Electronic Control and Readout of Qubit States in Solid State Quantum Computing Systems

TL;DR

This paper proposes using an $n^+/i/n^+$ junction as an effective system for controlling and reading out qubit states in solid-state quantum computing, leveraging a self-induced barrier and precise dopant placement.

Contribution

It introduces a novel $n^+/i/n^+$ junction design for qubit control and readout, demonstrating its ability to manipulate and measure impurity-based qubit states in silicon.

Findings

Self-induced barrier exists over a wide dopant concentration range.

Barrier height can be tuned via doping levels.

Qubit states are well separated from electrode continuum.

Abstract

We demonstrate that an $n^+/i/n^+$ junction is the most suitable candidate for electronic control and readout of qubit states in quantum computing systems based on shallow impurities. The signature of this system is that the $n^+-$regions serve as metallic electrodes separated form the $i-$region by a self-induced barrier (internal workfunction). The $n^+/i/n^+$ system mimics the properties of a metal-vacuum-metal junction with the qubit (impurity atom) placed in a ``vacuum'' $i$-region between two ``metallic'' $n^+$ electrodes. We will show that the self-induced barrier exists in a sufficiently wide range of the concentration of dopants in the $n^+$-semiconductor (e.g. up to $10^{21}$ cm$^{-3}$ for Si) and its height can be controlled by tuning the doping level. A shallow donor placed in a vacuum $i$-region will be populated with one electron in equilibrium. In the case of Li donor in Si the $n^+$-electrodes will be used for a precision placement of the Li atom during the growth process; for voltage control and manipulation of the qubit states; and for a qubit readout by means of the optically stimulated resonant tunnelling. Another important feature of our system is that the qubit states (first two lowest energy levels of Li in Si) are separated by an energy gap from a continuum of the many-body states of the controlling electrodes.