The two Josephson junction flux qubit with large tunneling amplitude

TL;DR

This paper explores solid-state flux qubits with large tunneling amplitudes, achieved through circuit engineering, enabling potential advancements in quantum computing and detection technologies.

Contribution

It introduces a flux qubit design with high energy separation and large tunneling amplitude using low-capacitance Josephson junctions in series.

Findings

Tunneling amplitude can exceed 1K for real parameters.

Analytical instanton results match numerical solutions.

Design facilitates large-scale quantum circuit integration.

Abstract

In this paper we discuss solid-state nanoelectronic realizations of Josephson flux qubits with large tunneling amplitude between the two macroscopic states. The latter can be controlled via the height and wells form of the potential barrier, which is determined by quantum-state engineering of the flux qubit circuit. The simplest circuit of the flux qubit is a superconducting loop interrupted by a Josephson nanoscale tunnel junction. The tunneling amplitude between two macroscopically different states can be essentially increased, by engineering of the qubit circuit, if tunnel junction is replaced by a ScS contact. However, only Josephson tunnel junctions are particularly suitable for large-scale integration circuits and quantum detectors with preset-day technology. To overcome this difficulty we consider here the flux qubit with high-level energy separation between "ground" and "excited" states, which consists of a superconducting loop with two low-capacitance Josephson tunnel junctions in series. We demonstrate that for real parameters of resonant superposition between the two macroscopic states the tunneling amplitude can reach values greater than 1K. Analytical results for the tunneling amplitude obtained within semiclassical approximation by instanton technique show good correlation with a numerical solution.