Terahertz quantum sensing

Abstract

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.

Fourier transform infrared spectroscopy with visible light

“…This allows the usage of a silicon based detector and a visible laser light source, which circumvents the usage of expensive, cryogenically cooled infrared detectors. The demonstrated measurement technique can easily be applied to the whole infrared transparency range of lithium niobate; possibly it could be extended to the terahertz regime [11,12]. The usage of other nonlinear materials allows the extension of the technique to the far infrared.…”

Quantum Fourier-Transform Infrared Spectroscopy for Complex Transmittance Measurements

“…The detection bandwidth can be significantly improved, combined with a broadband photon-pair source [37,38]. The operating wavelength of QFTIR spectroscopy could be extended to the mid-and far-infrared regions by choosing a suitable nonlinear crystal as the photon-pair source [39][40][41][42]. Our method can be applied to a variety of quantum spectroscopy systems, such as those based on a Mach-Zehnder nonlinear interferometer, with minor modifications, and is also applicable for infrared hyperspectral imaging [43].…”

Induced Coherence via Spontaneous Four‐Wave Mixing in Atomic Ensembles

“…[ 3–10 ] Recently, the induced‐coherence concept has been extended to nonlinear interferometers, [ 11–13 ] entanglement of two spatially separated atomic ensembles, [ 14 ] quantum imaging with undetected photons, the complementarity principle, and quantum spectroscopy. [ 15–22 ]…”