Order and chaos in the world of atoms

G. P. Berman, Alexander Iomin

Graham P. Collins

Graham P. Collins

Jean-Gabriel Hartmann, Murugan, Jeff, Shock, Jonathan P.

Quantum small-worlds are quantum many-body systems that interpolate between completely ordered (nearest-neighbour, next-to-nearest-neighbour etc.) and completely random interactions. As such, they furnish a novel new laboratory to study quantum systems transitioning between regular and chaotic behaviour. In this article, we introduce the idea of a quantum small-world network by starting from a well understood integrable system, a spin-1 Heisenberg chain. We then inject a small number of long-range interactions into the spin chain and study its ability to scramble quantum information using two primary devices: the out-of-time-order correlator (OTOC) and the spectral form factor (SFF). We find that the system shows increasingly rapid scrambling as its interactions become progressively more random, with no evidence of quantum chaos.

Santhosh Ganapa

We will discuss various aspects of thermalization, chaos and hydrodynamics in one dimensional classical Hamiltonian systems. We study two problems. First, we will revisit the Fermi-Pasta-Ulam-Tsingou (FPUT) problem in order to understand what thermalization is and discuss what leads the system starting from a typical initial condition to a thermal state. Here we discuss the various possibilities like the role of averaging, the choice of observables, the choice of initial conditions and the role of chaos in thermalization. Then, we study the evolution of a blast wave in an alternate mass hard particle (AHP) gas and study the evolution of conserved fields in the system at short times. We find a good agreement with the Taylor-von Neumann-Sedov (TvNS) solution, which was studied during the Second World War in the context of atomic explosions, everywhere except near the core of the blast. We then model this behaviour by using the Navier-Stokes-Fourier (NSF) equations.