Excitation Of Quantum Systems Research Articles

Excitation of quantum systems by short laser pulses: The effect of the pulse shape and durations

We present a simple universal approach for the description of the quantum system excitation by short laser pulses in terms of the probability during the action of a pulse. Our attention is focused on the probability dependence on the pulse duration for different pulse envelopes and detunings of the carrier from the resonance frequency. We considered Gaussian, super-Gaussian, sin2 and rectangular envelopes and a Gaussian spectral profile of the excitation cross section. It is shown that the excitation probability as a function of the pulse duration is of various characters, changing from monotonic to oscillating depending on a pulse shape, a carrier frequency detuning from the resonance, and a spectral width of the cross section, in contrast to the prediction of the standard perturbation approach based on the Fermi golden rule.

Domain-wall dynamics in Bose-Einstein condensates with synthetic gauge fields.

Interactions in many-body physical systems, from condensed matter to high-energy physics, lead to the emergence of exotic particles. Examples are mesons in quantum chromodynamics and composite fermions in fractional quantum Hall systems, which arise from the dynamical coupling between matter and gauge fields1,2. The challenge of understanding the complexity of matter-gauge interaction can be aided by quantumsimulations, for which ultracold atoms offer a versatile platform via the creation of artificial gauge fields. An important step towards simulating the physics of exotic emergent particles is the synthesis of artificial gauge fields whose state depends dynamically on the presence of matter. Here we demonstrate deterministic formation of domain walls in a stable Bose-Einstein condensate with a gauge field that is determined by the atomic density. The density-dependent gauge field is created by simultaneous modulations of an optical lattice potential and interatomic interactions, and results in domains of atoms condensed into two different momenta. Modelling the domain walls as elementary excitations, we find that the domain walls respond to synthetic electric field with a charge-to-mass ratio larger than and opposite to that of the bare atoms. Our work offers promising prospects to simulate the dynamics and interactions of previously undescribed excitations in quantum systems with dynamical gauge fields.

Envelope Area and Electric Pulse Area Interference in Excitation of Quantum Systems by Few-Cycle Attosecond Light Pulses

Envelope Area and Electric Pulse Area Interference in Excitation of Quantum Systems by Few-Cycle Attosecond Light Pulses

Perturbations of the excited quantum oscillator: From number states to statistical distributions

We discuss the transitions that an external time-dependent perturbation can induce upon a quantum harmonic oscillator in an excited initial state. In particular, we show how to describe transitions of the oscillator from initial states characterized by statistical distributions. These results should be useful for interpretations of the properties of weakly dispersive bosonic excitations in quantum systems whose dynamics is investigated by time or energy resolved spectroscopies.

High-frequency excitation of quantum systems with adiabatic nonlinearity

The excitation by a high-frequency field of multi-level quantum systems with a slowly varying density of states is investigated. This class of systems includes hydrogen-like atoms, surface electrons in metals, charge bubbles in liquid helium and other bound systems. It is found that the excitation takes place through a ladder of sharp quasi-resonances, whose shape is universal, namely independent of the driving-field parameters and of the details of the system. The amplitudes of these peaks satisfy a system-dependent tight-binding equation in energy space. Two classes of examples are considered in detail: for a particle in a positive power-law potential well, the amplitudes exhibit a local crossover in energy between a regime of exponential decay and an asymptotic power-law tail, which depends on the field parameters. For a negative power-law potential well, exponential localization, similar to the Anderson localization in a finite lattice, is found. The localization length depends on the field parameters as well as on the specific power of the potential well. The two classes contain, as special cases, the `bubble' model and the one-dimensional hydrogen atom; previous results are confirmed for these cases, and new results are presented.

Graphic method of calculating echo-response parameters under conditions of multipulse excitation of quantum systems

Multipulse excitation of systems is widely used in nonlinear spectroscopy. In high-resolution NMR spectroscopy of solids excitation by a succession of many pulses makes it possible to substantially suppress resonance line broadening. Such sequences are used in echo-spectroscopy, making it possible to obtain a more informative or the same response as with a signal of a two-pulse echo. Therefore it is important to predict theoretically the action of multipulse system excitation. This article presents an approach for obtaining faster and more complete information on the generating signals. Comparing the responses with graphically determined elements, by the shape of the latter the author finds formation times, wave vectors, and complex amplitudes of signals; he determines their dependence on reversible T/sub 2/ and irreversible T/sub 1/, T/sub 2/ phase relaxation times, as well as on spectral diffusion processes. By means of the given method the author succeeded in finding pulse sequences leading to response generation with new dependences on cross sections of the exciting pulses.