# Multiplexed readout of four qubits in 3D cQED architecture using broadband JPA

## TL;DR

This paper demonstrates a frequency-multiplexed readout scheme for four qubits in a 3D cQED architecture, utilizing a broadband parametric amplifier for high-fidelity, scalable quantum measurement.

## Contribution

It introduces a novel multiplexed readout method with broadband amplification, enabling scalable and efficient qubit measurement in 3D cQED systems.

## Key findings

- Achieved high-fidelity single-shot readout of four qubits
- Implemented broadband parametric amplification with 380 MHz bandwidth
- Demonstrated scalable multiplexed readout architecture

## Abstract

We propose and demonstrate a frequency-multiplexed readout scheme in 3D cQED architecture. We use four transmon qubits coupled to individual rectangular cavities which are aperture-coupled to a common rectangular waveguide feedline. A coaxial to waveguide transformer at the other end of the feedline allows one to launch and collect the multiplexed signal. The reflected readout signal is amplified by an impedance engineered broadband parametric amplifier with 380 MHz of bandwidth. This provides us high fidelity single-shot readout of multiple qubits using compact microwave circuitry, an efficient way for scaling up to more qubits in 3D cQED.