Imaging with quantum phenomena
With interesting and novel rules quantum physics open up a new world for various applications, for example in the areas of communication, sensor technology and computing. Due to intensive research in the field of quantum technologies, impressive progress has been achieved in recent years. This is also true for the domain of quantum imaging.
This process uses the quantum physical phenomenon of the entangling of photons to exceed the limits of the classical imaging processes and to enable new applications. From a pair of entangled photons only one photon is detected. But through the entanglement conclusions about the features and interactions of the not detected photon can be drawn. Thus, an object can be depicted without being in interaction with the detected photons (therefore: “ghost imaging”).
Apart from the curiosity and fascination of this phenomenon, it is also of great interest for several applications. One big advantage is the decoupling from external influences through the detection of undisturbed photons instead of the actual interactive photons. In the generation of the photon pairs the entangled photons can have different wavelengths. This option allows for the exploitation of the benefits and features of both wavelength ranges and therefore the access to interactions that can’t be reached by classic processes.
For example, in spectroscopic quantum imaging applications the interactions of photons in the medium infrared range (MIR, approx. 3-15 µm) with molecules can be determined through the entangled photons in the visible range with the help of common detectors. In the other direction the access to extremely short wavelengths (UV) is interesting for microscopic applications to reach an increases resolution with non-destructive measurement, while the entangled photons in the visible range can be detected conventionally.
Because the entanglement between the single photons occurs, these innovative approaches of quantum imaging require an extremely sensitive and efficient detector technology. For an error-free correlation of the detected entangled photon pairs an equally high temporal resolution is necessary as well. These high requirements make the SPAD detector technology to the preferred candidate in several applications.
The CMOS-integrated SPADs (CSPAD) of Fraunhofer IMS achieve a very high temporal resolution due to the short dead time. The low dark count rate and high quantum efficiency ensure a high sensitivity up to the single photon. Detectors manufactured at IMS with SPAD arrays therefore exhibit the optimal features to allow for a detection of single photons both spatially and temporally resolved. In the in-house CMOS technology developed and realized read out circuits can be individually customized to the application.
Within the framework of the Fraunhofer lead project QUILT (Quantum Methods for Advanced Imaging Solutions) Fraunhofer IMS and five other Fraunhofer institutes make progressive, scientific contributions in several research areas of quantum imaging. Because of the combined expertise of the institutes and proactive approach, the Fraunhofer-Gesellschaft is to become the most important player in the quantum optical application research. The development, production and optimization of single photon detectors with SPAD technology of Fraunhofer IMS are elemental components of the project.