Tunability of qubit Coulomb interaction: Numerical analysis of top gate depletion in two-dimensional electron systems

TL;DR

This study numerically analyzes how the Coulomb interaction between quantum dots in 2DEG systems can be electrically tuned using top gates, revealing limited but significant tunability due to screening effects.

Contribution

It provides a detailed numerical analysis of Coulomb interaction tunability in 2DEG-based quantum dots, highlighting the limitations and potential of electrical control.

Findings

Coulomb interaction is generally weak (~1 μeV) due to screening.

Complete suppression of qubit interaction is not feasible.

Approximately 50% tunability of Coulomb interaction is achievable.

Abstract

We investigate the tunability of electrostatic coupling between solid state quantum dots as building blocks for quantum bits. Specifically, our analysis is based upon two-dimensional electron systems (2DEG) and depletion by top gates. We are interested in whether the Coulomb interaction between qubits can be tuned by electrical means using screening effects. The systems under investigation are analyzed numerically solving the Poisson equation in 3D via relaxation techniques with optimized algorithms for an extended set of boundary conditions. These include an open outer boundary, simulation of 2DEG systems and dielectric boundaries like the surface of a physical sample. The results show that for currently lithographically available feature sizes, the Coulomb interaction between the quantum bits is weak in general due to efficient screening in the planar geometry of 2DEG and top gates. The evaluated values are on the order of 1 $\mu$eV. Moreover, while it is not possible to turn off the qubit interaction completely, an effective tunability on the order of 50% is clearly realizable while maintaining an intact quantum bit structure.