Minimising spin relaxation in donor atom qubits in silicon

Donor electron spin qubits hosted within nanoscale devices have demonstrated seconds-long relaxation times [1-4] at magnetic fields suitable for the operation of spin qubits in silicon of B = 1.5 T. The relaxation rates of these qubits have been shown at milliKelvin temperatures to be mediated by spin-orbit coupling with a B⁵ dependency on magnetic field for B > 3T with a transition to a B³ dependency at magnetic fields below (B ≤ 3T) particularly in multi-donor quantum dot qubits [4]. We identify the relaxation mechanisms that give rise to this saturation at low field and show how, by atomically engineering the device we can minimise this effect extending T₁ to ∼200 seconds at B = 1.5 T.

[1] A. Morello et al., Single-shot readout of an electron spin in silicon, Nature 467, 687 (2010).

[2] T. F. Watson et al., High-fidelity rapid initialization and read-out of an electron spin via the single donor D- charge state, Physical Review Letters 115, 166806 (2015).

[3] B. Weber et al., Spin–orbit coupling in silicon for electrons bound to donors, npj Quantum Information 4, 61 (2018).

[4] T. F. Watson et al., Atomically engineered electron spin lifetimes of 30 s in silicon, Science Advances 3, e1602811 (2017).