Photonic sensor successfully breaks the quantum limit
Quantum technology promises to revolutionize today's sensors ,dramatically improving their performance through more precise, faster, and more reliable measurements of physical quantities. However, most quantum sensing schemes rely on special entangled or squeezed states of light or matter that are difficult to generate and detect, which is a major obstacle to harnessing the capabilities of quantum sensors and deploying them in real-world scenarios.
A joint team from the Universities of Bristol, Bath and Warwick has found a way to operate a large-scale manufacturable photonic sensor at the quantum limit, and demonstrated that without the need for complex optical quantum states and detection schemes , enabling high-precision measurements of important physical properties.
On June 6, the related research results were published in Physical Review Letters under the title "Advantages of Coherent States in Ring Resonators Over Any Quantum Probe One-Way Absorption Estimation Strategy"[1].
Nanofabricated photonic chips with microring resonators fabricated in a commercial foundry.
The key to this breakthrough was the use of ring resonators -- tiny racetrack structures that guide light in the loop and maximize its interaction with the sample under study. Importantly, ring resonators can be fabricated at scale using the same process as chips in computers and smartphones.
All-pass ring resonator with self-coupling coefficient r, round-trip phase ϕ. The research team attempted to estimate the absorption coefficient α A or the refractive index n A of the analyte evanescently coupled to the ring resonator .
Quantum states of light have been shown to improve the accuracy of absorption estimates compared to classical strategies. By exploiting interference and resonance-enhancing effects, they show that coherent state probes in all-pass ring resonators can outperform any quantum-probe single-pass (SP) strategy even when normalized by the average input photon number.
Δα normalized by the mean input photon number (blue) of the all-pass ring resonator probed by the coherent state , the quantum limit of the single-pass (SP) strategy can be probed by the Fock state (purple) and the coherent state Needle (green) implementation. For both SP strategies, the analyte length was continuously optimized with changes in αA . For the target α A =10 cm −1 , the all-pass ring resonator is critically coupled. Optimizing the self-coupling coefficient r further improves its performance (blue dashed line).
Using the technique to sense changes in absorption or refractive index, the team says, could be used to identify and characterize a wide variety of materials and biochemical samples, with applications ranging from monitoring greenhouse gases to cancer detection.
"We are one step closer to an integrated photonic sensor that works at the detection limit imposed by quantum mechanics," said Alex Belsley, PhD student at the University of Bristol's Quantum Engineering Technology Laboratory (QET) and lead author of the work.
Associate Professor Jonathan Matthews, co-director of the QET laboratory and co-author of the study, said: "We are very excited about the opportunities presented by this result. We now know how to use large-scale manufacturable processes to design chip-scale working at the quantum limit. Photon sensors."
This research was supported by funding from the UK National Quantum Technology Programme, QUANTIC UK Centre for Quantum Technologies for Quantum Enhanced Imaging, EPSRC Quantum Engineering Doctoral Training Centre and the European Research Council [2].
About the Quantum Engineering Technology Laboratory
QET Labs was established in 2015 with the mission to bring quantum scientific discoveries out of the lab for the benefit of society. New avenues including quantum computing hardware, quantum communications, enhanced sensing and imaging, and new platforms to study fundamental quantum physics. The QET Lab brings together projects worth over £28 million and is made up of over 100 academics, staff and students from the School of Physics and Electrical and Electronic Engineering.
Reference link:
[1] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.230501
[2] https://www.bristol.ac.uk/news/2022/june/photonic-sensors.html
