# Korshunov instantons in a superconductor at elevated bias current

## TL;DR

This paper investigates Korshunov instantons in superconductors under high bias current, revealing a new tunneling regime with quadratic current dependence, which could facilitate experimental observation.

## Contribution

It introduces a novel high-bias current regime with a different tunneling rate scaling, expanding understanding of quantum tunneling in superconducting systems.

## Key findings

- Identifies a new tunneling regime with $I^2$ scaling.
- Shows elevated bias current enhances tunneling rate.
- Proposes experimental verification of Korshunov instantons.

## Abstract

Dissipation even at zero temperature reduces quantum fluctuations and tends to localize particles. A notable exception is the nonlinear dissipation due to quasiparticle tunneling in a Josephson junction. It is well known that quasiparticle dissipation does not prevent the phase particle in a superconducting junction to coherently tunnel to the next-nearest minimum even though tunneling to the nearest minimum is suppressed. The reason is that the dissipative action admits an instanton solution, the so-called Korshunov instanton. Here, we analyze this model at elevated bias current $I$. We find that besides the known regime where the logarithm of the tunneling rate scales as $I^{2/3}$ there is novel regime with a scaling $I^2$. We argue that the novel regime opens an opportunity for an experimental verification of the Korshunov instantons as the elevated bias current leads to a larger tunneling rate compared to earlier results.