Phase slip in a hysteretic Josephson junction. a) Real-space sketch of the phaseslip mechanism: at the instability point of the Φx(φ) relation, the phase drop φ and the screening current Is abruptly relax to smaller values, as a quantum of flux tunnels perpendicular to the Josephson junction (dark grey), releasing heat. b) Phase drop φ across the SNS junction versus applied flux to the SQUIPT, as per equation (1) with β = 10. The dashed part of the curve cannot be accessed. In a quantum phase slip (blue arrows), φ changes by slightly less than 2π. c, Potential energy of the SQUIPT as a function of φ. A local energy minimum can become unstable as the externally applied flux is changed. By macroscopic quantum tunnelling of the phase, a lower energy valley is reached, releasing an energy ΔU.

Calorimetry of a Quantum Phase Slip

Josephson junctions are a central element in superconducting quantum technology; in these devices, irreversibility arises from abrupt slips of the quantum phase difference across the junction. This phase slip is often visualized as the tunnelling of a flux quantum in the transverse direction to the superconducting weak link, which produces dissipation. Here we detect the instantaneous heat release caused by a phase slip in a Josephson junction, signalled by an abrupt increase in the local electronic temperature in the weak link and subsequent relaxation back to equilibrium. Beyond the advance in experimental quantum thermodynamics of observing heat in an elementary quantum process, our approach could allow experimentally investigating the ubiquity of dissipation in quantum devices, particularly in superconducting quantum sensors and qubits.

E. Gümüş, D. Majidi, D. Nikolić, P. Raif, B. Karimi, J. T. Peltonen, E. Scheer, J. P. Pekola, H. Courtois, W. Belzig, C. B. Winkelmann
Nat. Phys. 19, 196 (2023)