Quantum Chaos induces Decoherence: evidence from NMR implementation of a scaled dipolar Hamiltonian in a many-body system

CLAUDIA M. SÁNCHEZ; ANA K. CHATTAH; HORACIO M. PASTAWSKI

Easton

Conferencia; Gordon Research Conference, Quantum Science; 2018

If a magnetic polarization excess is locally injected in a crystal of interacting spins in thermal equilibrium, this ?excitation? would spread as consequence of spinspin interactions in a time scale T2. Such an apparently irreversible scrambling, known as spin diffusion, can lead the system back to ?equilibrium?. Even so, a unitary quantum dynamics would ensure a precise memory of the nonequilibrium initial condition. Then, if at a certain time, say tR, an experimental protocol reverses the many-body dynamics by changing the sign of the effective Hamiltonian, it would drive the system back to the initial state at time t. As a matter of fact, the reversal is always perturbed by small experimental imperfections and/or uncontrolled internal or environmental degrees of freedom. This limits the amount of signal recovered locally at time 2tR. The degradation accounts for these perturbations, which can also be seen as the sources of decoherence. These general ideas dene the Loschmidt echo (LE), which embodies the various time-reversal procedures implemented in nuclear magnetic resonance. For spins at high temperature we proposed the Central Hypothesis of Irreversibility, that implies that the critical perturbation vanishes in the thermodynamic limit and decoherence and irreversibility has a time scale T3 fixed by the local second moment of the unperturbed Hamiltonian.