Interference criteria for Markov descriptions of strongly dephased quantum populations

Raqueline A. M. Santos, Renato Portugal, Marcelo Dutra Fragoso

Robert A. Indik, Rolf H. Binder, M. Mlejnek +4 more

Based on a microscopic theory of a two-band semiconductor light amplifier, we show that plasma heating, cooling, and ultrafast memory effects all act in concert to produce strong distortion of subpicosecond pulses propagating in semiconductor amplifiers. Plasma heating, spectral hole burning, and carrier density depletion are responsible for saturation of the gain seen by a propagating intense femtosecond pulse in the amplifier. Plasma cooling replenishes the carrier population on the trailing edge of the pulse, leading to pulse broadening as a consequence of gain regeneration. The inclusion of memory effects in the description of dephasing processes goes beyond the usual Markov assumption of constant dephasing rates; it significantly affects the dynamical pulse reshaping processes. \textcopyright{} 1996 The American Physical Society.

Z. I. Bezhaeva, Валерий Иустинович Оселедец

Andrea Smirne, Dario Egloff, María García Díaz +2 more

Abstract Although quantum coherence is a basic trait of quantum mechanics, the presence of coherences in the quantum description of a certain phenomenon does not rule out the possibility to give an alternative description of the same phenomenon in purely classical terms. Here, we give definite criteria to determine when and to what extent quantum coherence is equivalent to non-classicality. We prove that a Markovian multi-time statistics obtained from repeated measurements of a non-degenerate observable cannot be traced back to a classical statistics if and only if the dynamics generates coherences and subsequently turns them into populations. Furthermore, we show with simple examples that such connection between quantum coherence and non-classicality is generally absent if the statistics is non-Markovian.

Yiying Yan, Zhiguo Lü, Hang Zheng

We use an analytical method to study the dissipative dynamics of a two-level system (TLS) under a harmonic driving. The method is based on a combination of the unitary transformation and Born--Markov master-equation approach. Our main aim is to clarify the effects of counter-rotating (CR) terms of both the driving and TLS-bath (dissipative) coupling on the dynamics, in comparison with the rotating-wave results of different schemes, i.e., the well-known traditional rotating-wave approximation method, and two particular methods: one just takes into account the effects of the driving CR terms and the other the effects of the dissipative CR terms, which are derived from our general treatment. Our main results are as follows: (i) by calculating the time-dependent population difference and coherence, in the case of resonant strong driving, we demonstrate that the CR terms of both the driving and dissipative coupling play an important role in the relaxation and dephasing processes, and also the properties of the steady state; (ii) in the case of largely detuned driving, we find that the CR terms of the dissipative coupling become negligible while those of the driving contribute dominant modifications to the time evolution and steady state. Moreover, we examine the influence of the dissipation on coherent destruction of tunneling under a largely detuned strong driving. We show that an almost complete suppression of the tunneling can be achieved for a relatively long time; (iii) under certain conditions, we find numerical equivalence between one of two particular methods and the Floquet--Born--Markov approach based on exact numerical treatment of the Floquet Hamiltonian. It turns out that our method is more simple and efficient than the Floquet--Born--Markov approach for both analytical and numerical calculations. By the general comparison of different treatments we demonstrate the dynamical effects of CR terms of both the driving and the dissipative coupling on the coherence and population difference.

Clark Glymour