Sign- and magnitude-tunable coupler for superconducting flux qubits

TL;DR

This paper demonstrates an experimentally tunable coupling element for superconducting flux qubits, allowing in situ control of the coupling strength and sign, which is crucial for quantum computing applications.

Contribution

The work introduces a coupling element with tunable sign and magnitude for flux qubits, verified through ground state mapping and direct qubit readout.

Findings

Coupling strength J can be tuned from antiferromagnetic to ferromagnetic.

The coupling sign and magnitude are controllable in situ.

Ground state mapping confirms tunability of the coupling.

Abstract

We experimentally confirm the functionality of a coupling element for flux-based superconducting qubits, with a coupling strength $J$ whose sign and magnitude can be tuned {\it in situ}. To measure the effective $J$, the groundstate of a coupled two-qubit system has been mapped as a function of the local magnetic fields applied to each qubit. The state of the system is determined by directly reading out the individual qubits while tunneling is suppressed. These measurements demonstrate that $J$ can be tuned from antiferromagnetic through zero to ferromagnetic.