*Speaker: *Wen Wei Ho (Harvard)
*Date:* Thursday, January 31th
*Time:* 12:00-1:00 pm
Includes Pizza.
*Title: *Quantum many-body scarring: a weak ergodicity-breaking phenomenon
*Abstract: *A central postulate of statistical mechanics is that of
ergodicity -- a generic state prepared out of equilibrium is believed to
explore its allowed phase phase and eventually thermalize. In interacting
quantum systems, known exceptions to this behavior include strongly
disordered, many-body localized (MBL) systems, and finely-tuned, integrable
systems. Recently, quench experiments with Rydberg atom arrays [Nature 551,
579 (2017)] demonstrated non-thermalizing dynamics of a new kind:
surprisingly long-lived, periodic revivals from certain simple initial
states, while quick relaxation and equilibriation from others as expected
in a quantum chaotic system. In this talk, I will show that these
observations are attributed to the presence of a small number of
exceptional, nonthermal many-body eigenstates dubbed "quantum many-body
scars" that violate the eigenstate thermalization hypothesis (ETH) [1]. I
will furthermore demonstrate that underlying the long-lived many-body
revivals is an unstable, periodic orbit, captured in a suitable variational
"semiclassical" description of the dynamics using matrix-product-states,
which suggests a possible connection to the similarly named phenomenon of
quantum scarring in single-particle quantum chaos [2]. Lastly, I will
discuss recent work on how a weak, quasilocal deformation can stabilize
revivals, leading to virtually perfect oscillations with emergent SU(2)
dynamics, and which suggests an underlying Hamiltonian with exact quantum
many-body scarring [3]. Quantum many-body scarring represents a new class
of quantum dynamics in strongly interacting systems resulting from a weak
form of ergodicity breaking, with direct experimental signatures.
Refs:
[1] Nat. Phys. *14*, 745–749 (2018)
[2] arXiv:1807.01815,
https://arxiv.org/abs/1807.01815
[3] arXiv:1812.05561,
https://arxiv.org/abs/1812.05561
*Location: *B-106 @ Center for Astrophysics (60 Garden Street
<https://maps.google.com/?q=60+Garden+Street&entry=gmail&source=g>)
*Directions: *After entering the lobby of the CfA, turn right to enter the
hallway of the B building. In the hallway, turn right again, B-106 will be
at the end of the hallway on the left side.