# Coherent coupled qubits for quantum annealing

## TL;DR

This paper explores using flux qubits with smaller persistent currents and longer coherence times for quantum annealing, demonstrating tunable coupling and analyzing coherence factors to improve future quantum annealer design.

## Contribution

It introduces an alternative qubit design with smaller persistent currents and demonstrates tunable coupling, providing insights into enhancing quantum annealer coherence.

## Key findings

- Tunable coupling achieved between flux qubits with small persistent currents.
- Qubit coherence depends on coupler settings and flux noise.
- Insights into design space for next-generation quantum annealers.

## Abstract

Quantum annealing is an optimization technique which potentially leverages quantum tunneling to enhance computational performance. Existing quantum annealers use superconducting flux qubits with short coherence times, limited primarily by the use of large persistent currents $I_\mathrm{p}$. Here, we examine an alternative approach, using qubits with smaller $I_\mathrm{p}$ and longer coherence times. We demonstrate tunable coupling, a basic building block for quantum annealing, between two flux qubits with small ($\sim 50~\mathrm{nA}$) persistent currents. Furthermore, we characterize qubit coherence as a function of coupler setting and investigate the effect of flux noise in the coupler loop on qubit coherence. Our results provide insight into the available design space for next-generation quantum annealers with improved coherence.