# Single-sideband modulator for frequency domain multiplexing of superconducting qubit readout

## TL;DR

This paper presents a superconducting single-sideband modulator that enables efficient frequency domain multiplexing for qubit readout, operating with purely reactive elements and no microwave control tones.

## Contribution

It introduces a novel cryogenic-compatible single-sideband modulator using reactive components, enhancing multiplexing capabilities for superconducting qubit systems.

## Key findings

- Operates in 4-8 GHz band with up to -85 dBm power.
- Converts signals by up to 120 MHz in frequency.
- Suppresses spurious harmonics by up to 25 dB.

## Abstract

We introduce and experimentally characterize a superconducting single-sideband modulator compatible with cryogenic microwave circuits, and propose its use for frequency domain multiplexing of superconducting qubit readout. The monolithic single-quadrature modulators that comprise the device are formed with purely reactive elements (capacitors and Josephson junction inductors) and require no microwave-frequency control tones. Microwave signals in the 4 to 8 GHz band, with power up to -85 dBm, are converted up or down in frequency by as much as 120 MHz. Spurious harmonics in the device can be suppressed by up to 25 dB for select probe and modulation frequencies.