To realize quantum-enhanced imaging, we are using a method called Quantum Ghost Imaging. It is based on photon pairs, typically generated by spontaneous parametric down-conversion in nonlinear optical materials. The two photons of a pair are separated and one of them is used to illuminate the sample under test. After interaction with the sample, this photon is measured with a single detector without any spatial resolution. The second photon is imaged onto a single-photon sensitive camera, where its spatial position can be measured. However, this photon does not see the sample. From the individual measurements of each of the detectors, no image of the sample can be obtained. However, due to the non-classical correlations between the two photons of each pair, the image can be reconstructed by correlating the measurements of both detectors.

This measurement approach enables to generate images using only very small photon fluxes, which makes it especially promising for sensitive samples. Furthermore, the separation of spatially sensitive detection channel and sample interaction allows to use photons of different wavelength for both of them, thus enabling imaging in spectral ranges where no camera is available. Finally, potentially more information can be obtained within one measurement when different properties of both photons are measured, e.g. by supplanting the single detector with a more complex detection system. We are investigating the fundamental properties and different implementations of Qantum Ghost Imaging with the aim of applying it to measurement problems e.g. in the life sciences.

Furthermore, we are studying different approaches to realize quantum-enhanced spectroscopy techniques. Similar to Ghost Imaging, spectroscopy with very small photon numbers can be realized based on the spectral correlations of the photons of a pair. Here, the spatially-resolving detector is replaced with a spectrally-resolving one. Additionally, we are also investigating measurement approaches, where only the photon not interacting with the sample is detected using one detector. The photon interacting with the sample is not measured and the information about the sample properties is imprinted on the measured photon using quantum interference. This scheme would enable to measure in spectral ranges where no detector at all exists.

  • A. S. Solntsev, P. Kumar, T. Pertsch, A. A. Sukhorukov, and F. Setzpfandt, "LiNbO3 Waveguides for Integrated Quantum Spectroscopy," APL Photonics 3, 021301 (2018)

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