Macroscopic quantum dynamics of pi-junctions with ferromagnetic insulators

TL;DR

This paper presents a theoretical study of macroscopic quantum behavior in pi-junctions with ferromagnetic insulators, proposing a qubit with high coherence and minimal dissipation effects.

Contribution

It introduces a new model for a pi-junction qubit based on superconductor-ferromagnetic insulator structures, highlighting its potential for high-coherence quantum computing.

Findings

Proposes a pi-junction qubit with spontaneous two-level systems.

Shows quasiparticle dissipation has negligible impact on quantum tunneling.

Demonstrates potential for high-coherence quantum devices.

Abstract

We theoretically investigate the macroscopic quantum dynamics of a pi junction with a superconductor (S) and a multiferroic material or a ferromagnetic insulator (FI). By deriving the effective action from a microscopic Hamiltonian, a pi-junction qubit (a S-FI-S superconducting quantum interference device ring) is proposed. In this qubit, a quantum two-level system is spontaneously generated and the effect of the quasiparticle dissipation is found to be very weak. These features make it possible to realize a quiet qubit with high coherency. We also investigate macroscopic quantum tunneling (MQT) in current-biased S-FI-S pi junctions and show that the influence of the quasiparticle dissipation on MQT is negligibly small.