Coherence and multimode correlations from vacuum fluctuations in a microwave superconducting cavity

TL;DR

This paper demonstrates that double parametric pumping of a superconducting microwave cavity can generate tunable coherence between photons in different frequency modes, originating from vacuum fluctuations and stimulated by quantum processes.

Contribution

It introduces a novel method to produce and control coherence between separate frequency modes via vacuum fluctuations in a superconducting cavity.

Findings

Vacuum fluctuations can induce coherence between different frequency modes.

Double parametric pumping enables tunable phase-controlled correlations.

Quantum fluctuations stimulate simultaneous creation of photon pairs.

Abstract

The existence of vacuum fluctuations is one of the most important predictions of modern quantum field theory. In the vacuum state, fluctuations occurring at different frequencies are uncorrelated. However, if a parameter in the Lagrangian of the field is modulated by an external pump, vacuum fluctuations stimulate spontaneous downconversion processes, creating squeezing between modes symmetric with respect to half of the frequency of the pump. Here we show that by double parametric pumping of a superconducting microwave cavity, it is possible to generate another fundamental type of correlation, namely coherence between photons in separate frequency modes. The coherence correlations are tunable by the phases of the pumps and are established by a quantum fluctuation that stimulates the simultaneous creation of two photon pairs. Our analysis indicates that the origin of this vacuum-induced coherence is the absence of 'which-way' information in the frequency space.