Detecting virtual photons in ultrastrongly coupled superconducting quantum circuits

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä

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2024-01

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en

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15
1-15

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PHYSICAL REVIEW RESEARCH, Volume 6, issue 1

Abstract

Light-matter interaction and understanding the fundamental physics behind is essential for emerging quantum technologies. Solid-state devices may explore new regimes where coupling strengths are "ultrastrong", i.e., comparable to the energies of the subsystems. New exotic phenomena occur the common root of many of them being the fact that the entangled vacuum contains virtual photons. They herald the lack of conservation of the number of excitations which is the witness of ultrastrong coupling breaking the U(1) symmetry. Despite more than a decade of research, the detection of ground-state virtual photons still awaits demonstration. In this work, we recognize the "conspiring"set of experimental challenges and show how to overcome them, thus providing a solution to this long-standing problem. We find that combining a superinductor-based unconventional "light fluxonium"qudit and coherent control yields a highly efficient, faithful, and selective conversion of virtual photons into real ones. This enables their detection with resources available to present-day quantum technologies.

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Funding Information: We acknowledge F. Deppe, V. Villari, G. Chiatto, and G. Anfuso who helped to develop key insights for this paper. We acknowledge discussions and remarks by S. De Liberato, S. Felicetti, P. Forn-Diaz, N. Roch, J. Ankerold, J. Koch, A. Ridolfo, and W. W. Huang. This work was supported by the QuantERA grant SiUCs (Grant No. 731473), by the PNRR MUR project PE0000023-NQSTI, by ICSC Centro Nazionale di Ricerca in High-Performance Computing, Big Data and Quantum Computing, by the University of Catania, Piano Incentivi Ricerca di Ateneo 2020-22, project Q-ICT. E.P. acknowledges the COST Action CA 21144 superqumap and G.S.P. acknowledges financial support from the Academy of Finland under the Finnish Center of Excellence in Quantum Technology QTF (Projects No. 312296, No. 336810, No. 352927, No. 352925). Publisher Copyright: © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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Giannelli, L, Paladino, E, Grajcar, M, Paraoanu, G S & Falci, G 2024, ' Detecting virtual photons in ultrastrongly coupled superconducting quantum circuits ', PHYSICAL REVIEW RESEARCH, vol. 6, no. 1, 013008, pp. 1-15 . https://doi.org/10.1103/PhysRevResearch.6.013008