Long-distance coupling of spin qubits via topological magnons

TL;DR

This paper proposes a method for entangling distant spin qubits using topological magnon edge states, enabling high-fidelity, fast, long-distance quantum gates with suppressed relaxation, advancing scalable quantum computing.

Contribution

It introduces a novel long-distance qubit coupling scheme via topological magnons, with a protocol achieving high fidelity and speed, and discusses suppression of relaxation effects.

Findings

Achieves 99.9% fidelity in entangling distant spin qubits.

Demonstrates a 1 MHz gate speed for long-distance coupling.

Shows suppression of qubit relaxation with antiferromagnetic coupling.

Abstract

We consider two distant spin qubits in quantum dots, both coupled to a two-dimensional topological ferromagnet hosting chiral magnon edge states at the boundary. The chiral magnon is used to mediate entanglement between the spin qubits, realizing a fundamental building block of scalable quantum computing architectures: a long-distance two-qubit gate. Previous proposals for long-distance coupling with magnons involved off-resonant coupling, where the detuning of the spin-qubit frequency from the magnonic band edge provides protection against spontaneous relaxation. The topological magnon mode, on the other hand, lies in-between two magnonic bands far away from any bulk magnon resonances, facilitating strong and highly tuneable coupling between the two spin qubits. Even though the coupling between the qubit and the chiral magnon is resonant for a wide range of qubit splittings, we find that the magnon-induced qubit relaxation is vastly suppressed if the coupling between the qubit and the ferromagnet is antiferromagnetic. A fast and high-fidelity long-distance coupling protocol is presented capable of achieving spin-qubit entanglement over micrometer distances with $1\,$MHz gate speed and up to $99.9\%$ fidelities. The resulting spin-qubit entanglement may be used as a probe for the long-sought detection of topological edge magnons.