Coupling a single electron spin to a microwave resonator: Controlling transverse and longitudinal couplings

TL;DR

This paper proposes a method to strongly couple a single electron spin in a quantum dot to a microwave resonator using a nanomagnet, enabling high-fidelity quantum state transfer and controllable coupling types.

Contribution

It demonstrates realistic coupling strengths, controllable coupling types, and methods to mitigate decoherence, advancing the integration of electron spins with microwave quantum circuits.

Findings

Estimated spin-resonator coupling of ~1 MHz with realistic parameters.

Showed precise placement allows switching between longitudinal and transverse coupling.

Achieved >90% fidelity in coherent state transfer.

Abstract

Microwave-frequency superconducting resonators are ideally suited to perform dispersive qubit readout, to mediate two-qubit gates, and to shuttle states between distant quantum systems. A prerequisite for these applications is a strong qubit-resonator coupling. Strong coupling between an electron-spin qubit and a microwave resonator can be achieved by correlating spin- and orbital degrees of freedom. This correlation can be achieved through the Zeeman coupling of a single electron in a double quantum dot to a spatially inhomogeneous magnetic field generated by a nearby nanomagnet. In this paper, we consider such a device and estimate spin-resonator couplings of order ~ 1 MHz with realistic parameters. Further, through realistic simulations, we show that precise placement of the double dot relative to the nanomagnet allows to select between a purely longitudinal coupling (commuting with the bare spin Hamiltonian) and a purely transverse (spin non-conserving) coupling. Additionally, we suggest methods to mitigate dephasing and relaxation channels that are introduced in this coupling scheme. This analysis gives a clear route toward the realization of coherent state transfer between a microwave resonator and a single electron spin in a GaAs double quantum dot with a fidelity above 90%. Improved dynamical decoupling sequences, low-noise environments, and longer-lived microwave cavity modes may lead to substantially higher fidelities in the near future.