Addressing spin transitions on 209Bi donors in silicon using circularly-polarized microwaves

TL;DR

This paper demonstrates selective excitation of nearly degenerate spin transitions in bismuth donor electrons in silicon using circularly polarized microwaves, enabling precise control of qubits for quantum computing.

Contribution

It introduces a method to selectively drive spin transitions with opposite helicity using a combination of resonators to generate arbitrary microwave polarization.

Findings

Selective excitation of nearly degenerate transitions achieved

Microwave polarization control enables qubit manipulation

High sensitivity maintained with combined resonator setup

Abstract

Over the past decade donor spin qubits in isotopically enriched $^{28}$Si have been intensely studied due to their exceptionally long coherence times. More recently bismuth donor electron spins have become popular because Bi has a large nuclear spin which gives rise to clock transitions (first-order insensitive to magnetic field noise). At every clock transition there are two nearly degenerate transitions between four distinct states which can be used as a pair of qubits. Here it is experimentally demonstrated that these transitions are excited by microwaves of opposite helicity such that they can be selectively driven by varying microwave polarization. This work uses a combination of a superconducting coplanar waveguide (CPW) microresonator and a dielectric resonator to flexibly generate arbitrary elliptical polarizations while retaining the high sensitivity of the CPW.