Josephson radiation from gapless Andreev bound states in HgTe-based topological junctions

TL;DR

This paper reports direct rf emission measurements from HgTe-based topological Josephson junctions, revealing signals at half the Josephson frequency indicative of gapless Andreev bound states, which are promising for topological quantum computing.

Contribution

First direct measurement of rf emission spectra in HgTe topological Josephson junctions showing half-frequency emission linked to gapless Andreev states.

Findings

Detection of emission at half the Josephson frequency $f_J/2$

Shorter coherence time for $f_J/2$ emission line

Evidence supporting presence of topological gapless Andreev bound states

Abstract

Frequency analysis of the rf emission of oscillating Josephson supercurrent is a powerful passive way of probing properties of topological Josephson junctions. In particular, measurements of the Josephson emission enables to detect the expected presence of topological gapless Andreev bound states that give rise to emission at half the Josephson frequency $f_J$, rather than conventional emission at $f_J$. Here we report direct measurement of rf emission spectra on Josephson junctions made of HgTe-based gate-tunable topological weak links. The emission spectra exhibit a clear signal at half the Josephson frequency $f_{\rm J}/2$. The linewidths of emission lines indicate a coherence time of $0.3-\SI{4}{ns}$ for the $f_{\rm J}/2$ line, much shorter than for the $f_{\rm J}$ line ($3-\SI{4}{ns}$). These observations strongly point towards the presence of topological gapless Andreev bound states, and pave the way for a future HgTe-based platform for topological quantum computation.