# Randomized benchmarking of barrier versus tilt control of a singlet-triplet qubit

## TL;DR

This study uses randomized benchmarking simulations to compare barrier and tilt control in singlet-triplet qubits, revealing that barrier control's advantages depend on noise levels and can be enhanced with optimized composite pulses.

## Contribution

It demonstrates that barrier control can significantly improve qubit coherence and gate fidelity when combined with optimized composite pulses, especially in low nuclear spin noise environments.

## Key findings

- Barrier control improves coherence time in Si qubits by over two orders of magnitude.
- In GaAs, barrier and tilt control show similar coherence times under typical noise.
- Optimized composite pulses make barrier control the superior method for high-fidelity gates.

## Abstract

Decoherence due to charge noise is one of the central challenges in using spin qubits in semiconductor quantum dots as a platform for quantum information processing. Recently, it has been experimentally demonstrated in both Si and GaAs singlet-triplet qubits that the effects of charge noise can be suppressed if qubit operations are implemented using symmetric barrier control instead of the standard tilt control. Here, we investigate the key issue of whether the benefits of barrier control persist over the entire set of single-qubit gates by performing randomized benchmarking simulations. We find the surprising result that the improvement afforded by barrier control depends sensitively on the amount of spin noise: for the minimal nuclear spin noise levels present in Si, the coherence time improves by more than two orders of magnitude whereas in GaAs, by contrast the coherence time is essentially the same for barrier and tilt control. However, we establish that barrier control becomes beneficial if qubit operations are performed using a new family of composite pulses that reduce gate times by up to 90%. With these optimized pulses, barrier control is the best way to achieve high-fidelity quantum gates in singlet-triplet qubits.