Half-integer charge injection by a Josephson junction without excess noise

TL;DR

This paper investigates whether half-integer charge transfer in topological superconductor Josephson junctions can be observed as a sharp, noiseless phenomenon despite the gapless Majorana modes supporting equilibrium charge fluctuations.

Contribution

It demonstrates that out-of-equilibrium e/2 charge transfer can be nearly noiseless, and proposes a method to reduce equilibrium fluctuations for clearer detection.

Findings

Out-of-equilibrium e/2 charge transfer has vanishing excess noise.

Equilibrium charge fluctuations can be minimized using a heavy-tailed detection efficiency.

Half-integer charge transfer can be nearly noiseless with appropriate measurement strategies.

Abstract

A Josephson junction in a topological superconductor can inject a charge e/2 into a normal-metal contact, carried by chiral Majorana edge modes. Here we address the question whether this half-integer charge is a sharp observable, without quantum fluctuations. Because the Majorana modes are gapless, they support charge fluctuations in equilibrium at zero temperature. But we find that the excess noise introduced out of equilibrium by the e/2 charge transfer vanishes. We discuss a strategy to reduce the equilibrium fluctuations, by means of a heavy-tailed time-dependent detection efficiency, to achieve a nearly noiseless half-integer charge transfer.