Hyperfine-mediated transitions between electronic spin-1/2 levels of transition metal defects in SiC

Abstract

Transition metal defects in SiC give rise to localized electronic states that can be optically addressed in the telecom range in an industrially mature semiconductor platform. This has led to intense scrutiny of the spin and optical properties of these defect centers. For spin-1/2 defects, a combination of the defect symmetry and the strong spin–orbit coupling may restrict the allowed spin transitions, giving rise to defect spins that are long lived, but hard to address via microwave spin manipulation. Here, we show via analytical and numerical results that the presence of a central nuclear spin can lead to a non-trivial mixing of electronic spin states, while preserving the defect symmetry. The interplay between a small applied magnetic field and hyperfine coupling opens up magnetic microwave transitions that are forbidden in the absence of hyperfine coupling, enabling efficient manipulation of the electronic spin. We also find that an electric microwave field parallel to the c-axis can be used to manipulate the electronic spin via modulation of the relative strength of the dipolar hyperfine term.

An electrically driven single-atom “flip-flop” qubit

“…Electrical control of the flip-flop transition has already been used to hyperpolarize the nuclear spins of individual Cu atoms on a surface using a scanning tunneling microscope ( 43 ) and may be extended to hyperpolarize ensembles of nuclear spins using a specially designed 3D cavity as discussed here. Atoms ( 44 ) and atom-like defects ( 45 ) in SiC have strong electrical tunability of their electronic states, which may be exploited for flip-flop transitions in the presence of hyperfine-coupled nuclei. Molecular systems could permit even more tailored electrical responses ( 46 ).…”

Nuclear Spin Quantum Memory in Silicon Carbide

“…We use a z e < 0 everywhere apart from Fig. 4 For the drive we used = 1 debye [31] for all leading order transitions and estimate the transition dipole elements ˜ ∼ ∆ 1 so /∆ cr ≈ 0.002 for purely spin-orbit mixing allowed transitions. The electric field amplitudes are chosen such that all resonant Rabi frequencies are 2π •0.2 MHz; this corresponds to field strength E between 0.28 V/mm and 7.16 V/mm.…”

“…In the following we will use a dipole moment = 1 debye [31] for all leading order transitions and estimate the transition dipole elements ˜ ∼ ∆ 1 so /∆ cr ≈ 0.002 for purely spin-orbit mixing allowed transitions.…”

“…Building upon the current experiments [26][27][28][29] and nu-merical calculations [30,31], as well as using the theoretical framework we developed in previous works [32,33], in this article we identify promising qubit subsystems in TM defects and develop procedures to initialize these defects by nuclear spin polarization. The initial polarization of the nuclear spin is a prerequisite for gaining control over a selected subsystem of levels (e.g., two levels for a qubit) from the multitude of nuclear spin states.…”

An electrically-driven single-atom `flip-flop' qubit

“…The flip-flop transition has already been used to hyperpolarize the nuclear spins on individual Cu atoms on a surface using a scanning tunneling microscope [32], and may be extended to coherently con-trol the atoms' spins. Atoms [33] and atom-like defects [34] in SiC possess significant electrical tunability of their electronic states, which may be exploited for flip-flop transitions in the presence of hyperfine-coupled nuclei. Molecular systems could permit even more tailored electrical responses, as already observed in recent ensemble experiments [9].…”