Readout for Phase Qubits without Josephson Junctions

TL;DR

This paper introduces a new readout method for phase qubits that removes the need for a Josephson junction in the measurement circuitry by using capacitive coupling and microwave frequency shifts.

Contribution

It proposes a novel, junction-free readout scheme for phase qubits that simplifies the measurement setup and allows for scalable multi-qubit readout.

Findings

Eliminates the read-out SQUID in phase qubit measurement

Uses microwave frequency shifts for qubit state detection

Extensible to multiple qubits with a common readout line

Abstract

We present a novel readout scheme for phase qubits which eliminates the read-out SQUID so that the entire qubit and measurement circuitry only requires a single Josephson junction. Our scheme capacitively couples the phase qubit directly to a transmission line and detects its state after the measurement pulse by determining a frequency shift observable in the forward scattering parameter of the readout microwaves. This readout is extendable to multiple phase qubits coupled to a common readout line and can in principle be used for other flux biased qubits having two quasi-stable readout configurations.