Long-lived qubit from three spin-1/2 atoms

TL;DR

This paper demonstrates that a reference-frame-free qubit constructed from three spin-1/2 atoms can maintain coherence for days, especially when using a magnetic field to suppress decoherence, making it promising for quantum memory.

Contribution

The study introduces a method to create long-lived RFF qubits from three atoms, with decoherence suppression via magnetic fields, achieving coherence times of days.

Findings

RFF qubits remain coherent under homogeneous spin conditions.

Applying a perpendicular magnetic field significantly extends qubit lifetime.

Simulations show fidelity of 0.9999 for two hours with realistic parameters.

Abstract

A system of three spin-1/2 atoms allows the construction of a reference-frame-free (RFF) qubit in the subspace with total angular momentum $j=1/2$. The RFF qubit stays coherent perfectly as long as the spins of the three atoms are affected homogeneously. The inhomogeneous evolution of the atoms causes decoherence, but this decoherence can be suppressed efficiently by applying a bias magnetic field of modest strength perpendicular to the plane of the atoms. The resulting lifetime of the RFF qubit can be many days, making RFF qubits of this kind promising candidates for quantum information storage units. Specifically, we examine the situation of three $^6\textrm{Li}$ atoms trapped in a $\textrm{CO}_2$-laser-generated optical lattice and find that, with conservatively estimated parameters, a stored qubit maintains a fidelity of 0.9999 for two hours.