Kai Müller

Photonic Quantum Engineering

Technical University Munich

Walter Schottky Institut

Am Coulombwall 4

85748 Garching

Tel. +49 89 289 12772


Group Webpage

Entanglement is amazing, let’s make use of it.


Research focus: photonic quantum technologies - from fundamentals to applications

Since photons travel with the speed of light and experience low losses, they are excellent carriers for quantum information and enable a broad range of photonic quantum technologies. Our group explores light-matter interactions at the nanoscale to realize all key ingredients which are essential for the generation, manipulation and detection of quantum states of light. Examples for such quantum states are single photons or photons entangled with other photons or spin-qubits. In future applications, the individual building blocks will either be integrated in a single chip to realize fully-integrated quantum photonic circuits or form modular building blocks for distributed quantum technologies.

Examples for these building blocks are non-classical light sources, spin-photon interfaces, quantum memories and single-photon detectors. Since every quantum system has specific advantages and disadvantages we investigate a breath of systems including semiconductor quantum dots, color centers in diamond, two-dimensional transition metal dichalcogenides and rare-earth ions embedded in complex oxide crystals. Our research spans the full range from fundamentals to applications. This includes for example the investigation of novel quantum materials, development of quantum optical techniques, design and fabrication of nanophotonic structures and quantum engineering of building blocks and devices. Examples for targeted applications include quantum communication, distributed quantum networks and quantum simulation and metrology based on photons.

Selected publications

  • L. Hanschke, K. A. Fischer, S. Appel, D. Lukin, J. Wierzbowski, S. Sun, R. Trivedi, J. Vuckovic, J. J. Finley, K. Müller, “Quantum dot single photon sources with ultra-low multi-photon probability”, npj Quantum Information 4, 43 (2018).
  • K. A. Fischer, L. Hanschke, J. Wierzbowski, T. Simmet, C. Dory, J. J. Finley, J. Vuckovic, K. Müller, “Signatures of two-photon pulses from a quantum two-level system”, Nature Physics 13, 649–654 (2017).
  • K. Müller, K. A. Fischer, C. Dory, T. Sarmiento, K. G. Lagoudakis, A. Rundquist, Y. Kelaita, J. Vuckovic, “Self-homodyne-enabled generation of indistinguishable photons”, Optica 3, 931-936 (2016).
  • K. Müller, K. A. Fischer, A. Rundquist, C. Dory, K. G. Lagoudakis, T. Sarmiento, Y. A. Kelaita, V. Borish, J. Vuckovic, “Ultrafast Polariton-Phonon Dynamics of Strongly Coupled Quantum Dot-Nanocavity Systems”, Physical Review X 5, 031006 (2015).
  • K. Müller, A. Rundquist, K. A. Fischer, T. Sarmiento, K. G. Lagoudakis, Y. A. Kelaita, C. Sánchez Muñoz, E. del Valle, F. P. Laussy, J. Vuckovic, “Coherent Generation of Nonclassical Light on Chip via Detuned Photon Blockade”, Physical Review Letters 114, 233601 (2015).


Site-selectively generated photon emitters in monolayer MoS2 via local helium ion irradiation

J. Klein, M. Lorke, M. Florian, F. Sigger, J. Wierzbowski, J. Cerne, K. Müller, T. Taniguchi, K. Watanabe, U. Wurstbauer, M. Kaniber, M. Knap, R. Schmidt, J. Finley, A. Holleitner.

Nature Communications 10, Article number: 2755 (2019).

Show Abstract

Quantum light sources in solid-state systems are of major interest as a basic ingredient for integrated quantum photonic technologies. The ability to tailor quantum emitters via site-selective defect engineering is essential for realizing scalable architectures. However, a major difficulty is that defects need to be controllably positioned within the material. Here, we overcome this challenge by controllably irradiating monolayer MoS2 using a sub-nm focused helium ion beam to deterministically create defects. Subsequent encapsulation of the ion exposed MoS2 flake with high-quality hBN reveals spectrally narrow emission lines that produce photons in the visible spectral range. Based on ab-initio calculations we interpret these emission lines as stemming from the recombination of highly localized electron–hole complexes at defect states generated by the local helium ion exposure. Our approach to deterministically write optically active defect states in a single transition metal dichalcogenide layer provides a platform for realizing exotic many-body systems, including coupled single-photon sources and interacting exciton lattices that may allow the exploration of Hubbard physics.

DOI: 0.1038/s41467-019-10632-z

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