Two-level systems coupled to oscillators

The Journal of Chemical Physics, 1996

Multiphoton up-down-up-...͑UDU͒ excitation in a two-level system was realized under adiabatic conditions. Spectra of C 2 H 4 excitation were investigated and UDU peaks were observed. The dependence of peak amplitudes on the powers and the frequencies of exciting fields were investigated experimentally as well as by computer simulation based on the rotating wave approximation ͑RWA͒. Agreement between experimental and theoretical results was observed.

A.‑S. F. Obada, Abdullah F. Al Naim, E. M. Khalil, S. Abdel‑Khalek, and H. Eleuch, 2019

The interaction between two two-level atoms and N-level atoms (su(2) quantum system) in the non-resonance is investigated. The explicit mathematical form for the wave function is obtained. Statistical aspects, the population inversion, linear entropy, correlation function and the negativity are discussed. The influence of the number of levels and the detun-ing parameter on the population and atom-atom entanglement are studied. The results are shown that the entanglement depends crucially on the detuning.

Physical Review A, 1992

We report experimental observation of multiphoton resonances and Bloch-Siegert shifts in a strongly driven classical two-level system. The system is an optical ring resonator, and the levels are two orthogonal linear polarizations. The Rabi frequency and the Bloch-Siegert shift were measured for both the oneand three-photon cases. Satisfactory agreement was achieved with theory developed for a quantum two-level system. The experiment demonstrates that these coherence phenomena can be observed in a purely classical system.

Journal of the Optical Society of America B

We investigate the quantum dynamics of a quantum oscillator coupled with the most upper state of a three-level Λ− type system. The two transitions of the three-level emitter, possessing orthogonal dipole moments, are coherently pumped with a single or two electromagnetic field sources, respectively. We have found ranges for flexible lasing or cooling phenomena referring to the quantum oscillator's degrees of freedom. This is due to asymmetrical decay rates and quantum interference effects leading to population transfer among the relevant dressed states of the emitter's subsystem with which the quantum oscillator is coupled. As an appropriate system can be considered a nanomechanical resonator coupled with the most excited state of the three-level emitter fixed on it. Alternatively, if the upper state of the Λ−type system possesses a permanent dipole then it can couple with a cavity electromagnetic field mode which can be in the terahertz domain, for instance. In the latter case, we demonstrate an effective electromagnetic field source of terahertz photons.

The European Physical Journal D, 2010

For studying the dynamics of a two-level system coupled to a quantum oscillator we have presented an analytical approach, the transformed rotating-wave approximation, which takes into account the effect of the counter-rotating terms but still keeps the simple mathematical structure of the ordinary rotating-wave approximation. We have calculated the energy levels of ground and lower-lying excited states, as well as the time-dependent quantum dynamics. It is obvious that the approach is quite simple and can be easily extended to more complicated situation. Besides, the results are compared with the numerically exact ones to show that for weak and intermediate coupling and moderate detuning our analytic calculations are quantitatively in good agreement with the exact ones.

Physical review, 2016

We study the excitation of a two-level system (2LS) by quantum light, thereby bringing our previous studies (see part I. of this series) to a target that is quantum itself. While there is no gain for the quantum state of the target as compared to driving it with classical light, its dynamical features, such as antibunching, can be improved. We propose a chain of two-level systems, i.e., setting the emission of each 2LS as the driving source of the following one, as an arrangement to provide better single-photon sources. At a fundamental level, we discuss the notion of strongcoupling between quantum light from a source and its target, and the several versions of the Mollow triplet that follow from various types of driving light. We discuss the Heitler effect of antibunched photons from the scattered light off a laser.

arXiv preprint arXiv:0801.0310, 2008

The entanglement between a Pauli-like two-level system and a quantum harmonic oscillator enhanced by an interaction between them and a δ-pulse sequence is studied, with the decoherence due to their coupling with a Markovian bath. Without the Markovian bath, the entanglement is enhanced to maximum possible values. With the Markovian bath, the entanglement is enhanced up to some time and then dissipated, with the system in thermal equilibrium with the Markovian bath after a very long time. The time for achieving the maximum entanglement shows discontinuous jumps over the parameters of decoherence.

2010

We study a composite multimode light-two-level atom system in a cavity. We show that coupling of the two-level atom to multiple modes of the light destroys the Mott phase of the composite system thus making the system less useful platform for developing concepts in quantum information processing.

Physical Review B, 2018

Two-level system strongly coupled to a single resonator mode (harmonic oscillator) is a paradigmatic model in many subfields of physics. We study theoretically the Landau-Zener transition in this model. Analytical solution for the transition probability is possible when the oscillator is highly excited, i.e. at high temperatures. Then the relative change of the excitation level of the oscillator in the course of the transition is small. The physical picture of the transition in the presence of coupling to the oscillator becomes transparent in the limiting cases of slow and fast oscillator. Slow oscillator effectively renormalizes the drive velocity. As a result, the transition probability either increases or decreases depending on the oscillator phase. The net effect is, however, the suppression of the transition probability. On the contrary, fast oscillator renormalizes the matrix element of the transition rather than the drive velocity. This renormalization makes the transition probability a non-monotonic function of the coupling amplitude.

1997

We consider the interaction of a two-level atom inside an optical parametric oscillator. In the weak driving field limit, we essentially have an atom-cavity system driven by the occasional pair of correlated photons, or weakly squeezed light. We find that we may have holes, or dips, in the spectrum of the fluorescent and transmitted light. This occurs even in the strong-coupling limit when we find holes in the vacuum-Rabi doublet. Also, spectra with a sub-natural linewidth may occur. These effects disappear for larger driving fields, unlike the spectral narrowing obtained in resonance fluorescence in a squeezed vacuum; here it is important that the squeezing parameter N tends to zero so that the system interacts with only one correlated pair of photons at a time. We show that a previous explanation for spectral narrowing and spectral holes for incoherent scattering is not applicable in the present case, and propose a new explanation. We attribute these anomalous effects to quantum interference in the two-photon scattering of the system.