Enhanced sensitivity via non-Hermitian topology

Creators: Parto, Midya^{1, 2, 3}; Leefmans, Christian¹; Williams, James¹; Gray, Robert M.¹; Marandi, Alireza¹

1. California Institute of Technology
2. NTT Research
3. University of Central Florida

Abstract

Sensors are indispensable tools of modern life that are ubiquitously used in diverse settings ranging from smartphones and autonomous vehicles to the healthcare industry and space technology. By interfacing multiple sensors that collectively interact with the signal to be measured, one can go beyond the signal-to-noise ratios (SNR) attainable by the individual constituting elements. Such techniques have also been implemented in the quantum regime, where a linear increase in the SNR has been achieved via using entangled states. Along similar lines, coupled non-Hermitian systems have provided yet additional degrees of freedom to obtain better sensors via higher-order exceptional points. Quite recently, a new class of non-Hermitian systems, known as non-Hermitian topological sensors (NTOS) has been theoretically proposed. Remarkably, the synergistic interplay between non-Hermiticity and topology is expected to bestow such sensors with an enhanced sensitivity that grows exponentially with the size of the sensor network. Here, we experimentally demonstrate NTOS using a network of photonic time-multiplexed resonators in the synthetic dimension represented by optical pulses. By judiciously programming the delay lines in such a network, we realize the archetypal Hatano-Nelson model for our non-Hermitian topological sensing scheme. Our experimentally measured sensitivities for different lattice sizes confirm the characteristic exponential enhancement of NTOS. We show that this peculiar response arises due to the combined synergy between non-Hermiticity and topology, something that is absent in Hermitian topological lattices. Our demonstration of NTOS paves the way for realizing sensors with unprecedented sensitivities.

Copyright and License

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Acknowledgement

The authors acknowledge support from ARO Grant W911NF-23-1-0048, NSF Grants No. 1846273 and 1918549 and the Center for Sensing to Intelligence at Caltech. The authors wish to thank NTT Research for their financial and technical support.

Contributions

These authors contributed equally: Midya Parto, Christian Leefmans.

All authors contributed to the writing of this manuscript.

Data Availability

The data used to generate the plots and results in this paper is available from the corresponding author upon reasonable request.

Conflict of Interest

A.M. has financial interest in PINC Technologies Inc., which is developing photonic integrated nonlinear circuits. The remaining authors declare no competing interests.

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