Quantum Photonics

In nano-sized optical devices, light-matter interactions can be made so strong that quantum mechanical effects are decisive. The main focus of the Quantum Photonics Group is on techniques to control the quantum dynamics of quantum dots interacting with photons.

In this way we can fabricate light sources that emit single photons on demand, or entangle quantum dots and photons. Such nanophotonic devices will find applications for quantum information purposes and provide a route towards scalable quantum computing. In addition to developing and testing novel devices, we explore the fascinating fundamental physics of light and matter confined to the nano-scale.

Solid-state quantum simulators for biochemistry (SolidQ)

Solid-Q is a new joint research consortium generously funded by the Novo Nordisk Foundation that the Quantum Photonics group is proud to be a part of. Solid-Q unites two leading solid-state experimental platforms and applies them to problems in quantum chemistry and material science. An overarching goal is to characterize and eventually control charge, energy, and heat transport of relevance for molecular reactions, material design, and quantum coherent transport in light harvesting complexes. Ultimately our goal is to simulate protein folding problems of relevance for drug discovery with a quantum advantage.

Read more about SolidQ

Scalable quantum photonic devices

Quantum photonics relies on the efficient and controlled generation of single photons for processing and exchanging quantum information across different nodes in a solid-state or hybrid quantum network. One of the main advantages of a solid-state platform is the possibility to integrate emitters such as semiconductor quantum dots (QDs) with nanophotonic circuits in a single chip, to build scalable quantum information processing devices. A challenging task in this direction is to scale photonic devices to perform experiments involving several quantum bits (or qubits).

Read more about Scalable quantum photonic devices

Quantum information processes with coherent single-photon sources

Quantum physics enables communication and computation protocols that promise superior performance and security in comparison to the widely used classical methods. This promise has led to a widespread interest and a rapid surge towards realizing quantum technologies. Among the variety of physical systems that are being explored, Quantum Photonics is a natural choice for communication due to the ease and robustness of encoding information onto photons. Working at this exciting juncture of time on state-of-art single photon sources, we are currently delving into device-independent quantum cryptography protocols for secure communication including random number generation (QRNG) and quantum key distribution (QKD).

Read more about Quantum information processes

Nanofabrication

Controlling and manipulating single photons at the chip scale requires state-of-the-art nano-fabrication techniques. The Quantum Photonics group has developed over the past years advanced processing methods for building nanostructures in gallium arsenide (GaAs) with tailored optical properties. These include passive devices such as waveguides, photonic crystals, and gratings, but also active electro-optic structures.

Read more about Nanofabrication

Controlling quantum light-matter interaction in photonic nanostructures

It is well known that the spontaneous emission of a quantum emitter depends not only on the intrinsic properties of the emitter, but also on the density of vacuum fluctuations surrounding the emitter.

Read more about quantum light-matter interaction

Multiphoton entanglement using quantum dot spins

The ability to send quantum information over long distances would allow a number of quantum technologies such as Quantum Key Distribution for secure commination. However, sending information encoded as photons quickly becomes insurmountable over long distances due to photon loss. A possible solution to this problem is the One Way Quantum Repeater: Rather than sending a single photon the entire distance, a so-called cluster state consisting of multiple entangle photons is sent through a chain of repeater stations. At each repeater station the quantum information is transferred onto a “fresh” cluster state, and the gradual photon loss is thus overcome

Read more about Multiphoton entanglement

Quantum nonlinear optics

Photons usually interact very weakly with each other. This makes photons very well suited as carriers of quantum information in quantum communication. However, for many advanced quantum applications two-qubit gates are required, which requires nonlinear photon-photon interaction. An efficiently coupled quantum dot (QD) to a nanophotonic cavity or waveguide can mediate such a single-photon nonlinear operation since the QD can only scatter a single photon at a time, meaning that it responds very differently to one or two photons. 

