Nature Materials-2020-A. Bourassa, et al.

Entanglement and control of single nuclear spins in isotopically engineered silicon carbide

Abundance Of nuclear registers

natural SiC (I = 1/2 nuclear spin):

1.1% of the carbon atoms

4.7% of silicon atoms

Strong Coupling

definition and properties

hyperfine coupling exceeds the linewidth (order 1/T2*, where T2* is the Ramsey spin dephasing time)

This strong coupling splits the ms = ±1 electronic ground state levels, which results in pairs of resolved transitions that enable direct selective control of this two-qubit state using external radio frequency (RF) magnetic fields

experiment demonstration

• isolating a single c-axis (kk) $VV^0$

• Temperature T = 5K

• a nearby $^{29}Si$ at the $Si_{IIa}$ site (parallel hyperfine $A_{//} = 2π × 13.2 MHz$)

• electron spin linewidth ($~1 MHz$)

Polarization Method

we can achieve a high initialization fidelity (~93%) as measured by the peak asymmetry in the optically detected magnetic resonance (ODMR) spectrum

three-qubit spin system

Weakly coupled nuclear memories

Why using isotopically purified sample?

Control weakly coupled spins

dependency of $\phi, \widehat{\mathbf{n}}_{0}, \widehat{\mathbf{n}}_{1}$ on $\tau, A_{\|}, A_{\perp}$

conclusion

If no other nuclear spins were present, one could choose any resonance order (k) to perform the two-qubit gate. In practice however, as k increases, the resonance of the isolated nuclear spin separates from the rest of the bath resulting in a drastic increase of the two-qubit gate fidelity

Estimating the optimal isotopic fraction

High-fidelity qubit control and extended coherences