External field control of donor electron exchange at theSi∕SiO2interface

Abstract

We analyze several important issues for the single-and two-qubit operations in Si quantum computer architectures involving P donors close to a SiO2 interface. For a single donor, we investigate the donor-bound electron manipulation (i.e. 1-qubit operation) between the donor and the interface by electric and magnetic fields. We establish conditions to keep a donor-bound state at the interface in the absence of local surface gates, and estimate the maximum planar density of donors allowed to avoid the formation of a 2-dimensional electron gas at the interface. We also calculate the times involved in single electron shuttling between the donor and the interface. For a donor pair, we find that under certain conditions the exchange coupling (i.e. 2-qubit operation) between the respective electron pair at the interface may be of the same order of magnitude as the coupling in GaAs-based two-electron double quantum dots where coherent spin manipulation and control has been recently demonstrated (for example for donors ∼ 10 nm below the interface and ∼ 40 nm apart, J ∼ 10 −4 meV), opening the perspective for similar experiments to be performed in Si.

A computational workflow for designing silicon donor qubits

“…These process errors complicate control of the resulting qubit. Moreover, they are in addition to the decoherence caused by external noise, defects, spectral diffusion, and charge buildup at the electrode interfaces, which undermines the desired dynamics [29].…”

Two-dimensional electron states bound to an off-plane donor in a magnetic field

“…In general, a finite thickness of the confinement potential in a quasi-2D system can reduce the binding energies of the localized states [8]. The charge images of the impurity and the electron and the screening of the metallic gate leads to a lowering of the energy levels [2,9].…”

“…Recent progress in dopant engineering and coherent control of dopant states, together with the amazing advances in Si technology, have accelerated the realization of devices based on the quantum functionality of single dopants [2,3]. Basic elements such as P and As are promising candidates, as dopants, in these nanometer-scale quantum electronic devices.…”

“…An electric gate or an external magnetic field can be used to control and manipulate the electronic states to realize the operation of the devices. The ground state of a donor localized near a semiconductor/insulator/metal interface was recently investigated by using the finite element technique [9,10], the variational approach [2,9] and the quantum Monte Carlo simulation [11]. The effects of the gate potential, the screening of the metallic gate, the finite thickness of the insulator layer between the semiconductor and the gate, as well as the image charge on the impurity potential and the donor states, were investigated [9,10].…”

“…In [2], Calderon et al studied the ground state energy of a donor localized in Si near an interface with a thick insulating layer in applied electric and magnetic fields perpendicular to the interface, taking into account the charge images of the impurity and the electron. They showed the existence of a well-defined interface state where the electron remains bound to its donor and localized in the semiconductor/insulator interface.…”