All-electrical manipulation of silicon spin qubits with tunable spin-valley mixing

Abstract

We show that the mixing between spin and valley degrees of freedom in a silicon quantum bit (qubit) can be controlled by a static electric field acting on the valley splitting ∆. Thanks to spinorbit coupling, the qubit can be continuously switched between a spin mode (where the quantum information is encoded into the spin) and a valley mode (where the the quantum information is encoded into the valley). In the spin mode, the qubit is more robust with respect to inelastic relaxation and decoherence, but is hardly addressable electrically. It can however be brought into the valley mode then back to the spin mode for electrical manipulation. This opens new perspectives for the development of robust and scalable, electrically addressable spin qubits on silicon. We illustrate this with tight-binding simulations on a so-called "corner dot" in a silicon-on-insulator device where the confinement and valley splitting can be independently tailored by a front and a back gate.

Electrical manipulation of semiconductor spin qubits within the g -matrix formalism

“…The back gate therefore controls the position and symmetry of the hole wave function, as it does for electrons. 45 The confinement in corner dots is, however, less pronounced for holes than for electrons 51 due to the different mass anisotropies. We can actually conjecture from Fig.…”

“…Such a qubit may, in principle, be switched between a bias point (e.g., V bg = −0.2 V) where it is strongly coupled to the RF electric field for manipulation and a bias point (V bg = −0.15 V) where it gets largely decoupled, but is as a consequence more immune to charge and gate noise. 45,53 Beyond the dip near V bg = −0.15 V, the Rabi frequency also decreases at large |V bg | when the hole gets localized on the left or right of the channel. This mostly results from a decrease of the dipole matrix elements 1, σ |D 1 |0, σ between the strongly confined ground-and first excited states (as well as from an increase of the corresponding denominator in Eq.…”

Electric-field tuning of the valley splitting in silicon corner dots

“…The single-particle energy levels are computed in the electrostatic potential from the gates (see Refs. 12,16 for details). The surface of the channel is passivated with pseudo-hydrogen atoms, but the effective oxide model of Ref.…”

Electric-field control and noise protection of the flopping-mode spin qubit

“…This expression should be viewed as an approximate interpolation between the limiting cases where relaxation rate γ 1,s or the low-frequency noise are dominating [50]. Increasing the detuning localizes the electron more in a single QD and the flopping-mode EDSR mechanism described above may compete with other EDSR mechanisms that take place in a SQD, via excited orbital or valley states [23,27,[51][52][53][54][55][56]. Also in a DQD structure, if the intervalley interdot tunnel coupling [57][58][59] is strong compared to the valley splittings [59], the effective spin Rabi frequency will be modified.…”