# Frequency conversion in ultrastrong cavity QED

## TL;DR

This paper introduces a deterministic frequency conversion method in ultrastrong cavity QED systems, utilizing two resonators coupled to a qubit, with tunable control over photon frequency transitions.

## Contribution

It presents a novel scheme for photon frequency conversion in ultrastrong coupling regimes, enabling both single- and multiphoton processes with tunable control.

## Key findings

- The proposed system can realize versatile frequency conversion processes.
- Tuning the qubit frequency controls the resonance conditions.
- The scheme is feasible with current experimental technology.

## Abstract

We propose a new method for frequency conversion of photons which is both versatile and deterministic. We show that a system with two resonators ultrastrongly coupled to a single qubit can be used to realize both single- and multiphoton frequency-conversion processes. The conversion can be exquisitely controlled by tuning the qubit frequency to bring the desired frequency-conversion transitions on or off resonance. Considering recent experimental advances in ultrastrong coupling for circuit QED and other systems, we believe that our scheme can be implemented using available technology.