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

TL;DR

This paper demonstrates non-perturbative quantum many-body effects caused by zero point fluctuations in superconducting circuits, revealing large frequency shifts and back-action effects that surpass traditional models.

Contribution

It provides the first direct observation of non-perturbative ZPF effects in a superconducting circuit with a highly non-linear Josephson junction coupled to a high impedance line.

Findings

Resonance frequency shifts are orders of magnitude larger than in natural atoms.

Non-linearity is transferred to about 30 environmental modes.

The effects surpass the standard Caldeira-Leggett paradigm.

Abstract

Electromagnetic fields possess zero point fluctuations (ZPF) 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 ZPF 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 modelling confirms that this renormalization is non-linear and quantum. Remarkably, the junction transfers its non-linearity to about 30 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.