Read more about Quantum nonlinear optics

Experimental research in nanophotonics and quantum optics is tremendously costly. A thorough effort requires a certain critical mass both in terms of  state-of-the-art equipment and man-power.

We gratefully acknowledge financial support from the following sources:

• Danish National Research Foundation
• Novo Nordisk Foundation
• Innovationsfonden
• Horizon 2020
• The European Research Council
• Ministry of Higher Education and Science
• Villum Fonden
• Lundbeckfonden
• Carlsbergfondet
• Augustinusfonden
• A.P. Møller og Hustru Chastine Mc-Kinney Møllers Fond til almene Formaal

Når lys flettes på tværs af tid, kan der skabes simplere kvantecomputere

• Link to article in Sciencenews (2025)

Mærkværdigt kvanteprincip gør svære AI-beregninger muligt

• Link to article in Weekendavisen (2025) 

Chippen over dem alle
The chip over them all

• Link to article on Weekendavisen (2023)

Peter Lodahl interviewed: De skal løse de store problemer: Kvantecomputere trodser enhver logik
Peter Lodahl interviewed: They should solve all the big problems: The quantum computer defies all logic

• Link to article on Herning Folkeblad (2023)

Kvantestartup er klar med sin første revolutionerende chip
Quantum startup is ready with their first revolutionary chip. 

• Link to article on Børsen (2023)

Danske forskere krypterede samtale med kvanteteknologi og en hacker gik i fælden
Danish researchers encrypted conversation with quantum technology and a hacker got caught
Articles on the quantum encrypted channel between DTU and NBI.

• Link to article on DR.dk (2022)
• Link to article on Politiken (2022)
• Link to article on Børsen (2022)

Nyt firma vil masseproducere qubit til optisk kvantecomputer
New company will mass produce qubits for optical quantum computers

• Link to article from Ingeniøren (2021)

Kvantecomputeren - det nye rumkapløb
The quantum computer - the new space race

• Link to story on Danish national television DR.dk (2021)

Dansk chip kan danne grundlag for optiske kvantesimulatorer
Danish chip will form the foundation for optical quantum simulators

• Link to article from Ingeniøren (2020)

Kvante-gennembrud: Dansk opfindelse kan give computere superkræfter
Quantum breakthrough: Danish invention can give computers superpowers

• Link to article on Videnskab.dk (2020)

Megabevilling til kvantesimulatorer viser, at grundforskning lønner sig.
Large grant for quantumsimulators shows that fundamental research pays off.
Article (in Danish) on our new center Solid-state quantum simulators for biochemistry.

• Link to article on uniavisen.dk (2020).

"Den interne proces var ekstrem. Vild og blodig."
"The internal process was extreme. Wild and bloody."
Profile (in Danish) of recent recognitions and scientific accomplishments by Prof. Peter Lodahl and his Quantum Photonics research group.

• Link to article on uniavisen.dk (2017).

Danske forskere baner vejen for fremtidens computer.
Danish researchers pave the way for future computer.
Article (in Danish) on our recent effors towards implementing quantum technology.

• Link to article on information.dk (2017).

Building the Quantum Internet.
Interesting article on how a solid-state material based quantum internet could be realized:

• Link to Association for Computing Machinery (ACM) article (2017).

Chiral quantum optics, Nature (2017).
Highlighted in more than 25 news stories in scientific and general online magazine. Here are some examples:

• First Step Towards Photonic Quantum Network.
  
• Kvantenetværket der kender forskel på højre og venstre (further down the page).
  
• Development of Photonic Quantum Network

Deterministic photon-emitter coupling in chiral photonic circuits, Nature Nanotechnology (2015).

• Quantum networks: Back and forth are not equal distances, Phys.org (July 2015).
• Physicists have forced light to move in one direction inside the chip, Ria.ru (July 2015).
• Kvantemekanisk gennembrud: Dansk chip kan styre lys-partikler, DR (July 2015).

