Frequency-tunable generation of a shaped microwave photon using a fixed-frequency transmon

A scalable quantum computer will likely require quantum communication between remote chips. Itinerant microwave photons in a coaxial cable are a promising medium for implementing such a communication scheme [1]. To achieve high-fidelity communication, the frequency and shape of the microwave photon should be precisely controlled. In the previous study, frequency-tunable elements were used to control the waveform of the photon. In contrast, we demonstrate the frequency-tunable generation of a shaped microwave photon without using frequency-tunable elements. By changing the frequency of the drive pulse that stimulates the emission of the photon, we tune the photon frequency in the range of the linewidth of a resonator that couples to the qubit. We confirm that the emitted photon is in the desired superposition state by performing a quantum state tomography using quadrature measurements assisted by a quantum-limited parametric amplifier. Our work provides a technique without additional flux lines to tune circuit frequencies, which leads to hardware-efficient quantum communication.

[1] P. Kurpier et al., Nature 558, 264 (2018)