Single-shot readout and relaxation of singlet/triplet states in exchange-coupled $^{31}$P electron spins in silicon

Understand

We present the experimental observation of a large exchange coupling $J \approx 300$ $\mu$eV between two $^{31}$P electron spin qubits in silicon.

• The singlet and triplet states of the coupled spins are monitored in real time by a Single-Electron Transistor, which detects ionization from tunnel-rate-dependent processes in the coupled spin system, yielding single-shot readout fidelities above 95%.
• The triplet to singlet relaxation time $T_1 \approx 4$ ms at zero magnetic field agrees with the theoretical prediction for $J$-coupled $^{31}$P dimers in silicon.
• The time evolution of the 2-electron state populations gives further insight into the valley-orbit eigenstates of the donor dimer, valley selection rules and relaxation rates, and the role of hyperfine interactions.