Analytical approach to swift nonleaky entangling gates in superconducting qubits

TL;DR

This paper presents an analytical method for designing fast, high-fidelity entangling gates in superconducting qubits by intentionally involving harmful transitions, addressing spectral crowding challenges.

Contribution

It introduces a novel analytical pulse design approach that leverages harmful transitions rather than avoiding them, enabling rapid and precise entangling gates.

Findings

Achieved >99% fidelity in 40 ns gates

Successfully implemented CNOT and Z gates in circuit QED

Addresses spectral crowding in multi-qubit systems

Abstract

We develop schemes for designing pulses that implement fast and precise entangling quantum gates in superconducting qubit systems despite the presence of nearby harmful transitions. Our approach is based on purposely involving the nearest harmful transition in the quantum evolution instead of trying to avoid it. Using analytical tools, we design simple microwave control fields that implement maximally entangling gates with fidelities exceeding 99% in times as low as 40 ns. We demonstrate our approach in a two-qubit circuit QED system by designing the two most important quantum entangling gates: a conditional-NOT gate and a conditional-Z gate. Our results constitute an important step toward overcoming the problem of spectral crowding, one of the primary challenges in controlling multi-qubit systems.