Field Demonstration of Distributed Quantum Sensing without Post-Selection

Abstract

Distributed quantum sensing can provide quantum-enhanced sensitivity beyond the shot-noise limit (SNL) for sensing spatially distributed parameters. To date, distributed quantum sensing experiments have mostly been accomplished in laboratory environments without a real space separation for the sensors. In addition, the post-selection is normally assumed to demonstrate the sensitivity advantage over the SNL. Here, we demonstrate distributed quantum sensing with discrete variables in field and show the unconditional violation (without post-selection) of SNL up to 0.916 dB for the field distance of 240 m. The achievement is based on a loophole-free Bell test setup with entangled photon pairs at the averaged heralding efficiency of 73.88%. Moreover, to test quantum sensing in real life, we demonstrate the experiment for long distances (with 10-km fiber), together with the sensing of a completely random parameter. The results represent an important step towards a practical quantum sensing network for widespread applications.

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Plain Language Summary

Distributed quantum sensing networks play a significant role in quantum-enhanced metrology, an active area of research because of its many possible applications ranging from atomic clocks to biological imaging. With a global distribution of sensors, one can determine global properties of the network by precisely estimating all of its parameters. Many studies suggest that by using entanglement among sensors, the sensitivity can surpass the shot-noise limit (SNL), a fundamental sensitivity threshold that cannot be surpassed with classical methods. However, this has not yet been shown in a real-world distributed quantum sensing network. We demonstrate, for the first time, a field test of distributed quantum sensing that unconditionally beats the SNL.

In our experiment, we attempt to measure the phases of two widely separated entangled photons. In the field, we build a distributed quantum sensing apparatus, which includes a source of entangled photon pairs and two sensors—one for each photon in the pair—240 m apart. Our experiment achieves a phase precision of 0.916 dB below the SNL. It also demonstrates a state-of-the-art heralding efficiency—the probability that one photon is detected once the other has been detected—of 73.88%, surpassing the theoretical 59.1% limit that we calculate is needed to violate the SNL. In addition, we simulate the actual sensing working circumstances and show that the unknown phases can be precisely measured for a sensor separation of 10 km.

Our work not only boosts the development of a quantum sensing network with more nodes and larger scale but also transitions the quantum sensing network toward practical applications.