Abstract
We have created a doubly tunable resonator, with the intention to simulate relativistic motion of the resonator boundaries in real space. Our device is a superconducting coplanar-waveguide microwave resonator, with fundamental resonant frequency ω1/(2π) ~ 5 GHz. Both of its ends are terminated to ground via dc-SQUIDs, which serve as magnetic-flux-controlled inductances. Applying a flux to either SQUID allows the tuning of ω1/(2π) by approximately 700 MHz. Using two separate on-chip magnetic-flux lines, we modulate the SQUIDs with two tones of equal frequency, close to 2ω1. We observe photon generation, at ω1, above a certain pump amplitude threshold. By varying the relative phase of the two pumps we are able to control this threshold, in good agreement with a theoretical model. At the same time, some of our observations deviate from the theoretical predictions, which we attribute to parasitic couplings resulting in current driving of the SQUIDs.
Highlights
Vacuum is commonly considered to be empty space
The superconducting quantum interference device (SQUID) inductance can be modulated either by flux pumping, through Φac, which is a direct modulation of the resonator boundary condition and the analogue of a moving mirror, or by ac driving the SQUID current Is
The SQUIDs are made of aluminium and deposited by two-angle evaporation, while the rest of the circuit is etched in niobium
Summary
In quantum theory, it contains vacuum fluctuations of the electromagnetic field Due to these fluctuations, two perfectly conducting mirrors at rest, placed in close vicinity of each other, can exhibit radiation pressure forces, known as the Casimir effect [1]. The physical conditions equivalent to a mirror moving at about 1/4 of the speed of light can be created [5] This is done by placing a superconducting quantum interference device (SQUID) at the end of a transmission line. The SQUID inductance can be modulated either by flux pumping, through Φac, which is a direct modulation of the resonator boundary condition and the analogue of a moving mirror, or by ac driving the SQUID current Is. The generation of DCE photons using a flux-pumped SQUID at the end of a transmission line was suggested in Ref. The generation of DCE photons using a flux-pumped SQUID at the end of a transmission line was suggested in Ref. [6] and demonstrated in Ref. [7]
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