Four-state discrimination for a pair of spin qubits via gate reflectometry

TL;DR

This paper proposes a gate reflectometry method for discriminating all four spin qubit states in a double quantum dot, enhancing readout fidelity for scalable quantum computing.

Contribution

It introduces a quantitative, single-measurement technique for four-state discrimination using gate reflectometry, tailored for silicon quantum dots with noise and relaxation considerations.

Findings

Maximized contrast between quantum capacitances of basis states.

Analyzed effects of amplifier noise and phonon relaxation on fidelity.

Demonstrated potential to reduce readout overhead in spin qubits.

Abstract

Single-electron spin qubits defined in quantum dots are used as building blocks of a semiconductor-based quantum computer. Readout in a scaled-up version of such a quantum computer is expected to rely on the Pauli Spin Blockade (PSB) mechanism. A desired functionality of PSB readout is that it reveals two bits of information on the two spin qubits that are involved in the process, such that the four computational basis states can be discriminated. In this work, we propose and quantitatively analyze an experimental procedure, based on gate reflectometry, which enables this four-state discrimination in a single measurement. We provide an intuitive recipe to maximize the contrast between the quantum capacitances of the four basis states. Focusing on silicon double quantum dots equipped with a micromagnet, we quantify how amplifier noise and phonon-mediated relaxation influence readout fidelity. Our results highlight a realistic opportunity to mitigate the overhead of readout ancilla qubits in a spin-based quantum computer.