On-demand electrical control of spin qubits

Abstract

Once called a "classically non-describable two-valuedness" by Pauli [1], the electron spin is a natural resource for long-lived quantum information since it is mostly impervious to electric fluctuations and can be replicated in large arrays using silicon quantum dots, which offer high-fidelity control [2][3][4][5]. Paradoxically, one of the most convenient control strategies is the integration of nanoscale magnets to artificially enhance the coupling between spins and electric field [6-8], which in turn hampers the spin's noise immunity [9] and adds architectural complexity [10]. Here we demonstrate a technique that enables a switchable interaction between spins and orbital motion of electrons in silicon quantum dots, without the presence of a micromagnet. The naturally weak effects of the relativistic spin-orbit interaction in silicon are enhanced by more than three orders of magnitude by controlling the energy quantisation of electrons in the nanostructure, enhancing the orbital motion. Fast electrical control is demonstrated in multiple devices and electronic configurations, highlighting the utility of the technique. Using the electrical drive we achieve coherence time T2,Hahn ≈ 50 µs, fast single-qubit gates with T π/2 = 3 ns and gate fidelities of 99% probed by randomised benchmarking. The higher gate speeds and better compatibility with CMOS manufacturing enabled by on-demand electric control improve the prospects for realising scalable silicon quantum processors.

Spin-orbit enhancement in Si/SiGe heterostructures with oscillating Ge concentration

“…With regards to possible applications, the enhanced spin-orbit coupling of the Wiggle Well indicates that EDSR can be used for fast, electrically-driven manipulations of single-spin, Loss-DiVincenzo qubits without the use of micromagnets. Indeed, a fast, spin-orbit driven EDSR capability is one of the main attractive features of hole-spin qubits [17,[43][44][45][46], and has recently also attracted interest in Si electron-spin qubits [47]. This possibility is supported by our calculations in Sec.…”