Find the upcoming seminars below.
TQM seminar #47 : June 18, 2026, 2pm (LPTMC seminar room, towers 13-12, 5th floor, room 523)
Luca Giacomelli (MPQ, UPC)
A Josephson junction in a multimode environment: emergent quantum phase transition and exact low-energy duality
The physics of a single Josephson junction coupled to a resistive environment is a long-standing fundamental problem at the center of an intense debate about the existence and properties of the superconducting-to-insulating Schmid-Bulgadaev transition. To circumvent the potential subtleties in the original derivation, we investigate the emergent criticality of a junction coupled to a multimode resonator when the number of modes is increased [1]. By solving the system via exact diagonalization, we show that at the transition point the spectrum displays universality (scale invariance) not only at low frequencies. This reflects in finite-frequency spectral signatures of the phase transition, in agreement with recent experiments. The spectrum at the critical point is successfully compared with analytical and numerical results obtained in the past [2]. Finally, we prove a low-energy exact self-duality of the model, that emerges from two different finite-size circuits with different conserved quantities [3]. This confirms and generalizes the approximate self duality that is usually invoked, and proves the independence of the transition point on the ratio of Josephson to charging energy.
[1] Giacomelli L., Ciuti C., Nature Communications, 15(1), 5455 (2024)
[2] Paris, Giacomelli, Daviet, Ciuti, Dupuis, Mora, Phys. Rev. B, 111(6), 064509 (2025)
[3] Giacomelli L., Devoret M. H., Ciuti C., Phys. Rev. Lett., 136(13), 130401 (2026)
