Setup for quantum imaging with undetected photonics.
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Quantum-Enhanced Imaging

Dr. Markus GRÄFE
Setup for quantum imaging with undetected photonics.
Image: Fraunhofer IOF
Dr. Markus Gräfe Dr. Markus Gräfe Image: Anne Günther (University of Jena)

Dr. Markus GRÄFE

Email: markus.graefe@iof.fraunhofer.de, markus.graefe@uni-jena.de
Phone: +49 3641-807-361

Dr. Markus Gräfe finished his PhD in the field of integrated quantum photonics at the Institute of Applied Physics in Jena in 2017. For his outstanding contributions in the field of photonic quantum walks he was awarded with the Applied Photonics Award (STIFT Förderpreis). He is a group leader at the Fraunhofer Institute for Applied Optics and Precision Engineering IOF for »Quantum-Enhanced Imaging« and related quantum photonics areas within the Emerging Technologies Department.  Together with the Bundesamt für die Sicherheit der Informationstechnik Dr. Gräfe organized two workshops on quantum random number generation. In 2021 he became group leader of the »Quantum Photonics & Sensing Group« at the Institute of Applied Physics in Jena. 

Research Areas

Photonics is one of the main enablers for quantum technology. In this context non-classical states of light, in particular photon pairs, allow novel concepts for imaging and sensing beyond classical limitations. Moreover, as quantum information carriers, photons are the essential building block for photonic quantum simulation and computing. Dr. Gräfe’s research focusses on entanglement, correlation, and interferometer based quantum imaging techniques as well as on integrated quantum photonics including quantum walks of photon pairs and their non-classical correlations. His research topics include:

  • Quantum imaging and sensing with undetected photons
  • Microscopy with non-classical states of light
  • Photon-pair and multi-photon source development
  • Quantum walks of correlated photon pairs and multiphoton states
  • Entropy sources and quantum random number generation

Teaching Fields

Dr. Gräfe currently teaches the following Master courses at the Friedrich Schiller University Jena:

  • Quantum imaging and sensing
  • Integrated quantum photonics

Research Methods

The following methods and equipment are harnessed in the group:

  • Photon pair sources based on spontaneous parametric down conversion
  • Non-linear interferometers for induced coherence
  • Contiuous-wave and pulsed laser systems at various wavelengths
  • Single photon detectors and correlation electronics
  • Linear and non-linear waveguide characterization
  • Entangled two-photon absorption

Recent Research Results

Harnessing photon pairs from spontaneous parametric down conversion allows to make use of nonclassical properties of such quantum states. This can be of particular interest in the fields of imaging, microscopy, and sensing, since it allows new modalities extending the possibilities of classical techniques [1]. In doing so, it bec comes possible to spectrally separate illumination of a specimen and the actual detection on the camera by so-called imaging with undetected photons. One major step is advancing this technique towards a portable system capable of video rate imaging at long-term stability [2]. Moreover, demonstrating holography with undetected light brings three-dimensional imaging in exotic spectral ranges within reach [3]. In addition, two-photon fluorescence can be driven by photon pairs with the advantage of having a linear absorption response with respect to a quadratic one in the classical domain. This beneficial behavior (more fluorescence light at same excitation level) allows longer observation of light-sensitive biosamples. The pioneering demonstration of the linear absorption rate for convenient fluorophores was demonstrated [4].

Further, the fundamental limits of the quantum random number generation rate using the phase noise of gain-switched pulsed lasers was investigated. An essential conclusion is an upper limit of the repetition rate for independent, and thus, high-quality random numbers [5].

Quantum walks of photonic states in integrated networks are the implementation tool for quantum simulation and quantum gate operations [6]. In this field many contributions have been made, such as the recent demonstration of an on-chip quantum state tomography tool [7], a heralded CNOT quantum gate [8], and the investigation of quantum coherence endurance in noisy environments [9]. Some of this works did benefit from an advanced fabrication technique of quantum photonic chips that allows better mode matching, and thus lower loss, for interconnecting with optical fibers [10].

[1] Gilaberte Basset et al., Laser Photon. Rev. 13, 1900097 (2019).
[2] Gilaberte Basset et al., Laser Photon. Rev. 15, 2000327 (2021).
[3] Töpfer et al., in preparation (2021).
[4] Gäbler et al., in preparation (2021).
[5] Septriani et al., AIP Advances 10, 055022 (2020).
[6] Gräfe et al., J. Phys. B 53, 073001 (2019).
[7] Titchener et al., npj Quantum Information 4, 19 (2018).
[8] Zeuner et al., npj Quantum Information 4, 13 (2018).
[9] Perez-Leija et al., npj Quantum Information 4, 45 (2018).
[10] Heilmann et al., Appl. Opt., 57, 377 (2018).

link to the introduction of the Gräfe research group at Fraunhofer IOF

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