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 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.
Highlights
The existence of vacuum fluctuations is one of the most important predictions of modern quantum field theory
For the development of quantum computing with continuous variables (CV) in microwave circuits[25], these results demonstrate that a key operation is available experimentally: two-mode squeezing[26,27] of the modes a and b, leading to a non-zero correlation habia[0]
We demonstrate that two-mode coherence correlations can be obtained from the dynamical Casimir effect by employing another fundamental quantum mechanical principle, namely the absence of which-way information[29,30], which is applied here in the frequency space
Summary
The existence of vacuum fluctuations is one of the most important predictions of modern quantum field theory. Modulated superconducting circuits have attracted significant interest[8,9,10], motivated by the demand for parametric amplifiers where the added noise is pushed to the quantum limit[11,12,13,14,15] In these systems, it has been demonstrated that vacuum fluctuations present at the input port trigger the creation of real microwave photons[16,17,18,19,20,21,22]. We demonstrate that two-mode coherence correlations can be obtained from the dynamical Casimir effect by employing another fundamental quantum mechanical principle, namely the absence of which-way information[29,30], which is applied here in the frequency space. Our approach can be generalized in a straightforward way to multiple modes and pumps, opening the way to the implementation of algorithms such as bosonic sampling[48] and the realization of CV cluster states for one-way quantum computing[49,50] in the microwave regime
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