Deterministic Quantum Communication Between Fixed-Frequency Superconducting Qubits via Broadband Resonators

TL;DR

This paper demonstrates deterministic quantum communication between fixed-frequency superconducting qubits using broadband resonators, enabling scalable quantum networks without complex control lines.

Contribution

It introduces a broadband transfer resonator design and a frequency-tunable photon-generation technique for scalable, fixed-frequency quantum communication.

Findings

Achieved quantum state transfer fidelity of ~79%.

Generated Bell states with ~73% fidelity.

Enabled communication over a 30-MHz photon frequency range.

Abstract

Quantum communication between remote chips is essential for realizing large-scale superconducting quantum computers. For such communication, itinerant microwave photons propagating through transmission lines offer a promising approach. However, demonstrations to date have relied on frequency-tunable circuit elements to compensate for fabrication-related parameter variations between sender and receiver devices, introducing control complexity and limiting scalability. In this work, we demonstrate deterministic quantum state transfer and remote entanglement generation between fixed-frequency superconducting qubits on separate chips. To compensate for the sender-receiver mismatch, we employ a frequency-tunable photon-generation technique which enables us to adjust the photon frequency without modifying circuit parameters. To enhance the frequency tunability, we implement broadband transfer resonators composed of two coupled coplanar-waveguide resonators, achieving a bandwidth of more than 100 MHz. This broadband design enables successful quantum communication across a 30-MHz range of photon frequencies between the remote qubits. Quantum process tomography reveals state transfer fidelities of around 79% and Bell-state fidelities of around 73% across the full frequency range. Our approach avoids the complexity of the control lines and noise channels, providing a flexible pathway toward scalable quantum networks.