Front-induced frequency shifting of microwave pulses in Travelling-Wave Parametric Amplifiers

The energy of a light quantum can be changed by modulating its environment in time, an effect which is dubbed photon energy lifting. We temporally vary the propagation velocity of a microwave pulse inside a Travelling-Wave Parametric Amplifier (TWPA) by means of a counterpropagating current front. This modulation of the microwave pulse gives rise to a frequency shift, which depends solely on the current front amplitude. Naturally, this amplitude-dependent frequency conversion preserves the microwave pulse shape and does not generate any harmonics and practically no intermodulation products. In this contribution, we will show experimental evidence of front-induced microwave frequency shifting. This technique of linearly shifting microwave pulses holds promise for practical applications in quantum computing and quantum sensing. Furthermore, these findings open avenues for further research in the field of non-linear optics in superconducting microwave devices.