Readout of singlet-triplet spin qubit in donor-based devices in silicon*

Singlet-triplet qubits have been investigated in gate-defined quantum dot systems where micromagnets are used to generate large magnetic field gradients for high-fidelity electrically-controlled qubit operations. However, the large magnetic field gradients increase the triplet relaxation making readout difficult. Here, we theoretically examine shelving and latching singlet-triplet readout techniques for donor-based devices in silicon where the large phosphorus hyperfine interaction leads to large effective magnetic field gradients. Using numerical simulations, we analyse how devices can be engineered for maximum readout visibility and show that singlet-triplet qubits based on phosphorus donors are a promising route for future electrically controlled qubits in silicon without the need of micromagnet.