»Quantum sensing« describes the measurement of physical quantities using the specific properties of isolated quantum systems. These can be atoms in specifically prepared electronic states, localized states in solids or photons that are "entangled" with each other in their properties. For methodical reasons, quantum sensors and measurement systems based on them are usually more complicated in their construction than classical sensors. Nevertheless, they may offer significant advantages in terms of sensitivity and measurement accuracy: The development of atomic clocks based on ultracold atoms is the most famous example for this.
Non-linear interferometers with entangled photons for infrared measurement technique
Spectroscopic information on molecules, chemical compounds and organic substances is often available in the mid infrared. However, detectors in this spectral range are technologically complex and expensive, and they often require cryogenic cooling. The generation of entangled photon pairs in non-linear interferometers is an alternative approach: Pairs consisting of a visible and an infrared photon are used. The infrared photons interact with the sample; in the interferometer, the information is transferred to the visible photons and can be detected easier and faster with silicon-based detectors. The development of such non-linear interferometers - from quantum optical basic research to the demonstration of applications - is the topic of the work in the Lighthouse project QUILT at Fraunhofer IPM.
Optically pumped magnetometers
The frequencies of optical transitions in atoms can be measured with very high accuracy - this is what the new generations of atomic clocks are based on. Again, the precondition is that the atoms are placed in certain quantum (spin-) states in a controlled manner. External influence can shift the transition frequencies. What would have a deteriorating effect for a clock can now be used in the construction of highly sensitive quantum sensors, e.g. for measuring very weak magnetic fields. These optically pumped magnetometers (OPM) with alkali atoms have the potential to replace the state-of-the-art superconducting sensors, which require expensive cooling. As part of the Lighthouse project QMAG, Fraunhofer IPM is investigating the implementation of such sensors in fields like process analysis and material studies.