Observation of quantum many-body effects due to zero point fluctuations in superconducting circuits

Abstract

Electromagnetic fields possess zero point fluctuations which lead to observable effects such as the Lamb shift and the Casimir effect. In the traditional quantum optics domain, these corrections remain perturbative due to the smallness of the fine structure constant. To provide a direct observation of non-perturbative effects driven by zero point fluctuations in an open quantum system we wire a highly non-linear Josephson junction to a high impedance transmission line, allowing large phase fluctuations across the junction. Consequently, the resonance of the former acquires a relative frequency shift that is orders of magnitude larger than for natural atoms. Detailed modeling confirms that this renormalization is non-linear and quantum. Remarkably, the junction transfers its non-linearity to about thirty environmental modes, a striking back-action effect that transcends the standard Caldeira-Leggett paradigm. This work opens many exciting prospects for longstanding quests such as the tailoring of many-body Hamiltonians in the strongly non-linear regime, the observation of Bloch oscillations, or the development of high-impedance qubits.

Josephson photonics with simultaneous resonances

“…where : . : indicates normal order, J p (x) is a Bessel function of the first kind of order p and ẼJ = E J e −∆ 2 /2 is the renormalised value of the Josephson energy 4,25 .…”

Josephson Photonics with Simultaneous Resonances

“…where : . : indicates normal order, J p (x) is a Bessel function of the first kind of order p and ẼJ = E J e −∆ 2 /2 is the renormalised value of the Josephson energy 4,26 .…”

Bound states in ultrastrong waveguide QED

“…(35) reduces to twice the probability found for a single qubit [Eq. (18)]. The effect of the Ising interaction is revealed at short distances where P e deviates from the single-qubit result, no longer equating to the sum of two noninteracting spins.…”

“…Trying to optimize the light-matter coupling, several experiments have reached the so-called ultrastrong coupling regime (USC) between light and a single quantum emitter, both in cavity [14,15] and waveguide QED [16][17][18]. The USC is the regime where higher-order processes than the creation (annihilation) of one photon by annihilating (creating) one matter excitation play a role.…”