Tunable coupler to fully decouple and maximally localize superconducting qubits

TL;DR

This paper introduces a tunable coupler design for superconducting qubits that fully suppresses crosstalk and localizes qubit states, enabling high-fidelity gates in large-scale quantum processors.

Contribution

The authors propose a novel coupler model that achieves complete decoupling of dispersively detuned Transmon qubits while maintaining maximal localization, improving scalability and gate fidelity.

Findings

Simulated 40ns CZ-gate with process infidelity below coherence limits.

Full qubit isolation during gate operations in large qubit grids.

Suppression of ZZ-crosstalk while preserving qubit localization.

Abstract

Enhancing the capabilities of superconducting quantum hardware, requires higher gate fidelities and lower crosstalk, particularly in larger scale devices, in which qubits are coupled to multiple neighbors. Progress towards both of these objectives would highly benefit from the ability to fully control all interactions between pairs of qubits. Here we propose a new coupler model that allows to fully decouple dispersively detuned Transmon qubits from each other, i.e. ZZ-crosstalk is completely suppressed while maintaining a maximal localization of the qubits' computational basis states. We further reason that, for a dispersively detuned Transmon system, this can only be the case if the anharmonicity of the coupler is positive at the idling point. A simulation of a 40ns CZ-gate for a lumped element model suggests that achievable process infidelity can be pushed below the limit imposed by state-of-the-art coherence times of Transmon qubits. On the other hand, idle gates between qubits are no longer limited by parasitic interactions. We show that our scheme can be applied to large integrated qubit grids, where it allows to fully isolate a pair of qubits, that undergoes a gate operation, from the rest of the chip while simultaneously pushing the fidelity of gates to the limit set by the coherence time of the individual qubits.