Dynamics Of Population Inversion Research Articles

Quantum effects induced by two classical fields in a coherent cavity field containing two two-level atoms

The paper derives an exact solution for a two-qubit system coupling to a quantized cavity field driven by two different types of external fields when the cavity is initially in a coherent field state. The two-qubit quantum coherence via the Jensen–Shannon divergence and the two-qubit entanglement via the negativity are investigated under the effects of the physical parameters. The results are depicted that, the generated two-qubit effects depend on the external-qubit and the external-field detunings as well as the initial cavity coherent intensity. It is found that the increase of the parameters of the initial coherent states, the detuning between the cavity field and the external classical field, and the detuning between the qubit and the external classical fields are played a key role in the dynamics of the population inversion and the generated entropic qubit-cavity entanglement. The oscillation amplitudes of the atomic population can be improved when the classical-field detuning is equal to the qubit detuning, and they can be weakened dramatically when the qubit detuning is smaller than the classical-field detuning. The qubit-cavity entanglement can be improved when the classical-field detuning is larger than the qubit detuning, and vice versa. • An exact solution is derived for a two-qubit system coupling to a quantized cavity field driven by two different types of external fields. • Dynamics of population inversion and generated entropy qubit-cavity entanglement are explored under the initial states as well as the detunings. • Two-qubit quantum coherence via the Jensen–Shannon divergence and the two-qubit entanglement via the negativity are investigated.

Dynamics of entanglement and population inversion of two qubits in a hybrid nonlinear system

An analytical solution is obtained when the Kerr medium and Stark shift are considered as nonlinear interaction terms to the system containing two-qubit and two-mode electromagnetic field from the parametric amplifier. Dynamics of the population inversion, cavity–qubit and qubit–qubit entanglements are analyzed under the unitary cavity–qubit interaction, the Kerr medium and the Stark shift. The population inversion of a qubit presents periodic revivals and collapses. The results show that the entanglement and the population inversion as well as the inversion have the same stable intervals, that is, the collapse intervals. It is found that the Kerr medium and the Stark shift may lead to reduction of the periods and the amplitudes of the population inversion and the cavity–qubit/qubit–qubit entanglement. The deteriorated qubit–qubit/cavity–qubit entanglement and the population inversion, due to the Kerr medium, may be increased by increasing the Stark shift and vice versa.

Two-photon adiabatic passage in ultracold Rb interacting with a single nanosecond, chirped pulse

A semiclassical, four-level model of a nanosecond, chirped pulse interacting with all optically accessible hyperfine states in an ultracold alkali atom, e.g., the 85Rb, is analyzed aiming at population inversion within 5S1/2 electronic state. The nature of two-photon adiabatic passage performed by a single pulse having the bandwidth prior to chirping significantly narrower than the hyperfine splitting of 5S1/2 state is investigated in the framework of the dressed state picture. It is shown that two dressed states are involved in the adiabatic dynamics of population inversion. The excited state manifold appeared to play an important mediating role in the mechanism of population transfer.

Ultrashort Pulse Interaction with Intersubband Transitions of Semiconductor Quantum Wells

We study coherent ultrashort pulse propagation in a two-subband system in a symmetric semiconductor quantum well structure, performing calculations beyond the rotating wave approximation and the slowly varying envelope approximation and taking into account the effects of electron-electron interactions. The interaction of the quantum well structure with the electromagnetic fields is studied with modified, nonlinear, Bloch equations. These equations are combined with the full-wave Maxwell equations for the study of pulse propagation. We present results for the pulse propagation and the population inversion dynamics in the quantum well structure for different electron sheet densities.

Effect of the time-dependent coupling on a superconducting qubit-field system under decoherence: Entanglement and Wehrl entropy

The dynamics of a superconducting (SC) qubit interacting with a field under decoherence with and without time-dependent coupling effect is analyzed. Quantum features like the collapse–revivals for the dynamics of population inversion, sudden birth and sudden death of entanglement, and statistical properties are investigated under the phase damping effect. Analytic results for certain parametric conditions are obtained. We analyze the influence of decoherence on the negativity and Wehrl entropy for different values of the physical parameters. We also explore an interesting relation between the SC-field entanglement and Wehrl entropy behavior during the time evolution. We show that the amount of SC-field entanglement can be enhanced as the field tends to be more classical. The studied model of SC-field system with the time-dependent coupling has high practical importance due to their experimental accessibility which may open new perspectives in different tasks of quantum formation processing.

Effect of thermal noise on atom-field interaction: Glauber-Lachs versus mixing

Coherent signal containing thermal noise is a mixed state of radiation. There are two distinct classes of such states, a Gaussian state obtained by Glauber-Lachs mixing and a non-Gaussian state obtained by the canonical probabilistic mixing of thermal state and coherent state. Though both these versions are noise-included signal states, the effect of noise is less pronounced in the Glauber-Lachs version. Effects of these two distinct ways of noise addition is considered in the context of atom-field interaction; in particular, temporal evolution of population inversion and atom-field entanglement are studied. Quantum features like the collapse-revivals in the dynamics of population inversion and entanglement are diminished by the presence of thermal noise. It is shown that the features lost due to the presence of thermal noise are restored by the process of photon-addition.

