Magnetic adatoms as memory bits: A quantum master equation analysis

TL;DR

This paper analyzes the quantum spin dynamics of magnetic adatoms, like holmium on platinum, showing potential for long-lived single-atom memory and proposing methods for fast, high-fidelity state initialization.

Contribution

It demonstrates that quantum master equations are necessary to accurately model adatom spin dynamics and explores how environment-induced superselection influences relaxation and memory stability.

Findings

Lifetimes could surpass experimental observations under ideal conditions

Environment-induced superselection determines relaxation channels

Fast, high-fidelity state initialization is feasible within 100 ns

Abstract

Due to underlying symmetries the ground states of magnetic adatoms may be highly stable, which opens perspectives for application as single-atom memory. A specific example is a single holmium atom (with $J=8$) on a platinum (111) surface for which exceptionally long lifetimes were observed in recent scanning tunneling microscopy studies. For control and read-out the atom must be coupled to electronic contacts. Hence the spin dynamics of the system is governed by a quantum master equation. Our analysis shows that in general it cannot be reduced to a classical master equation in the basis of the unperturbed crystal-field Hamiltonian. Rather, depending on parameters and control fields, "environment induced superselection" principles choose the appropriate set of basis states, which in turn determines the specific relaxation channels and lifetimes. Our simulations suggest that in ideal situations the lifetimes should be even longer than observed in the experiment. We, therefore, investigate the influence of various perturbations. We also study the initialization process of the state of the Ho atom by applied voltage pulses and conclude that fast, high fidelity preparation, on a $100\,\text{ns}$ timescale, should be possible.