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arXiv:2408.02531 · Advanced Quantum Technologies

Terahertz Quantum Imaging

Mirco Kutas, Felix Riexinger, Jens Klier, Daniel Molter, Georg von Freymann

Published Jun 11, 2025• 12 citations
arXivHTMLPDF

Abstract

Abstract Quantum imaging offers a powerful method for spatially transferring amplitude and phase information between spectral regions of interest, even when separated by several orders of magnitude in photon energy. However, so far demonstrations have been limited to regions of similar orders of magnitude in frequency, where commercial cameras are available. Here, amplitude‐ and phase‐sensitive imaging in the terahertz frequency region (1.5 THz) is demonstrated by detecting only visible photons (662.2 nm, 452.7 THz), separated by over two orders of magnitude. This allows reliable detection of terahertz information using a standard CMOS camera without cooling while still achieving spatial resolution close to the terahertz wavelength. The impact of strong noise contributions is reduced through quantum distillation.The experimental results are in good agreement with numerical simulations of the imaging process and demonstrate the huge potential of this method for exploring challenging spectral regions where conventional cameras are not available.

DOI
10.1002/qute.202500271

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Abstract Quantum imaging offers a powerful method for spatially transferring amplitude and phase information between spectral regions of interest, even when separated by several orders of magnitude in photon energy. However, so far demonstrations have been limited to regions of similar orders of magnitude in frequency, where commercial cameras are available. Here, amplitude‐ and phase‐sensitive imaging in the terahertz frequency region (1.5 THz) is demonstrated by detecting only visible photons (662.2 nm, 452.7 THz), separated by over two orders of magnitude. This allows reliable detection of terahertz information using a standard CMOS camera without cooling while still achieving spatial resolution close to the terahertz wavelength. The impact of strong noise contributions is reduced through quantum distillation.The experimental results are in good agreement with numerical simulations of the imaging process and demonstrate the huge potential of this method for exploring challenging spectral regions where conventional cameras are not available.
Modern terahertz detectors enable direct measurement of the electric field, providing simultaneous access to amplitude and phase information of the terahertz radiation. However, conventional systems are often based on single-pixel detectors, limiting most imaging applications to slow raster-scanning techniques. This work presents the demonstration of a novel approach for amplitude- and phase-sensitive imaging in the terahertz range using quantum imaging with undetected photons. By decoupling the sample measurement in the terahertz range from the detection of the information in the visible, this technique enables the use of cost-effective, highly developed multi-pixel optical components. Central achievements are the observation of quantum interference with terahertz photons and its application to material characterization and molecular concentration analysis. Furthermore, image information was transferred from the terahertz to the visible spectral range, achieving a spatial resolution close to the terahertz wavelength. This approach thus provides direct access to amplitude, phase, and spectral information for imaging applications in the terahertz range using a multi-pixel camera.
Quantum sensing is highly attractive for accessing spectral regions in which the detection of photons is technically challenging: Sample information is gained in the spectral region of interest and transferred via biphoton correlations into another spectral range, for which highly sensitive detectors are available. This is especially beneficial for terahertz radiation, where no semiconductor detectors are available and coherent detection schemes or cryogenically cooled bolometers have to be used. Here, we report on the first demonstration of quantum sensing in the terahertz frequency range in which the terahertz photons interact with a sample in free space and information about the sample thickness is obtained by the detection of visible photons. As a first demonstration, we show layer thickness measurements with terahertz photons based on biphoton interference. As nondestructive layer thickness measurements are of high industrial relevance, our experiments might be seen as a first step toward industrial quantum sensing applications.
Quantum sensing is highly attractive for accessing spectral regions in which the detection of photons is technically challenging: sample information is gained in the spectral region of interest and transferred via biphoton correlations into another spectral range, for which highly sensitive detectors are available. This is especially beneficial for terahertz radiation, where no semiconductor detectors are available and coherent detection schemes or cryogenically cooled bolometers have to be employed. Here, we report on the first demonstration of quantum sensing in the terahertz frequency range in which the terahertz photons interact with a sample in free space and information about the sample thickness is obtained by the detection of visible photons. As a first demonstration, we show layer thickness measurements with terahertz photons based on biphoton interference. As non-destructive layer thickness measurements are of high industrial relevance, our experiments might be seen as a first step towards industrial quantum-sensing applications.
Generation and Detection of terahertz radiation still remain a technological challenge, especially when compared to the visible or near infrared spectral range. For this reason, approaches are continuously pursued to transfer the terahertz radiation to other frequency ranges after interaction with the sample in order to utilize the advantages of the advanced detector technology. Novel quantum-optical concepts offer a further possibility to realize this transfer. This makes them an attractive alternative for the terahertz frequency range, as they only require cost-effective components such as visible continuous wave lasers and silicon-based detectors. We report on the first demonstration of imaging with undetected photons in the terahertz frequency range.
In quantum sensing experiments, photons in the spectral region of interest interact with a sample and their properties are transferred via biphoton-correlation to another spectral region, where widely available and highly developed detectors can be used. Especially spectral regions where the photon detection is quite difficult can benefit from this novel technique. We report on the first demonstration of quantum sensing in the terahertz frequency range, in which the terahertz photons interact with a sample in free space determining the thickness of polytetrafluoroethylene plates by only detecting visible photons [1].
Terahertz imaging has become increasingly important across various fields and practical production applications. Achieving both high sensitivity and high speed remains a primary challenge for most current THz imaging technologies. In this work, we present an imaging system based on Rydberg atomic vapor operating at frequencies exceeding 1 THz. By utilizing Cesium 133 atoms coupled with THz waves, de-excitation radiation generated after atomic excitation to Rydberg states converts invisible THz waves into visible light, enabling the acquisition of spatial information and intensity distributions of THz fields. The system achieves a minimum detectable power of 330 fW /s 1/2 per (2.4×2.4) μm 2 , an imaging resolution of approximately 1.7 mm, and an imaging bandwidth of 8.6 MHz. Additionally, the theoretical imaging rate can exceed 1 MHz. The Rydberg-atom-based THz imaging system exhibits a simple structure and is amenable to miniaturization. This THz imaging method holds promise for advancing applications in THz nondestructive testing, biomedical imaging, and concealed object detection.