Low Overhead Quantum Bus with Coupling beyond the Nearest Neighbor via Mediated Effective Capacitance

TL;DR

This paper proposes a scalable quantum bus architecture using auxiliary transmons to enable tunable, long-range coupling between logical qubits, facilitating multi-qubit entangling gates with low overhead.

Contribution

It introduces a mediated interaction scheme with auxiliary transmons to achieve effective capacitance beyond nearest neighbors in a quantum bus.

Findings

Enables tunable coupling between non-neighboring qubits.

Supports multi-qubit entangling gates.

Reduces control complexity and frequency crowding issues.

Abstract

The design of easy to operate high-fidelity two qubit gates remains an area of ongoing research. Many of the common schemes require dedicated controls lines, while others are vulnerable to issues of frequency crowding. Here, we propose a scheme for coupling a chain of transmons acting as logical qubits via a quantum bus of auxiliary qubits. The auxiliary array is made of floating transmons, and through the use of mediated interactions we generate effective capacitance between them beyond the nearest neighbor. Logical qubits are not directly coupled to each other, but they can be coupled by bringing them closer in frequency to the far-detuned auxiliary arrays. This allows for tunable coupling between non-neighboring logical qubits, and for the application of entangling gates to three or more qubits at once.