Quantum Entanglement of Remote Qubits Boosts Fidelity with Time-Bin Encoding.

Researchers demonstrate improved remote entanglement of superconducting qubits using microwave transduction and multi-time-bin encoding, achieving fidelity increases from 0.75 to 0.89 in ideal systems and 0.66 to 0.89 even with noise. This protocol reduces thermal interference without purification, enabling scalable quantum systems.

The pursuit of robust quantum communication necessitates efficient entanglement distribution over significant distances, a challenge currently limited by signal degradation and loss. Researchers are now exploring novel methods to connect disparate quantum systems, moving beyond traditional photonic approaches. A team at Fermi National Accelerator Laboratory, comprising Jing Wu, Changqing Wang, Andrew Cameron, and Silvia Zorzetti, details a protocol for entangling remote superconducting qubits, utilising microwave transduction and multi-time-bin encoding. Their work, entitled “Entangling remote superconducting qubits via transducer-generated multi-time-bin states”, demonstrates improved fidelity in both ideal transduction systems and those subject to noise, offering a potentially scalable architecture for future heterogeneous quantum networks. Multi-time-bin encoding refers to a method of representing quantum information across multiple distinct time intervals, enhancing the robustness of the signal against decoherence. Transduction, in this context, involves converting quantum information between different physical systems, such as superconducting qubits and microwave photons.

Recent advances demonstrate long-distance quantum entanglement utilising nitrogen-vacancy (NV) centres, atoms, and quantum dots, often employing time-bin encoding of photons. Researchers now propose a method to entangle remote superconducting qubits via microwave transduction, leveraging multi-time-bin states to enhance performance. Superconducting qubits are a leading platform for building quantum computers, and microwave transduction is the process of converting quantum information between different forms, in this case, between qubits and microwave signals.

This work demonstrates a viable pathway towards scalable, heterogeneous quantum systems by enhancing entanglement between remote superconducting qubits. By distributing quantum information across multiple discrete time intervals, the protocol increases the robustness of the entangled state against decoherence – the loss of quantum information – and transmission losses. This circumvents the need for complex purification procedures, simplifying experimental setups and reducing overhead. The successful implementation facilitates the interconnection of diverse qubit technologies, paving the way for more powerful and versatile quantum networks.

The protocol actively mitigates the effects of thermal noise, a pervasive challenge in superconducting qubit systems. It achieves this through the inherent properties of the multi-time-bin encoding scheme, which distributes quantum information in a manner less susceptible to thermal fluctuations. This resilience to thermal noise represents a crucial step towards building stable and reliable quantum networks.

Detailed fidelity calculations provide a robust foundation for optimising system performance and realising the potential of multi-time-bin entanglement in future quantum networks. Researchers introduce a normalisation constant, (K_0), which accounts for the behaviour of the system with varying numbers of time bins, highlighting the subtle differences in performance depending on whether an even or odd number of bins are employed. The calculations rigorously quantify how fidelity scales with the number of time bins used and the efficiency of the transduction process.

Researchers demonstrate a measurable improvement in fidelity, increasing performance from 0.75 to a value exceeding 0.89 in transduction systems and from 0.66 to 0.89 within noisy channels. This indicates a significant advancement in the practical implementation of quantum communication protocols.

By facilitating entanglement between disparate qubit technologies via microwave transduction, the method enables the integration of diverse quantum processors into a unified network. This integration is crucial for leveraging the strengths of different qubit platforms and building more complex and powerful quantum systems.