contrast with the case where the atom is damped by the standard vacuum. The squeezing spectrum can be modified by changing the relative phase of the squeezed vacuum to the external coherent field.

Micromaser spectrum and phase diffusion dynamics

We discuss a scheme to relate the phase diffusion dynamics of the micromaser field to the measured atomic population statistics. This can allow us to measure the linewidth of the micromaser spectrum and to solve a relevant decoherence problem in cavity quantum electrodynamics. The main steps are (i) a suitable preparation of the cavity field state to generate coherences, (ii) the transfer of information on the dynamics of field coherences to probe atoms by the action of an external resonant coherent field and (iii) the derivation of the phase diffusion rate, hence the micromaser linewidth, from the measured population statistics of the probe atoms. The method can be applied even in the presence of trapping states, wher ep eculiar linewidth oscillations are expected for increasing pump rate, due to the quantum nature of the micromaser field.

Interaction and stability of periodic and localized structures in optical bistable systems

We analytically and numerically study the role of the homogeneous zero mode on the interaction between two modulational instabilities. Periodic and localized structures (LSs) are considered in two transverse dimensions. We consider a real-order parameter description for a passive optical cavity driven by an external coherent field, valid close to the onset of optical bistability. A global description of pattern formation in both monostable and bistable regimes is given. We show that the interaction between the modulational modes and the zero mode modifies the existence and the stability of diffractive patterns. In particular, this interaction induces a coexistence between two different types of phase locked hexagonal structures. We also consider the interaction between two separated LSs. An analytical expression for the interaction potential in terms of modified Bessel functions is derived. Numerical simulations confirm the analytical predictions.

Cavity Steady-State Behaviors for a Single Equidistant Three-Level Emitter

The interaction of a single equidistant three-level radiator (same transition frequencies, dipole moments, and decay rates for both one-photon transitions) with a leaky optical cavity mode that at the same time is driven by an external coherent field is investigated via a generalized Fokker–Planck equation. It is shown that the steady-state behaviors of such an equidistant three-level sample differ from the corresponding ones of a general three-level system. We suppose that this difference appears due the fact that a single equidistant three-level radiator is equivalent to a pair of indistinguishable two-level atoms, provided that the separation between the pair is smaller than the wavelength of the cavity field.