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arXiv:2309.06777 · Quantum Science and Technology

Quantum optical induced-coherence tomography by a hybrid interferometer

Eun Mi Kim, Sun Kyung Lee, Sang Min Lee, Myeong Soo Kang, Hee Su Park

Published Dec 5, 2023• 11 citations
arXivHTMLPDF

Abstract

Abstract Quantum interferometry based on induced-coherence phenomena has demonstrated the possibility of undetected-photon measurements. Perturbation in the optical path of probe photons can be detected by interference signals generated by quantum mechanically correlated twin photons propagating through a different path, possibly at a different wavelength. To the best of our knowledge, this work demonstrates for the first time a hybrid-type induced-coherence interferometer that incorporates a Mach–Zehnder-type interferometer for near-visible photons and a Michelson-type interferometer for infrared (IR) photons, based on double-pass-pumped spontaneous parametric down-conversion. This configuration enables IR optical measurements via the detection of near-visible photons and provides methods for optimizing the quality of measurements by identifying photon pairs of different origins. We theoretically identify that the induced-coherence interference visibility is approximately the same as the heralding efficiency between twin photons along the relevant spatial modes, and experimentally maximize the visibility by setting up a common reference spatial mode for IR photons. Applications to both time-domain and frequency-domain quantum optical induced-coherence tomography for three-dimensional test structures are demonstrated. The results prove the feasibility of practical undetected-photon sensing and imaging techniques based on the presented structure.

DOI
10.1088/2058-9565/ad124d

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Abstract Quantum interferometry based on induced-coherence phenomena has demonstrated the possibility of undetected-photon measurements. Perturbation in the optical path of probe photons can be detected by interference signals generated by quantum mechanically correlated twin photons propagating through a different path, possibly at a different wavelength. To the best of our knowledge, this work demonstrates for the first time a hybrid-type induced-coherence interferometer that incorporates a Mach–Zehnder-type interferometer for near-visible photons and a Michelson-type interferometer for infrared (IR) photons, based on double-pass-pumped spontaneous parametric down-conversion. This configuration enables IR optical measurements via the detection of near-visible photons and provides methods for optimizing the quality of measurements by identifying photon pairs of different origins. We theoretically identify that the induced-coherence interference visibility is approximately the same as the heralding efficiency between twin photons along the relevant spatial modes, and experimentally maximize the visibility by setting up a common reference spatial mode for IR photons. Applications to both time-domain and frequency-domain quantum optical induced-coherence tomography for three-dimensional test structures are demonstrated. The results prove the feasibility of practical undetected-photon sensing and imaging techniques based on the presented structure.
Metrology with undetected photons is an emerging technique that leverages quantum effects and photon correlations (entanglement) to retrieve valuable information in a target spectral range (e.g., mid-infrared, mid-IR) using measurements in an easily accessible domain (e.g., visible, near-IR). The underlying quantum process of spontaneous parametric down-conversion (SPDC) is utilized to generate non-degenerate correlated signal and idler photons to serve as detection and probing photons, respectively. Sensing with undetected photons enables important advantages, such as ultra-low probe powers, room-temperature operation, and shot-noise-limited detection. In this contribution, we apply a quantum nonlinear interferometer based on an SPDC source to perform applied mid-IR spectroscopy, mid-IR microscopy, and mid-IR optical coherence tomography (OCT) as among the most promising techniques for quantum-based routine non-destructive testing. Moreover, we characterize the system, benchmark it against classical systems, and provide a prospective outlook for this new technology.
Optical coherence tomography (OCT) is an appealing technique for bio-imaging, medicine, and material analysis. For many applications, OCT in mid- and far-infrared (IR) leads to significantly more accurate results. Reported mid-IR OCT systems require light sources and photodetectors which operate in mid-IR range. These devices are expensive and need cryogenic cooling. Here, we report a proof-of-concept demonstration of a wavelength tunable IR OCT technique with detection of only visible range photons. Our method is based on the nonlinear interference of frequency correlated photon pairs. The nonlinear crystal, introduced in the Michelson-type interferometer, generates photon pairs with one photon in the visible and another in the IR range. The intensity of detected visible photons depends on the phase and loss of IR photons, which interact with the sample under study. This enables us to characterize sample properties and perform imaging in the IR range by detecting visible photons. The technique possesses broad wavelength tunability and yields a fair axial and lateral resolution, which can be tailored to the specific application. The work contributes to the development of versatile 3D imaging and material characterization systems working in a broad range of IR wavelengths, which do not require the use of IR-range light sources and photodetectors.
Quantum imaging with undetected light (QIUL) leverages the quantum correlations of photon pairs generated via spontaneous parametric down-conversion (SPDC) to retrieve both amplitude and phase information of an object. This method enables illumination and detection at distinct wavelength ranges, utilizing advanced detection technology in the visible spectrum while probing the object at an exotic wavelength. Here, we experimentally demonstrate a QIUL technique incorporating Fourier off-axis holography within a hybrid-type induced-coherence nonlinear interferometer. Our approach reconstructs the amplitude and phase information of an object in a single shot using a wide-field configuration, presenting a viable alternative to multi-frame acquisition techniques such as phase-shifting holography.
Optical coherence tomography (OCT) in the mid infrared (MIR) spectral range offers an elegant way of non-destructive optical testing of coatings that are opaque at visible and near infrared (NIR) wavelengths. However, light sources and detection equipment in the MIR are somewhat cumbersome due to low emission intensity and detectivity. Here we use spontaneous parametric down-conversion (SPDC) in a periodically poled KTP crystal pumped with 700 mW at 660 nm. The SPDC produces MIR photons near 3.8 µm and entangled NIR photons near 800 nm. All three wavelengths are used in a Michelson-type quantum interferometer. Only MIR photons interact with the device under test (DUT) and share their interference information with the NIR via the entanglement. The NIR photons are then analyzed with a conventional silicon-based spectrometer, thus, allowing MIR "sensing with undetected photons". We were able to shrink the quantum interferometer module to a footprint of 80 x 60 mm² including the 660 nm pump laser. The external MIR beam path offers a length of 235 mm ± 1.5 mm to the DUT and a single mode fiber port to the spectrometer. Using a mirror as a DUT we achieved a visibility of the quantum interference of up to 39%.
Parametric down-conversion is a second-order nonlinear optical process annihilating a pump photon and creating a pair of photons in the signal and idler modes. Then, by using two parametric down-converters and introducing a path indistinguishability for the two generated idler modes, a quantum coherence between two conjugate signal beams can be induced. Such a double spontaneous or stimulated parametric down-conversion scheme has been used to demonstrate quantum spectroscopy and imaging with undetected idler photons via measuring one-photon interference between their correlated signal beams. Recently, we considered another quantum optical measurement scheme utilizing W-type tripartite entangled signal photons that can be generated by employing three spontaneous parametric down-conversion crystals and by inducing coherences or path-indistinguishabilities between their correlated idler beams and between quantum vacuum fields. Here, we consider an extended triple stimulated parametric down-conversion scheme for quantum optical measurement of sample properties with undetected idler and photons. Noting the real effect of vacuum field indistinguishability on the fringe visibility as well as the role of zero-point field energy in the interferometry, we show that this scheme is an ideal and efficient way to create a coherent state of W-type entangled signal photons. We anticipate that this scheme would be of critical use in further developing quantum optical measurements in spectroscopy and microscopy with undetected photons.