Quantum Network Demonstrates Entanglement-Assisted Non-local Optical Interferometry for Improved Low-Light Measurements

The challenge of detecting faint light signals, crucial for applications like astronomical observation and secure communication, often limits the performance of optical instruments. Researchers, including P. -J. Stas, Y. -C. Wei, and M. Sirotin from Harvard University, alongside colleagues, now demonstrate a significant step towards overcoming this limitation by harnessing the power of quantum entanglement. They successfully perform a remote measurement of weak light signals using entangled memories within a quantum network, connecting two points via a fibre optic link extending 1. 55km. This innovative approach, which effectively hides information about the path of individual photons, promises to enhance the sensitivity of imaging technologies and pave the way for a new generation of quantum-enhanced optical instruments.

Entanglement Beats Classical Noise in Optics

The sensitivity of optical measurements at low light levels is fundamentally limited by classical noise sources. Researchers are investigating techniques to overcome these limitations and achieve enhanced sensitivity in optical measurements by employing a heralded entanglement-based protocol, utilising time-bin encoding and post-selection on a heralded entangled photon pair. This method effectively suppresses classical noise by exploiting quantum correlations, allowing for the detection of signals below the standard quantum limit. The team demonstrates a 3. 2 dB improvement in signal-to-noise ratio compared to conventional homodyne detection, establishing a pathway for developing advanced quantum sensors and imaging systems with unprecedented sensitivity and precision. Experimental verification confirms the suppression of classical noise and enhancement of signal detection capabilities, offering a novel approach to mitigating noise in optical measurements by leveraging heralded entanglement.

Entangled Photons Enhance Phase Sensing Accuracy

This research focuses on a protocol for non-local phase sensing using entangled photons and silicon-vacancy (SiV) centers in diamond, aiming to achieve a higher signal-to-noise ratio compared to traditional local measurement methods. The protocol measures a phase shift on one photon by correlating it with its entangled partner, utilising a telescope array to prepare a specific entangled state. A crucial component, the Single-Mode Single-Photon Gate, conditionally reflects or transmits photons based on the SiV’s state. Current limitations include the efficiency of this gate, imperfect Bell state fidelity, and photonic loss. Replacing the current amplitude-based Single-Mode Single-Photon Gate with a phase-based version would eliminate photon loss, double heralding efficiency, and increase the signal-to-noise ratio. Improving Bell state fidelity and reducing photonic loss would further enhance performance.

Kilometer-Scale Interferometry with Quantum Memories

This research demonstrates a new approach to non-local optical measurements, achieving interferometry across a 1. 55km fiber link, five times longer than the current state-of-the-art. Scientists successfully implemented a quantum memory-assisted interferometer, utilising entangled memories within silicon-vacancy (SiV) centers in diamond nanophotonic cavities to perform differential phase measurements of weak light between two spatially separated stations. This advancement combines event-ready remote entanglement, photon mode erasure, and non-local, non-destructive photon heralding to enhance sensitivity and overcome limitations of traditional interferometry, where signal loss exponentially increases with distance. The system utilises SiV centers functioning as two-qubit registers, enabling efficient spin-photon operations and long-lived quantum memories, resulting in a significant improvement in signal-to-noise ratio compared to conventional methods.

Remote Entanglement Boosts Long-Distance Sensitivity

This research demonstrates a new approach to enhancing the sensitivity of optical measurements over long distances, utilising remote entanglement between quantum bits. By combining entangled memories with a technique to conceal the path of incoming light and non-destructive photon heralding, the team successfully performed a proof-of-concept measurement of weak light signals between two stations linked by a 1. 55km fibre optic cable. This successful demonstration opens avenues for future advancements in quantum networking and distributed sensing, with potential for significant improvements in applications such as long baseline telescope arrays and other enhanced imaging technologies. Future work will likely focus on simplifying the system, improving the robustness of entanglement, and exploring the scalability of this technique to larger networks and more complex measurements.