Quantum thermodynamics with a single superconducting vortex

Abstract

We demonstrate complete control over dynamics of a single superconducting vortex in a nanostructure which we coin the Single Vortex Box (SVB). Our device allows us to trap the vortex in a field-cooled aluminum nanosquare and expel it on demand with a nanosecond pulse of electrical current. We read-out the vortex state of the box by testing the switching current of the adjacent Dayem nanobridge. Using the time-resolving nanothermometry we measure 4$\cdot$10$^{-19}\,$J as the amount of the dissipated heat (which is the energy of a single red photon) in the elementary process of the vortex expulsion, and monitor the following thermal relaxation of the device. The measured heat is equal to the energy required to annihilate all Cooper pairs on the way of the moving vortex. Our design and measuring protocol are convenient for studying the stochastic mechanism of the vortex escape from current-driven superconducting nanowires, which has its roots either in thermal or quantum fluctuations, similar to ones widely studied in Josephson junctions or magnetic nanoclusters and molecules. Our experiment enlightens the thermodynamics of the absorption process in the superconducting nanowire single-photon detectors, in which vortices are perceived to be essential for a formation of a detectable hot spot. The demonstrated opportunity to manipulate a single superconducting vortex reliably in a confined geometry comprises in fact a proof-of-concept of a nanoscale non-volatile memory cell with sub-nanosecond write and read operations, which offers compatibility with quantum processors based either on superconducting qubits or rapid single flux quantum circuits.