Interface induced spin-orbit interaction in silicon quantum dots and\n prospects for scalability

Abstract

We identify the presence of monoatomic steps at the Si/SiGe or Si/SiO$_2$\ninterface as a dominant source of variations in the dephasing time of Si\nquantum dot (QD) spin qubits. First, using atomistc tight-binding calculations\nwe show that the g-factors and their Stark shifts undergo variations due to\nthese steps. We compare our theoretical predictions with experiments on QDs at\na Si/SiO$_2$ interface, in which we observe significant differences in Stark\nshifts between QDs in two different samples. We also experimentally observe\nvariations in the $g$-factors of one-electron and three-electron spin qubits\nrealized in three neighboring QDs on the same sample, at a level consistent\nwith our calculations. The dephasing times of these qubits also vary, most\nlikely due to their varying sensitivity to charge noise, resulting from\ndifferent interface conditions. More importantly, from our calculations we show\nthat by employing the anisotropic nature of the spin-orbit interaction (SOI) in\na Si QD, we can minimize and control these variations. Ultimately, we predict\nthat the dephasing times of the Si QD spin qubits will be anisotropic and can\nbe improved by at least an order of magnitude, by aligning the external DC\nmagnetic field towards specific crystal directions.\n