Roughly since 2021, quantum sensing techniques have enabled precision measurements in material science and fundamental physics beyond classical state-of-the-art solutions. The reason for this is the increased number of degrees of freedom to shape light and effectively exploit its extended properties of quantum optical states for real-life measurements. At RECENDT, we aim to advance these techniques and turn them into well-established Non-Destructive Testing (NDT) methods.
Quantum Sensing
Introduction
The concept of the use of entangled photons for non-linear interferometry
The concept of bi-photon interferometry
Induced coherence (of correlated photon sources) without induced emission: a common pump (λp) illuminates two nonlinear crystals (triggering SPDC processes) (SPDC: spontaneous parametric down-conversion), generating correlated or entangled photon pairs (λs and λi). The information on which photon comes from which source is erased at the second crystal (SPDC2). As a result, interference can be observed for the photons of the first and second SPDC source due to the indistinguishability of the photon paths (the idler and signal paths have to have identical length). The interferometer can therefore be used for sensing with undetected photons, as the interference pattern (akin to conventional interference) can be detected using photons that never interacted with the sample T.
This enables the realization of "metrology with undetected photons". Since the wavelengths of the idle and signal photons (in the case of the non-degenerate SPDC) can be spectrally widely separated, e.g. mid-infrared measurements can be performed using high-sensitivity near-infrared detectors, making these methods of great interest for various applied scenarios in research and industry.
Our vision
RECENDT's vision is to turn Quantum technology into next generation NDT tools with unprecedented sensitivity and benefits for industrial application.
The current focus is on the development of methods based on non-linear interferometers.
- Principle:
⇒ Broadly non-degenerate entangled photon pairs are generated in spontaneous parametric down-conversion (SPDC)
⇒ Those pairs of entangled photons are used for "sensing with undetected photons"
⇒ The entanglement of photons (e.g., near- and mid-IR twins) allows to use the MIR-photon to probe the sample, while the NIR-photon is used for detection
- Advantages:
⇒ Significant technological advantages because probing and detection are decoupled from each other
⇒ Typically troublesome and expensive mid-IR measurements are replaced by measurements in the NIR domain
⇒ Well-developed and significantly cheaper silicon-based detectors can be applied in the near-infrared spectral range
⇒ Eliminating the limits and difficulties that exist for traditional systems
⇒ Unique possibilities for high-sensitivity and high-resolution measurements in typically challenging scenarios
⇒ Cost-effective components
Since the nature of non-linear interferometry is akin and quite similar to the classical technology, i.e. based on cross-correlation, this quantum sensing approach can be seamlessly implemented, e.g., in OCT, microscopy, and Fourier-transform mid-IR spectroscopy, as the basic principles are the same.
Quantum Optical Coherence Tomography (Q-OCT)
Outlook, perspectives & goals
Optical quantum sensing techniques clearly have the potential to revolutionize the way complex and difficult measurements are performed, leading to advances in industry and research areas such as biomedicine, basic and applied physics, and chemistry.
So far, the major research in this area has been focused on improving non-linear crystals and SPDC (spontaneous parametric down-conversion) sources, investigating and optimizing phase-shifting schemes, and extending the spectral range.
At RECENDT, we aim to ensure that these new sensing methods find their place in a wide field of NDT solutions. We further develop, optimize, apply, and benchmark them in practice. Close cooperation with other research groups and a solid application-related background are particular advantages.
TV-coverage on Quantum Sensing activities at RECENDT
Possible Applications
Spatially resolved spectroscopy
Do you want to know the exact local distribution (in micrometer range) of your chemical components? With Mid-Infrared-Microscopy we can chemically characterize and measure materials and cross-sections (e.g. residues or inclusions) with a spatial resolution as small as 5 µm. Quantum Sensing offers interesting opportunities in that area too.
Spectroscopic imaging
The spectroscopic control of chemical compoundings (e.g. of pills) can be achieved by implementing different technologies (NIR, MIR, Raman, THz and also Quantum Sensing). Spatially resolved spectroscopy is also possible – moreover you can get a picture, for instance, of the API (Active Pharmaceutical Ingredient) distribution in the product!
Inner structures in high-scattering materials
You need to inspect inner structures in, e.g., industrial ceramics, filled polymers or paints, composite materials? Often, this inspection task is hindered by the intense scattering effects. By applying mid-infrared OCT (Optical Coherence Tomography) or our latest Quantum Sensing technologies, we can overcome those problems and provide an increased probing depth and still 8 µm axial resolution.