Geometric Phase of Mixed States in the Resonance Fluorescence Spectrum

Berry phase of mixed state is investigated for modified Bloch equation with constant terms, which was used to explain sidebands in the spectrum of fluorescent light. The results show that for the physical phenomenon of sidebands, the Berry phases under the quasicyclic evolution exhibit as a geometric phase transition, where the transition point and region depend fully on the dynamics of population inversion and mixed degree. We find that, furthermore, the transition position is correlated to photon number. Thus the open quantum system preserves indeed a memory of its evolution in terms of the Berry phase, which may provide another clue for looking for devices of quantum memory in terms of geometric sideband approach.

Local field effects on population dynamics in a driven quantum dot system: general initial conditions§

The effects of local fields, due to electron–hole dipole–dipole interactions, on the excitonic population dynamics of a quantum dot system are studied. The system interacts resonantly with a continuous wave electromagnetic field. We present analytical solutions of the nonlinear optical Bloch equations for any initial condition. We also thoroughly investigate the dynamics of population inversion of the system and show that effects such as extended Rabi oscillations, self-trapping in the initial state and symmetry-breaking can occur. §This paper is dedicated to Professor Sir Peter L. Knight on the occasion of his 60th birthday and in recognition of his important contributions in the field of quantum optics, quantum information and intense laser–matter interactions.

Generalization of the Rabi population inversion dynamics in the sub-one-cycle pulse limit

We consider the population inversion in a two-level system generated by a sub-one-cycle pulse excitation. Specifically, we explore the effect that the time derivative of the pulse envelope has on the Rabi dynamics. Our analysis is based on a combination of analytical, perturbative, and nonperturbative treatments and is complemented by numerical simulations. We find a shortening of the Rabi inversion period and show that complete inversion is unobtainable under resonant, ultrashort pulse conditions. The impact of nonresonant and carrier-envelope phase-dependent effects on the dynamics of two-level and multilevel systems is studied numerically, and conditions for complete population inversion are derived.

Chaotic dynamics in erbium-doped fiber ring lasers

Chaotically oscillating rare-earth-doped fiber ring lasers (DFRLs) may provide an attractive way to exploit the broad bandwidth available in an optical communications system. Recent theoretical and experimental investigations have successfully shown techniques to modulate information onto the wide-band chaotic oscillations, transmit that signal along an optical fiber, and demodulate the information at the receiver. We develop a theoretical model of a DFRL and discuss an efficient numerical simulation which includes intrinsic linear and nonlinear induced birefringence, both transverse polarizations, group velocity dispersion, and a finite gain bandwidth. We analyze first a configuration with a single loop of optical fiber containing the doped fiber amplifier, and then, as suggested by Roy and VanWiggeren, we investigate a system with two rings of optical fiber---one made of passive fiber alone. The typical round-trip time for the passive optical ring connecting the erbium-doped amplifier to itself is 200 ns, so $\ensuremath{\approx}{10}^{5}$ round-trips are required to see the slow effects of the population inversion dynamics in this laser system. Over this large number of round-trips, physical effects like GVD and the Kerr nonlinearity, which may appear small at our frequencies and laser powers via conventional estimates, may accumulate and dominate the dynamics. We demonstrate from our model that chaotic oscillations of the ring laser with parameters relevant to erbium-doped fibers arises from the nonlinear Kerr effect and not from interplay between the atomic population inversion and radiation dynamics.

Coherence control using the ratio of Rabi frequencies for complete coherent inversion in a four-level λ system

For the purpose of an examination of coherence control, we study the dynamics of population inversion in the four-level λ system where initial populations are arbitrary coherently distributed in two lower levels. It is shown that the coherence control, which causes population transfer between the lower levels to be forbidden, is possible by using the ratio of Rabi frequencies. Under this condition, it is remarkable that the adiabatic following and the optimal detuning methods are useful to invert the four-level system completely, and it is shown that the two-photon coherences of the coupled three-level ladders are dispersive and absorptive in the former and the latter methods, respectively. From the geometrical interpretation, the Bloch vectors, describing the four-level inversions, could be defined as ones in a two-level system.

Dynamical model of Nd:LiNbO/sub 3/ waveguide lasers

The aim of this work is to investigate theoretically the dynamical characteristics of Nd:LiNbO/sub 3/ waveguide lasers. A novel theoretical model to describe the laser dynamics has been developed and implemented; it has the capability to take into account the transversal dynamics of the population inversion, represented with a transversal orthogonal function expansion, and the longitudinal gain saturation effects due to the pump absorption and to the population inversion dynamics. The Nd-doped LiNbO/sub 3/ waveguide laser has been considered pumped in the 814 nm wavelength region. The model has been compared with the available experimental data. Results are presented in various operation conditions.

Alternate time scale in multimode lasers.

We analyze the intensity fluctuation of multimode lasers by extending the linear-response theory of McCumber for single-mode lasers. In the two-mode case, we prove analytically that the rate equations allow for an additional dynamical oscillation frequency associated with the antiphase motion. This explains the self-organized collective behavior of two-mode lasers, i.e., that the total output behaves just like a single-mode laser. The linear stability predicts the scaling law for this time scale, which results quite generally through cross-saturation dynamics of population inversion. Experimental results in two different laser systems confirm these predictions.

Quasistable state of an amplifying medium with an infinite energy store

An analysis was made of the dynamics of population inversion and photon field density in an amplifying medium enclosed in a totally reflecting cavity and characterized by fast inversion switching. A dimensionless parameter D representing the stability of this medium is introduced. It is shown that the self-excitation delay in the D1 case results in retention of the initial stored energy density for a finite time governed by the specific gain, whereas in the D < 1 case the influence of self-excitation can be ignored.