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. 

[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)

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.