Coherence Window in the dynamics of Quantum Nanomagnets

TL;DR

This paper identifies a narrow magnetic field region in nanomagnetic insulators where decoherence is significantly reduced, enhancing the potential for quantum coherence in solid-state qubits.

Contribution

It demonstrates a specific field regime that drastically lowers decoherence rates in nanomagnetic systems, supported by calculations for various materials.

Findings

Decoherence can be reduced by over 6 orders of magnitude in certain field regions.

The results impose limits on observing macroscopic quantum coherence in magnetic systems.

A narrow field window exists where phonon and nuclear spin decoherence are minimized.

Abstract

Decoherence in many solid-state systems is anomalously high, frustrating efforts to make solid-state qubits. We show that in nanomagnetic insulators in large transverse fields, there can be a fairly narrow field region in which both phonon and nuclear spin-mediated decoherence are drastically reduced. As examples we calculate decoherence rates for the $Fe$-8 nanomolecule, for $Ni$ particles, and for $Ho$ ions in $LiHo_xY_{1-z}F_4$. The reduction in the decoherence, compared to low field rates, can exceed 6 orders of magnitude. The results also give limitations on the observability of macroscopic coherence effects in magnetic systems.