Cyclic Superconducting Quantum Refrigerators Using Guided Fluxon Propagation

TL;DR

This paper introduces a novel quantum refrigeration method using guided fluxon propagation in type-II superconductors, offering potential for on-chip cooling and improved quantum device performance.

Contribution

It proposes a cyclic quantum refrigeration cycle utilizing fluxons in a superconductor with detailed thermodynamic characterization and practical figures of merit.

Findings

Achieves estimated cooling power of 10 nW/mm².

Demonstrates potential for on-chip micro-refrigeration below dilution refrigerator temperatures.

Shows enhancement of quantum circuit coherence and detector efficiency.

Abstract

We propose cyclic quantum refrigeration in solid-state, employing a gas of magnetic field vortices in a type-II superconductor -- also known as fluxons -- as the cooling agent. Refrigeration cycles are realized by envisioning a racetrack geometry consisting of both adiabatic and isothermal arms, etched into a type-II superconductor. The guided propagation of fluxons in the racetrack is achieved by applying an external electrical current, in a Corbino geometry, through the sample. A gradient of magnetic field is set across the racetrack allowing one to adiabatically cool down and heat up the fluxons, which subsequently exchange heat with the cold, and hot reservoirs, respectively. We characterize the steady state of refrigeration cycles thermodynamically for both $s-$wave and $d-$wave pairing symmetries, and present their figures of merit such as the cooling power delivered, and the coefficient of performance. Our cooling principle can offer significant cooling for on-chip micro-refrigeration purposes, by locally cooling below the base temperatures achievable in a conventional dilution refrigerator. We estimate $10\mathrm{nW}/\mathrm{mm}^2$ of cooling power per unit area under typical operating conditions. Integrating the fluxon fridge to quantum circuits can enhance their coherence time by locally suppressing thermal fluctuations, and improve the efficiency of single photon detectors and charge sensors.