Entangled photon pairs from semiconductor waveguides

bboall_c_smallEntanglement is a fascinating concept in quantum physics and a precious resource for quantum communication and computing. It is usually created in particle pairs, frequently by means of a conserved quantity in pair creation processes. The phenomenon is studied worldwide, as more and more complex entangled systems are utilized in quantum computation and communication protocols.

Quantum technologies are under intense research and development worldwide. One of them, quantum key distribution has matured far enough that it is a commercial reality, even though it can only establish secure keys over distances up to 50 km in fibers. This distance limitation can be overcome by the use of quantum repeaters, another quantum communication concept whose realization faces many obstacles.


Among these obstacles is the limited performance and physical size of current sources of entangled photon pairs. Traditionally these sources employ the phenomenon of spontaneous parametric down-conversion in nonlinear dielectric crystals. While a lot of progress has been made to implement waveguide sources in these nonlinear crystals, by their very nature they defy the idea of integrating the down-conversion with the required pump laser source.

BRW Pair Generation

In our project we exploit the same process of parametric down-conversion, but implement it in semiconductors, for example using Bragg-reflection waveguides (BRW). We have acquired in-depth knowledge about the peculiarities in design and operation of such a photon pair source. Together with the independent demonstration of an integrated laser, this opens a perspective towards an all-integrated source of entanglement. We focus not only on the engineering and optimization of the BRWs, but also investigate the quantum-optical properties of the down-converted photon pairs and employ them in further experiments.

The possible impact of our research is tremendous. An on-chip source of entanglement will not only allow the development of improved entanglement-based quantum key distribution systems with tiny components, but also enable previously impossible quantum optics experiments by allowing much more complex combinations of sources and detectors. Finally we can envision a complete quantum optics lab on a chip, where lasers, linear and nonlinear elements as well as detectors can all be built in one package.


A. Schlager, M. Götsch, R. J. Chapman, S. Frick, H. Thiel, H. Suchomel, M. Kamp, S. Höfling, C. Schneider, and G. Weihs, Difference-frequency generation in an AlGaAs Bragg-reflection waveguide using an on-chip electrically-pumped quantum dot laser, Journal of Optics 23, 085802 (2021). DOI: 10.1088/2040-8986/ac13ae

S. Auchter, A. Schlager, H. Thiel, K. Laiho, B. Pressl, H. Suchomel, M. Kamp, S. Höfling, C. Schneider, and G. Weihs, Understanding photoluminescence in semiconductor Bragg-reflection waveguides, J. Opt. 23 (2021), DOI: 10.1088/2040-8986/abd888

K. Laiho, M. Schmidt, H. Suchomel, M. Kamp, S. Höfling, C. Schneider, J. Beyer, G. Weihs, and S. Reitzenstein, Photon-number parity of heralded single photons from a Bragg-reflection waveguide reconstructed loss-tolerantly via moment generating function, New J. Phys. 21, 103025 (2019), DOI: 10.1088/1367-2630/ab42ae 

H. Chen, K. Laiho, B. Pressl, A. Schlager, H. Suchomel, M. Kamp, S. Höfling, C. Schneider, and G. Weihs, Optimizing the spectro-temporal properties of photon pairs from Bragg-reflection waveguides, J. Opt. 21, 054001 (2019), DOI: 10.1088/2040-8986/ab0fe9 

H. Chen, S. Auchter, M. Prilmüller, A. Schlager, T. Kauten, K. Laiho, B. Pressl, H. Suchomel, M. Kamp, S. Höfling, C. Schneider, and G. Weihs, Time-bin entangled photon pairs from Bragg-reflection waveguides, APL Photonics 3, 080804 (2018). DOI: 10.1063/1.5038186 

B. Pressl, K. Laiho, H. Chen, T. Günthner, A. Schlager, S. Auchter, H. Suchomel, M. Kamp, S. Höfling, C. Schneider, and G. Weihs, Semi-automatic engineering and tailoring of high-efficiency Bragg-reflection waveguide samples for quantum photonic applications, Quantum Science and Technology 3, 024002 (2018), DOI: 10.1088/2058-9565/aaa2a2

A. Schlager, B. Pressl, K. Laiho, H. Suchomel, M. Kamp, S. Höfling, C. Schneider, and G. Weihs, Temporally versatile polarization entanglement from Bragg reflection waveguides, Optics Letters 42, 2102 (2017), DOI: 10.1364/OL.42.002102

K. Laiho, B. Pressl, A. Schlager, H. Suchomel, M. Kamp, et al., Uncovering dispersion properties in semiconductor waveguides to study photon-pair generation, Nanotechnology 27, 434003 (2016), DOI: 10.1088/0957-4484/27/43/434003

B. Pressl, T. Günthner, K. Laiho, J. Geßler, M. Kamp, S. Höfling, C. Schneider, and G. Weihs, Mode-resolved Fabry-Perot experiment in low-loss Bragg-reflection waveguides, Opt. Express 23, 33608 (2015), DOI: 10.1364/OE.23.033608

T. Günthner, B. Pressl, K. Laiho, J. Geßler, S. Höfling, M. Kamp, C. Schneider, and G. Weihs, Broadband indistinguishability from bright parametric downconversion in a semiconductor waveguide, Journal of Optics 17, 125201 (2015), DOI: 10.1088/2040-8978/17/12/125201

M. Covi, B. Pressl, T. Günthner, K. Laiho, S. Krapick, C. Silberhorn, and G. Weihs, Liquid-nitrogen cooled, free-running single-photon sensitive detector at telecommunication wavelengths, Appl. Phys. B 118, 489 (2015), DOI: 10.1007/s00340-015-6019-y

B. Pressl, G. Weihs, Notes on evanescent wave Bragg-reflection waveguides, in Emerging Technologies in Security and Defence; and Quantum Security II; and Unmanned Sensor Systems X, 88990Q. DOI: 10.1117/12.2030833

R. Horn, P. Abolghasem, B. J. Bijlani, D. Kang, A. S. Helmy, and G. Weihs, Monolithic Source of Photon Pairs, Phys. Rev. Lett. 108, 153605 (2012), DOI: 10.1103/PhysRevLett.108.153605

Follow-up projects

  • UNIQORN: Affordable Quantum Communication for Everyone: Revolutionizing the Quantum Ecosystem from Fabrication to Application
  • Beyond-C: Integrated Quantum Photonics
  • IGUANA: Integrated Quantum Rangefinding
  • D-A-CH: On-chip microlaser driven sources of indistinguishable photons for quantum network


  • FWF DACH project  “Integrated Sources of Entangled and Indistinguishable Photons” together with C. Schneider (U Würzburg) and S. Reitzenstein (TU Berlin) ((I-2065, DACH Project, 2015-2018)
  • K. Laiho is supported by the FWF Erwin-Schrödinger-Fellowship
    Project “Counting photons from Bragg-reflection waveguides” (J-4125, 2017-2019)
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