Quantum behavior of the dc SQUID phase qubit

TL;DR

This paper investigates a dc SQUID phase qubit design, analyzing its quantum behavior, isolation capabilities, and potential for non-destructive readout through numerical solutions of its Hamiltonian.

Contribution

It provides a detailed analysis of a dc SQUID phase qubit with an isolation junction, including eigenstates, energy levels, and tunneling rates, highlighting its potential for improved qubit isolation and readout.

Findings

The system's Hamiltonian was numerically solved to find eigenstates and energy levels.

The isolation junction's current expectation value depends on the qubit state.

The design can enable non-destructive qubit state readout.

Abstract

We analyze the behavior of a dc Superconducting Quantum Interference Device (SQUID) phase qubit in which one junction acts as a phase qubit and the rest of the device provides isolation from dissipation and noise in the bias leads. Ignoring dissipation, we find the two-dimensional Hamiltonian of the system and use numerical methods and a cubic approximation to solve Schrodinger's equation for the eigenstates, energy levels, tunneling rates, and expectation value of the currents in the junctions. Using these results, we investigate how well this design provides isolation while preserving the characteristics of a phase qubit. In addition, we show that the expectation value of current flowing through the isolation junction depends on the state of the qubit and can be used for non-destructive read out of the qubit state.