Quantum two-level systems in Josephson junctions as naturally formed qubits

TL;DR

This paper explores the potential of naturally occurring two-level systems in Josephson junctions to serve as qubits, offering a new approach to superconducting quantum computing with long coherence times and controllable operations.

Contribution

It demonstrates that TLSs in Josephson junctions can be used as qubits, enabling multiqubit registers and quantum gate operations within a single device.

Findings

TLSs can be used as qubits with long decoherence times

A single Josephson junction can function as a multiqubit register

Coupling between junctions allows for universal quantum gate operations

Abstract

The two-level systems (TLSs) naturally occurring in Josephson junctions constitute a major obstacle for the operation of superconducting phase qubits. Since these TLSs can possess remarkably long decoherence times, we show that such TLSs can themselves be used as qubits, allowing for a well controlled initialization, universal sets of quantum gates, and readout. Thus, a single current-biased Josephson junction (CBJJ) can be considered as a multiqubit register. It can be coupled to other CBJJs to allow the application of quantum gates to an arbitrary pair of qubits in the system. Our results indicate an alternative way to realize superconducting quantum information processing.