Electro-optic conversion of itinerant Fock states

TL;DR

This paper demonstrates the on-demand generation and optical upconversion of non-classical microwave photon states from superconducting qubits, advancing quantum communication and distributed quantum computing.

Contribution

It introduces a method for microwave-to-optical conversion of non-Gaussian states with low added noise, enabling integration of superconducting qubits into quantum networks.

Findings

Achieved heralded generation of itinerant single microwave photons.

Demonstrated low-noise optical upconversion with added noise below 0.012 quanta.

Counted converted telecom photons with a signal-to-noise ratio up to 5.1.

Abstract

Superconducting qubits are a leading candidate for utility-scale quantum computing due to their fast gate speeds and steadily decreasing error rates. The requirement for millikelvin operating temperatures, however, creates a significant scaling bottleneck. Modular architectures using optical fiber links could bridge separate cryogenic nodes, but superconducting circuits do not have coherent optical transitions and microwave-to-optical conversion has not been shown for any non-classical photon state. In this work, we demonstrate the on-demand generation and tomographic reconstruction of itinerant single microwave photons at 8.9 GHz from a superconducting qubit. We upconvert this non-Gaussian state with a transducer added noise below 0.012 quanta and count the converted telecom photons at 193.4 THz with a signal-to-noise ratio of up to 5.1$\pm$1.1. We characterize the trade-offs between throughput and noise, and establish a viable path toward heralded entanglement distribution and gate teleportation. Looking ahead, these results empower existing superconducting devices to take a key role in distributed quantum technologies and heterogeneous quantum systems.