The level theory of coherence

Jan Peřina

J. H. Macek

The theory of atomic lifetime measurements is developed on the basis of the quantum theory of radiation. The effect of coherent emission on the shape of the decay curves is studied in detail. It is shown that the light intensity will oscillate in time when two closely spaced levels decay coherently. Oscillations due to interference between fine-structure levels of the hydrogen atom in particular are discussed.

Soma, Gaius

Namit Anand, Georgios Styliaris, Meenu Kumari +1 more

We establish a rigorous connection between quantum coherence and quantum chaos by employing coherence measures originating from the resource theory framework as a diagnostic tool for quantum chaos.We quantify this connection at two different levels: quantum states and quantum channels.At the level of states, we show how several well-studied quantifiers of chaos are, in fact, quantum coherence measures in disguise (or closely related to them).We further this connection for all quantum coherence measures by using tools from majorization theory.Then we numerically study the coherence of chaotic-versus-integrable eigenstates and find excellent agreement with random matrix theory in the bulk of the spectrum.At the level of channels, we show that the coherence-generating power (CGP)-a measure of how much coherence a dynamical process generates on average-emerges as a subpart of the out-of-time-ordered correlator (OTOC), a measure of information scrambling in many-body systems.Via numerical simulations of the (nonintegrable) transverse-field Ising model, we show that the OTOC and CGP capture quantum recurrences in quantitatively the same way.Moreover, using random matrix theory, we analytically characterize the OTOC-CGP connection for the Haar and Gaussian ensembles.In closing, we remark on how our coherence-based signatures of chaos relate to other diagnostics, namely, the Loschmidt echo, OTOC, and the Spectral Form Factor.

Zizhao Gan, Guozhen Yang

This paper contains the second part of a theory of the coherent propagation of a light wave in semiconductors. After considering the interaction among the electrons, we discuss the matter of the interaction of a semiconductor with light and derive equations of motion for the polarization wave of the excitons which have been excited by the light. We show how our equations can be approximated by linear ones and how the exciton polarization wave can be regarded as a Bose field in the limit of low excitation. In this paper we also discuss in detail the problem of the coherent excitation of discrete exciton levels. We show that the coherently excited discrete exciton is approximately equivalent to a two-level atom which is excited by a light wave; the atom energy-level spacing is a function of the degree of excitation, and the density of equivalent "two-level atoms" is determined by features of the exciton-state wave function.