An optimal single-electron charge qubit for solid-state double quantum dots

TL;DR

This paper introduces an optimal single-electron charge qubit in a solid-state double quantum dot system, demonstrating its dynamics, initialization, control, and measurement techniques using GPU-accelerated simulations.

Contribution

It proposes a new basis for charge qubits that maximizes overlap with an ideal two-state model and details methods for initialization and control in realistic experimental conditions.

Findings

Optimal qubit basis states are symmetric and antisymmetric combinations of bonding and anti-bonding states.

Single-qubit operations can be performed with at most two pulses using spin-echo type pulsing.

The proposed measurement method involves detecting the electron's probability in each quantum dot.

Abstract

We report on an optimal single-electron charge qubit for a solid-state double quantum dot (DQD) system and analyse its dynamics under a time-dependent linear detuning, using GPU accelerated numerical solutions to the time-dependent Schr\"odinger equation. The optimal qubit is found to have basis states defined as the symmetric and antisymmetric linear combinations of the lowest energy bonding and anti-bonding states of the DQD at zero bias. In contrast to charge qubits defined by the two localised ground states of the uncoupled DQD, this choice of the basis causes the resulting dynamics to have a maximal overlap with an idealised two-state model. Our optimal qubit basis states are not localised to a single quantum dot and, as such, initialising the qubit requires a particular sequence of gate pulses to take the system from an initial fiducial state of the DQD to the logical $0$ or $1$. We determine this sequence using pulses that incorporate the expected experimental finite rise times. We also show how to perform arbitrary single qubit operations on the Bloch sphere using spin-echo type pulsing, allowing us to obtain any qubit state with at most two single pulses. Measurement of the optimal qubits is achieved by determining the probability of finding the electron in one of the dots.