A diagonalizable non-Hermitian Hamiltonian having a real spectrum may be used to define
a unitary quantum system, if one modifies the inner product of the Hilbert space properly. We …

This book explains the subtleties of quantum statistical mechanics in lower dimensions and
their possible ramifications in quantum theory. The discussion is at a pedagogical level and …

We show that the spacing distributions of rational rhombus billiards fall in a family of
universality classes distinctly different from the Wigner-Dyson family of random matrix theory …

Employing the currently discussed notion of pseudo-Hermiticity, we define a pseudounitary
group. Further, we develop a random matrix theory that is invariant under such a group and …

For N impenetrable particles in one dimension with upto next-to-nearest neighbours
interaction, we obtain the exact ground state. We establish a mapping between these N …

We explore quantum phase transitions using two probes of quantum chaos: out-of-time-
order correlators (OTOCs) and the r-parameter obtained from the level spacing statistics. In …

We suggest an extension of the Wigner surmise for the nearest-neighbor-spacing
distribution of energy levels of chaotic systems to include the n th-order spacing …

We show that quantized superconducting circuits are non-integrable at the classical level of
description, adorned by nonlinear resonances amidst stochastic sea. The stable (elliptic) …

We discuss the application of Gutzwiller's semiclassical theory to a circular billiard with a
singular magnetic flux line added at its center. The Aharonov-Bohm effect manifests itself …

We consider nearest-neighbor spacing distributions of composite ensembles of levels.
These are obtained by combining independently unfolded sequences of levels containing …