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Physical Review Applied

Loss-Compensated and Enhanced Midinfrared Interaction-Free Sensing with Undetected Photons

Nathan R. Gemmell, Jefferson Flórez, Emma J. Pearce, Olaf Czerwinski, Chris C. Phillips, Rupert F. Oulton, Alex S. Clark

Published May 5, 2023• 15 citations
Publisher

Abstract

Sensing with undetected photons is a fascinating technique that allows imaging at wavelengths outside a particular detector's range---enabling, for example, biological imaging without perturbing live cells. In this interference technique, performance can be very sensitive to both sample transmission and losses. This study shows that by balancing the nonlinear interferometer's arms, one can completely recover fringe visibility caused by signal loss. Moreover, intentional unbalancing offers a reduced-interaction regime where the detected power can be 200 times higher than the power reaching the sample, for ultrasensitive midinfrared sensing well below the conventional noise floor.

DOI
10.1103/physrevapplied.19.054019

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Sensing with undetected photons is a fascinating technique that allows imaging at wavelengths outside a particular detector's range---enabling, for example, biological imaging without perturbing live cells. In this interference technique, performance can be very sensitive to both sample transmission and losses. This study shows that by balancing the nonlinear interferometer's arms, one can completely recover fringe visibility caused by signal loss. Moreover, intentional unbalancing offers a reduced-interaction regime where the detected power can be 200 times higher than the power reaching the sample, for ultrasensitive midinfrared sensing well below the conventional noise floor.
Sensing with undetected photons enables the measurement of absorption and phase shifts at wavelengths different from those detected. Here, we experimentally map the balance and loss parameter space in a non-degenerate nonlinear interferometer, showing the recovery of sensitivity despite internal losses at the detection wavelength. We further explore an interaction-free operation mode with a detector-to-sample incident optical power ratio of >200. This allows changes in attowatt levels of power at 3.4 μμμm wavelength to be detected at 1550 nm, immune to the level of thermal black-body background. This reveals an ultra-sensitive infrared imaging methodology capable of probing samples effectively `in the dark'.
Quantum interference with undetected photons has gained significant attention in the past ten years due to its potential to decouple the probing and the detection of an active sensing system. The technique is based on correlated photon pairs: one photon interacts with the analyte, and the signature of the interaction is stored in its correlated counterpart. The probing photon remains undetected, while the other photon is measured. When the photons are highly non-degenerate, the spectral separation of the probing and detected photons offers significant advantages in terms of ease of operation and enhanced sensitivity, enabling more precise measurements and analysis with respect to other sensing techniques. This possibility enables a wide range of applications, particularly in fields such as imaging, spectroscopy, and optical coherence tomography, among others. This thesis describes experiments for imaging and sensing based on undetected photons, both in a free-space optical setup and in an integrated photonic circuit. The free-space configuration was used to perform undetected three-dimensional imaging reconstruction of diffusive targets. This validation of imaging with undetected photons paves the way to further development to in vivo biomedical imaging, covert imaging, and remote sensing. On the other hand, the integrated configuration overcomes the limitation of alignment tolerance and scalability of a free-space optical setup, enabling the development of integrated sensors based on undetected photons.
Abstract A typical imaging scenario requires three basic ingredients: (1) a light source that emits light, which in turn interacts and scatters off the object of interest; (2) detection of the light being scattered from the object and (3) a detector with spatial resolution. These indispensable ingredients in typical imaging scenarios may limit their applicability in the imaging of biological or other sensitive specimens due to unavailable photon-starved detection capabilities and inevitable damage induced by interaction. Here, we propose and experimentally realize a quantum imaging protocol that alleviates all three requirements. By embedding a single-photon Michelson interferometer into a nonlinear interferometer based on induced coherence and harnessing single-pixel imaging technique, we demonstrate interaction-free, single-pixel quantum imaging of a structured object with undetected photons. Thereby, we push the capability of quantum imaging to the extreme point in which no interaction is required between object and photons and the detection requirement is greatly reduced. Our work paves the path for applications in characterizing delicate samples with single-pixel imaging at silicon-detectable wavelengths.
Developing advanced technologies for sensing and imaging biological samples is crucial for medical applications, making quantum-enhanced methods particularly valuable, as they promise significant benefits over classical techniques. An important aspect of biological imaging is the characterization of tissue, which often involves resolving complex structural information such as birefringence and diattenuation. These measures require polarization-sensitive sensing which remains largely unaddressed in quantum-imaging techniques with undetected light. However, the bicolor nature and supreme phase sensitivity of nonlinear interferometers make them particularly advantageous for biological sensing. Hence, we theoretically introduce controllable polarizations of the interrogating light in a quantum-imaging setup and show the potential of nonlinear interferometers to simultaneously sense birefringence and diattenuation with undetected light while discussing both the low- and high-gain regime.
Quantum sensing with undetected photons is a technique where photons of one wavelength probe a sample, but information is extracted by measuring photons of another wavelength that never interacts with the sample. This has seen significant experimental advances in applications such as spectroscopy, microscopy, and bio-sensing. However, a detailed theoretical analysis using the tools of quantum metrology is currently lacking. Thus it is unclear how far away current schemes are from fundamental limits, and what the optimal measurement strategies are. We apply a multiparameter quantum estimation framework to quantify the error when estimating the unknown transmission and phase shift of a sample. The optimal measurement scheme is shown to require only a single controllable phase shift, easily implementable in existing setups. We also study how to use multipass interactions to maximise information gain. In general the optimum number of passes scales inversely with the log of the transmission of the sample. This work clarifies the metrological power of quantum sensing with undetected photons, and provides guidance for the design of experiments requiring high sensitivity.
Infrared (IR) imaging and spectroscopy is invaluable to many disciplines for its ability to probe molecular responses, from material analysis to diagnostic medicine. However, these applications are often limited by inefficient, noisy detectors. Non-degenerate nonlinear interferometers (NLIs) offer an alternative route through a technique known as imaging with undetected photons [1]. For an NLI producing visible-IR photon pairs, a change in the IR due to an object can be observed as a change to the interference of the visible photons. The IR does not need to be detected, bypassing the need for IR detectors completely.