A robust operating point for capacitively coupled singlet-triplet qubits

TL;DR

This paper identifies a special operating point in capacitively coupled singlet-triplet qubits that minimizes charge noise sensitivity while enabling high-fidelity entangling gates, with simulations showing over 99% fidelity.

Contribution

It introduces an interacting sweet spot for singlet-triplet qubits that enhances two-qubit gate fidelity by reducing charge noise effects.

Findings

The sweet spot exists only with interqubit interactions.

Working at this point yields maximally entangling gates.

Simulations show gate fidelities above 99% under realistic noise.

Abstract

Singlet-triplet qubits in lateral quantum dots in semiconductor heterostructures exhibit high-fidelity single-qubit gates via exchange interactions and magnetic field gradients. High-fidelity two-qubit entangling gates are challenging to generate since weak interqubit interactions result in slow gates that accumulate error in the presence of noise. However, the interqubit electrostatic interaction also produces a shift in the local double well detunings, effectively changing the dependence of exchange on the gate voltages. We consider an operating point where the effective exchange is first order insensitive to charge fluctuations while maintaining nonzero interactions. This "sweet spot" exists only in the presence of interactions. We show that working at the interacting sweet spot can directly produce maximally entangling gates and we simulate the gate evolution under realistic 1/f noise. We report theoretical two-qubit gate fidelities above 99% in GaAs and Si systems.