A quantum-bit encoding converter

TL;DR

This paper demonstrates a novel, high-fidelity quantum-bit encoding converter that seamlessly translates quantum information between discrete- and continuous-variable formats, crucial for scalable quantum networks.

Contribution

It introduces the first postselection-free method for converting quantum information between main quantum-bit encodings with high fidelity.

Findings

Successfully converts single-photon qubits to cat-state qubits

Fidelities exceed the classical limit, confirming quantum coherence preservation

Enables interconnected quantum devices with enhanced versatility

Abstract

From telecommunication to computing architectures, the realm of classical information hinges on converter technology to enable the exchange of data between digital and analog formats, a process now routinely performed across a variety of electronic devices. A similar exigency exists as well in quantum information technology where different frameworks are being developed for quantum computing, communication, and sensing. Thus, efficient quantum interconnects are a major need to bring these parallel approaches together and scale up quantum information systems. So far, however, the conversion between different optical quantum-bit encodings has remained challenging due to the difficulty of preserving fragile quantum superpositions and the demanding requirements for postselection-free implementations. Here we demonstrate such a conversion of quantum information between the two main paradigms, namely discrete- and continuous-variable qubits. We certify the protocol on a complete set of single-photon qubits, successfully converting them to cat-state qubits with fidelities exceeding the classical limit. Our result demonstrates an essential tool for enabling interconnected quantum devices and architectures with enhanced versatility and scalability.