Regensburg 2025 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 12: Quantum Coherence and Quantum Information Systems (joint session TT/DY)

DY 12.4: Talk

Tuesday, March 18, 2025, 10:30–10:45, H31

Voltage without current — Christina Koliofoti and •Roman-Pascal Riwar — Peter Grünberg Institut, Forschungszentrum Jülich, 52425 Jülich, Germany

Superconductors famously give rise to equilibrium currents without voltages. But can the converse exist? We argue that voltage-dependent Josephson effects generically provide exactly such a classical time crystal behaviour -- bringing with them known conceptual issues, such as discontinuous "brick-wall" trajectories, and ill-defined canonical quantization. With the example of quantum phase slip junctions in the presence of electro-motive forces, we resolve these lingering problems. Decoherence provokes a phase transition from a quantum Hamiltonian (non-Lagrangian) system with nonlinear Cooper-pair tunneling to a Lagrangian (non-Hamiltonian) classical time crystal. Our work illustrates that direct canonical quantization of low-energy theories may fail, and that the nonadiabaticity of brick-wall trajectories leads to a temporary break down of the classical theory even for strong decoherence.

Keywords: Superconductivity; Quantum phase slips; Circuit QED; Time crystal; Josephson effect