Quantum dynamics in a camel-back potential of a dc SQUID

TL;DR

This paper explores the quantum behavior of a superconducting circuit with a unique quadratic-quartic potential, demonstrating tunneling phenomena and identifying an optimal bias line for reduced decoherence in qubit operation.

Contribution

It introduces a novel quadratic-quartic anharmonic oscillator realized with a dc SQUID and analyzes its quantum tunneling and decoherence properties.

Findings

Good agreement with generalized double-path tunneling theory

Identification of an optimal bias line for decoherence suppression

Demonstration of potential use as a phase qubit

Abstract

We investigate the quantum dynamics of a quadratic-quartic anharmonic oscillator formed by a potential well between two potential barriers. We realize this novel potential shape with a superconducting circuit comprised of a loop interrupted by two Josephson junctions, with near-zero current bias and flux bias near half a flux quantum. We investigate escape out of the central well, which can occur via tunneling through either of the two barriers, and find good agreement with a generalized double-path macroscopic quantum tunneling theory. We also demonstrate that this system exhibits an "optimal line" in current and flux bias space along which the oscillator, which can be operated as a phase qubit, is insensitive to decoherence due to low-frequency current fluctuations.