The Thuringian Innovation Center for Quantum Optics and Sensor Technology (InQuoSens) at the locations Jena and Ilmenau intends to use the current call of the Thüringer Aufbaubank (TAB) for funding of the research group FOQUOS to strategically strengthen its position in the research and innovation field of quantum technologies. Based on existing competencies in the field of imaging opto-electronic systems and quantum optics, the research group will concentrate on the development of basic technologies and demonstrators for applications in quantum imaging in application-relevant spectral ranges. This topic area was identified as particularly promising in terms of its innovation potential in a preliminary study by InQuoSens. In addition, the research and innovation field of quantum technologies was identified by Thuringian representatives from industry, science and politics within the responsible working group of the Regional Research and Innovation Strategy for Intelligent Specialization for Thuringia ("RIS3 Thuringia")1 as one of the most relevant future fields for the future development of the Free State. The FOQUOS research group therefore directly takes up the strategy process defined by the RIS3 guideline as a guideline for action.
At the same time, the project is of exceptionally high national and international importance, as extensive funding initiatives on the future topic of quantum technologies have recently been launched at both federal and EU level in the form of "Quantum Technology - Fundamentals and Applications" (QUTEGA) and the "Quantum Technologies Flagship" (QUTE-F). Thuringia is enabled by the work within InQuoSens and FOQUOS to make substantial contributions within these initiatives in the future. Last but not least, the research group will contribute to a broad and sustainable expertise in the form of highly qualified junior staff in the Free State of Thuringia by being embedded in the academic environment of the Universities of Jena and Ilmenau, where research results in quantum optics and technology will be directly integrated into the academic education on master and doctoral level.
The applications addressed in the project use the specific quantum properties of entangled photon pairs. These form a common quantum state, which allows information about e.g. the location of one of the photons to be obtained by measuring the partner photon. This property can be used to realize optical measurement techniques with spatial resolution, in which one of the photons of a pair interacts with the object to be measured, but only the other photon is measured by a spatially resolving camera. This approach called ghost imaging has already been demonstrated experimentally [Mor15]. The outstanding application potential of measurement procedures based on this method results from the possibility to use photon pairs in which the two photons have substantially different wavelengths. The properties of the object are measured at the wavelength of the photon interacting with the object, but the wavelength of the second photon can be adapted, for example, to the optimum working wavelength of the camera used. Furthermore the achievable spatial resolution depends in a complex way on the wavelengths of both photons and can be larger for certain cases than would be possible for the wavelength of the photon interacting with the object in classical optical measuring methods. These advantages are particularly useful when the wavelengths of the individual photons of the entangled photon pair are far apart.
The aim of the FOQUOS research group is to experimentally verify the potential of ghost imaging, which has so far only been shown in very basic experiments or simplified theoretical models, for two specific highly relevant applications, and to quantitatively determine the performance parameters and limiting factors of these imaging methods, which are important for potential commercial applications. In particular, the following two use cases will be investigated:
Imaging and imaging spectroscopy in the mid infrared (MIR):For the MIR spectral range from 2 μm to 10 μm wavelengths, only very limited sensitive and high-resolution cameras exist. By using ghost imaging, the need for such cameras can be avoided. For this purpose, photon pairs with very different wavelengths are used, one of which lies in the visible spectral range (VIS), the other in the MIR. The MIR photon interacts with the object to be measured and is then detected by a single detector. The VIS photon is measured with a high-resolution camera, which works very efficiently in this spectral range and has practically no noise. Thus, images in the MIR can be reconstructed in high quality even at very low optical powers. By using another spontaneous parametric down-conversion (SPDC) process, MIR detectors can even be dispensed with completely. For this purpose, the MIR photon is also converted to VIS after interaction with the sample [Lem14].
Imaging with extreme resolutions in short wavelength spectral ranges:The resolution of optical imaging can be greatly increased by using light in the short-wave ultraviolet or X-ray (XUV) range with wavelengths of a few 10 nm. However, biological samples in particular are unsuitable for irradiation with XUV light and are destroyed in the imaging process by the high photon energy. When using ghost imaging with photon pairs of XUV and VIS photons, this optical damage can be prevented if the sample only interacts with the VIS photons. The very high resolving power of the short wavelength XUV photons can still be used [Li15].
For both approaches, the research group will realize demonstrator experiments to demonstrate the application relevance. For this purpose, fundamental theoretical preliminary investigations must first be carried out in order to identify optimal parameters for the demonstrators and to determine the influence of all experimental boundary conditions on the measurement procedures. Furthermore, two important basic technologies must be further developed. These are on the one hand optimized sources for photon pairs in the addressed spectral ranges and specific control and evaluation electronics for the detectors used. Based on these basic technologies, the demonstrators will allow an experimental verification of all parameters of ghost imaging systems relevant for applications as well as an estimation of the necessary development effort for commercial exploitation.
