Regensburg 2022 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 4: Many-Body Quantum Dynamics 1 (joint session DY/TT)
TT 4.7: Talk
Monday, September 5, 2022, 11:45–12:00, H20
Observation of phase synchronization and alignment during free induction decay of quantum spins with Heisenberg interactions — •Jürgen Schnack1, Heinz-Jürgen Schmidt2, Christian Schröder3, and Patrick Vorndamme1 — 1Universität Bielefeld — 2Universität Osnabrück — 3Fachhochschule Bielefeld
Equilibration of observables in closed quantum systems that are described by a unitary time evolution is a meanwhile well-established phenomenon apart from a few equally well-established exceptions. Here we report the surprising theoretical observation that integrable as well as non-integrable spin rings with nearest-neighbor or long-range isotropic Heisenberg interaction not only equilibrate but moreover also synchronize the directions of the expectation values of the individual spins (New J. Phys. 23 (2021) 083038). We highlight that this differs from spontaneous synchronization in quantum dissipative systems. In our numerical simulations, we investigate the free induction decay (FID) of an ensemble of up to N = 25 quantum spins with s = 1/2 each by solving the time-dependent Schrödinger equation numerically exactly. Our findings are related to, but not fully explained by conservation laws of the system. The phenomenon very robust against for instance random fluctuations of the Heisenberg couplings. Synchronization is not observed with strong enough symmetry-breaking interactions such as the dipolar interaction and is also not observed in closed-system classical spin dynamics.