Lasing at half the Josephson frequency with exponentially long coherence times

TL;DR

This paper introduces a superconducting device that produces laser light at half the Josephson frequency with exponentially long coherence times by using multiple emitters, overcoming previous limitations of spontaneous switching.

Contribution

It develops a general model for a half-Josephson laser with many emitters, demonstrating conditions for exponentially long coherence times surpassing traditional laser limits.

Findings

Coherence times can be exponentially extended in the proposed device.

Large fluctuation analysis explains switching behavior and coherence limits.

Conditions for stable, long-lived laser operation are identified.

Abstract

We describe a superconducting device capable of producing laser light in the visible range at half the Josephson generation frequency, with the optical phase of the light locked to the superconducting phase difference. An earlier proposed device, the so called "half-Josephson laser" [Phys. Rev. Lett. 107, 073901 (2011)], cannot provide long coherence times, because of spontaneous switchings between the emitter states. To circumvent this we consider N >> 1 emitters driving an optical resonator mode. We derive a general model that captures essential physics of such devices while not depending on specific microscopic details. We find the conditions under which the coherence times are exponentially long, thus surpassing the fundamental limitation on the coherence times of common lasers. For this we study the noise in the device. In particular, we are interested in the rate of large fluctuations of the light field in the limit where the typical fluctuations are small. The large fluctuations are responsible for switching of the laser between stable states of radiation and therefore determine the coherence time.