Proposed Five-Electron Charge Quadrupole Qubit

TL;DR

This paper introduces the p orbital (pO) charge qubit in a five-electron silicon quantum dot, leveraging quadrupole coupling to reduce decoherence and improve qubit performance through all-electrical control and quadrupole interactions.

Contribution

It proposes a novel five-electron silicon quantum dot qubit based on quadrupole moments, demonstrating enhanced quality factor, control, and two-qubit gate implementation.

Findings

Estimated $T_2^* \sim 80$ ns for the pO qubit

Order of magnitude improvement in quality factor over existing spin qubits

Feasible two-qubit gates via quadrupole-quadrupole interactions

Abstract

A charge qubit couples to environmental electric field fluctuations through its dipole moment, resulting in fast decoherence. We propose the p orbital (pO) qubit, formed by the single electron, p-like valence states of a five-electron Si quantum dot, which couples to charge noise through the quadrupole moment. We demonstrate that the pO qubit offers distinct advantages in quality factor, gate speed, readout and size. We use a phenomenological, dipole two-level-fluctuator charge noise model to estimate a $T_2^* \sim 80$ ns. In conjunction with Rabi frequencies of order 10 GHz, an order of magnitude improvement in qubit quality factor is expected relative to state-of-the-art semiconductor spin qubits. The pO qubit features all-electrical control via modulating the dot's eccentricity. We also show how to perform two-qubit gates via the $1/r^5$ quadrupole-quadrupole interaction. We find a universal gate set using gradient ascent based control pulse optimization, subject to 10 GHz maximum allowable bandwidth and 1 ns pulse times.