Double-Transmon Coupler: Fast Two-Qubit Gate with No Residual Coupling for Highly Detuned Superconducting Qubits

TL;DR

This paper introduces a double-transmon coupler that enables fast, high-fidelity two-qubit gates with no residual coupling during idle times in superconducting qubits, addressing key challenges in quantum computing.

Contribution

The paper proposes a novel double-transmon coupler design that achieves tunable coupling with no residual interaction for highly detuned superconducting qubits.

Findings

Enables fast two-qubit gates with high fidelity

Eliminates residual coupling during idle periods

Suitable for highly detuned fixed-frequency transmons

Abstract

Although two-qubit entangling gates are necessary for universal quantum computing, they are notoriously difficult to implement with high fidelity. Recently, tunable couplers have become a key component for realizing high-fidelity two-qubit gates in superconducting quantum computers. However, it is still difficult to achieve tunable coupling free of unwanted residual coupling for highly detuned qubits, which are desirable for mitigating qubit-frequency crowding or errors due to crosstalk between qubits. We thus propose a design for this kind of tunable coupler, which we call a double-transmon coupler, because this is composed of two transmon qubits coupled through a common loop with an additional Josephson junction. Controlling the magnetic flux in the loop, we can achieve not only fast high-fidelity two-qubit gates, but also no residual coupling during idle time, where computational qubits are highly detuned fixed-frequency transmons. The proposed coupler is expected to offer an alternative approach to higher-performance superconducting quantum computers.