Universal nonequilibrium signatures of Majorana zero modes in quench dynamics

TL;DR

This paper demonstrates a universal, robust nonequilibrium signature of Majorana zero modes in topological superconductors through quench dynamics, revealing a characteristic algebraic decay in the Loschmidt echo.

Contribution

It introduces a universal, experimentally accessible nonequilibrium signature of Majorana zero modes based on quench dynamics and Loschmidt echo decay.

Findings

Universal decay exponent of 1/4 in Loschmidt echo

Robustness of the exponent against interactions and additional channels

Potential for optical absorption measurements to detect Majorana modes

Abstract

The quantum evolution after a metallic lead is suddenly connected to an electron system contains information about the excitation spectrum of the combined system. We exploit this type of "quantum quench" to probe the presence of Majorana fermions at the ends of a topological superconducting wire. We obtain an algebraically decaying overlap (Loschmidt echo) ${\cal L}(t)=| < \psi(0) | \psi(t) > |^2\sim t^{-\alpha}$ for large times after the quench, with a universal critical exponent $\alpha$=1/4 that is found to be remarkably robust against details of the setup, such as interactions in the normal lead, the existence of additional lead channels or the presence of bound levels between the lead and the superconductor. As in recent quantum dot experiments, this exponent could be measured by optical absorption, offering a new signature of Majorana zero modes that is distinct from interferometry and tunneling spectroscopy.