Optical Control of Donor Spin Qubits in Silicon

TL;DR

This paper explores optical methods to control and manipulate donor spin qubits in silicon using resonant IR transitions, enabling potential advances in quantum information processing and donor-based quantum technologies.

Contribution

It introduces two optical approaches for spin-selective excitation of donor states in silicon, including calculations of transition rates and the effects of electric fields and strain.

Findings

Bi donors show the most promising optical spin polarization.

Two-photon $mbda$-transitions enable spin-selective excitation for all donors.

External electric fields or strain can facilitate spin control via optical transitions.

Abstract

We show how to achieve optical, spin-selective transitions from the ground state to excited orbital states of group-V donors (P, As, Sb, Bi) in silicon. We consider two approaches based on either resonant, far-infrared (IR) transitions of the neutral donor or resonant, near-IR excitonic transitions. For far-IR light, we calculate the dipole matrix elements between the valley-orbit and spin-orbit split states for all the goup-V donors using effective mass theory. We then calculate the maximum rate and amount of electron-nuclear spin-polarization achievable through optical pumping with circularly polarized light. We find this approach is most promising for Bi donors due to their large spin-orbit and valley-orbit interactions. Using near-IR light, spin-selective excitation is possible for all the donors by driving a two-photon $\Lambda$-transition from the ground state to higher orbitals with even parity. We show that externally applied electric fields or strain allow similar, spin-selective $\Lambda$-transition to odd-parity excited states. We anticipate these results will be useful for future spectroscopic investigations of donors, quantum control and state preparation of donor spin qubits, and for developing a coherent interface between donor spin qubits and single photons.