# Microwave photon generation in a doubly tunable superconducting resonator

## TL;DR

This paper presents a superconducting resonator with tunable boundaries that can generate microwave photons through parametric modulation, demonstrating control over photon production and revealing some deviations from theoretical models.

## Contribution

The work introduces a doubly tunable superconducting resonator with dual flux control, enabling photon generation and boundary condition modulation in a novel way.

## Key findings

- Photon generation observed above a threshold pump amplitude.
- Photon production can be controlled by the relative phase of the pumps.
- Some deviations from theory are caused by parasitic couplings.

## Abstract

We have developed and tested a doubly tunable resonator, with the intention to simulate fast motion of the resonator boundaries in real space. Our device is a superconducting coplanar-waveguide half-wavelength microwave resonator, with fundamental resonant frequency ~5 GHz. Both of its ends are terminated by dc-SQUIDs, which serve as magnetic-flux-controlled inductances. Applying a flux to either SQUID allows tuning of the resonant frequency by approximately 700 MHz. By using two separate on-chip magnetic-flux lines, we modulate the SQUIDs with two tones of equal frequency, close to twice that of the resonator's fundamental mode. We observe photon generation, at the fundamental frequency, above a certain pump amplitude threshold. By varying the relative phase of the two pumps we are able to control the photon generation threshold, in good agreement with a theoretical model for the modulation of the boundary conditions. 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.