Efficiency of the SQUID Ratchet Driven by External Current

TL;DR

This paper theoretically investigates the efficiency of an asymmetric superconducting quantum interference device (SQUID) driven by external currents, revealing how thermal noise and magnetic flux influence its performance and identifying conditions for maximal efficiency.

Contribution

It introduces a detailed theoretical analysis of SQUID efficiency considering thermal noise and external flux, highlighting noise-enhanced efficiency and tunability.

Findings

Efficiency depends strongly on thermal noise and magnetic flux.

Thermal noise can enhance the device efficiency.

External magnetic flux allows tuning of the SQUID's performance.

Abstract

We study theoretically the efficiency of an asymmetric superconducting quantum interference device (SQUID) which is constructed as a loop with three capacitively and resistively shunted Josephson junctions. Two junctions are placed in series in one arm and the remaining one is located in the other arm. The SQUID is threaded by an external magnetic flux and driven by an external current of both constant (dc) and time periodic (ac) components. This system acts as a nonequilibrium ratchet for the dc voltage across the SQUID with the external current as a source of energy. We analyze the power delivered by the external current and find that it strongly depends on thermal noise and the external magnetic flux. We explore a space of the system parameters to reveal a set for which the SQUID efficiency is globally maximal. We detect the intriguing feature of the thermal noise enhanced efficiency and show how the efficiency of the device can be tuned by tailoring the external magnetic flux.