ELFT HÍRADÓ

[Szeminárium koordinátor <szfi-seminar AT wigner.mta.hu>]

WIGNER SZFI Seminar

Detecting Topological Invariants via Weak Measurements and Losses

Asbóth János
Wigner RCP SZFI

Tuesday, 12 February 2019 10:00, KFKI Campus, Bldg. 1, 2nd floor, Conference Room

Topological insulators have Hamiltonians with bulk topological invariants, which control the interesting processes at the surface of the system, but are hard to measure directly. We have found a way to measure the bulk topological invariant (winding number) of one-dimensional topological insulator Hamiltonians (with chiral symmetry): it is given by the displacement of a single particle, observed via losses[1]. Losses represent the effect of repeated weak measurements on one sublattice only, which interrupt the dynamics periodically. When these do not detect the particle, they realize negative measurements. Our repeated measurement scheme covers both time-independent and periodically driven (Floquet) topological insulators, with or without spatial disorder. In the limit of rapidly repeated, vanishingly weak measurements, it applies to non-Hermitian Hamiltonians, such as the lossy Su-Schrieffer-Heeger model[2]. Contrary to intuition, the time needed to detect the winding number can be made shorter by decreasing the efficiency of the measurement. Our scheme has since been used to measure the bulk topological invariants of a discrete-time quantum walk on photons[3].

[1] T Rakovszky, JK Asboth, and A Alberti, Phys. Rev. B 95, 201407 (2017).
[2] MS Rudner and LS Levitov, Phys. Rev. Lett. 102, 065703 (2009).
[3] X Zhan et al, Phys. Rev. Lett. 119, 130501 (2017)

 

Everyone is welcome to attend.

János Asbóth
szfi-seminar AT wigner.mta.hu