Gauge ambiguities imply Jaynes-Cummings physics remains valid in ultrastrong coupling QED

Adam Stokes, Ahsan Nazir

    Research output: Contribution to journalArticlepeer-review


    Ultrastrong-coupling between two-level systems and radiation is important for both fundamental and applied quantum electrodynamics (QED). Such regimes are identfied by the breakdown of the rotating-wave approximation, which applied to the quantum Rabi model (QRM) yields the apparently less fundamental Jaynes-Cummings model (JCM). We show that when truncating the material system to two levels, each gauge gives a different description whose predictions vary significantly for ultrastrong-coupling. QRMs are obtained through specific gauge choices, but so too is a JCM without needing the rotating-wave approximation. Analysing a circuit QED setup, we find that this JCM provides more accurate predictions than the QRM for the ground state, and often for the
    first excited state as well. Thus, Jaynes-Cummings physics is not restricted to light-matter coupling below the ultrastrong limit. Among the many implications is that the system's ground state is not necessarily highly entangled, which is usually considered a hallmark of ultrastrong-coupling.
    Original languageEnglish
    Article number499
    JournalNature Communications
    Issue number1
    Early online date30 Jan 2019
    Publication statusPublished - 30 Jan 2019

    Research Beacons, Institutes and Platforms

    • Photon Science Institute


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