Nonuniversal intensity correlations in a two-dimensional Anderson-localizing random medium, Physical Review Letters 109, 253902 (2012).

• The paths of photons are random - but coordinated (December 2012).
• How photons mutually coordinate their paths, Novus light Technologies (January 2013).
• Photons sense each other, Photonics.com (January 2013).
• Light Labyrinth, Optics&Photonics News (March 2013).

Optical cavity cooling of mechanical modes of a semiconductor nanomembrane, Nature Physics 8, 168-172 (2012).

• Heating cools a semiconductor, physicsworld.com, (January 2012).

Strongly Modified Plasmon-Matter Interaction with Mesoscopic Quantum Emitters, Nature Physics 7, 215-218 (2011).

• Enhanced Coupling of Mesoscopic Quantum Dots to Plasmons, 2Physics.com, (January 2011).

Quantum Interference and Entanglement Induced by Multiple Scattering of Light, Phys. Rev. Lett. 105, 090501 (2010).

• Kvantecomputeren får potens af danske fysikere, Videnskab.dk, (August 2010).

Cavity quantum electrodynamics with Anderson-localized modes, Science 327, 1352 (2010).

• Quantum Devices to Thrive on Disorder, Optics & Photonics focus, (March 2011).
• Uperfekte chips kan bane vejen for ny kvanteteknologi, Aktuel Naturvidenskab nr. 6, 2010.
• For quantum computer, add a dash of disorder, ScienceNews, (March 2010).
• Shoddy construction beats precision in quantum world, NewScientist, (March. 2010).
• Imperfect Chips Enhance Quantum Technology, photonics.com, (March 2010).
• Quantum Computing Thrives on Chaos, Wired Science, (March 2010).
• Imperfections are perfect, Alpha Galileo, (March 2010).
• DTU-forskere: Uorden er vejen til chips i kvantecomputere (in Danish), Ingeniøren, (March 2010). 

Observation of Spatial Quantum Correlations Induced by Multiple Scattering of Nonclassical Light, Phys. Rev. Lett. 102, 193901 (2009).

• Tåget kvantefysik giver lys idé (in Danish), videnskab.dk, (Dec. 2009).

Podcast

• "Quantum Dot, Quantum Computer" with Peter Lodahl, by Photonics Spectra (2023)

• ”Fremtiden starter i Niels Bohrs kælder”, with Peter Lodahl, by Techtopia 291, IDA, (2023)

• “Hackernes værste mareridt”, with Peter Lodahl, by 49 Indium (2023)

•  "Lyset" with Peter Lodahl, by Christiansen & Andersen, (2017)

Selected popular papers

C. Faurby & P. Lodahl. En kvantekomputer baseret på lys. KVANT, p. 14-17 (2023).

A.Sørensen, P. Lodahl, and K. Splittorff. På tærsklen til en ny kvanteteknologisk revolution. KVANT (2021).

P. Lodahl, At kontrollere udsendelsen af lys (in Danish), Aktuel Naturvidenskab 4, 15-17 (2004).

P. Lodahl and W. L. Vos, Controlling spontaneous emission with photonic crystals, Photonics Spectra 39 (3): 64+ MAR (2005).

P. Lodahl, Lys i fotoniske krystaller og optiske nanobokse (in Danish), Naturens Verden 1, p. 29-35 (2006).

P.T. Kristensen, P. Lodahl, and J. Mørk, To decay or not to decay – or both! Quantum mechanics of spontaneous emission, DOPS Nyt 1, p. 4-8 (2008).

We currently have a number of vacancies in the Quantum Photonics Group (PhD, postdoc, assistant professor). Please contact Peter Lodahl:lodahl@nbi.ku.dk.

We are continuously looking for enthusiastic and talented students. If you are interested in learning more about an exciting B.Sc./M.Sc. project, please contact Peter Lodahl (lodahl@nbi.ku.dk), or see our Master projects description page.

External grants

A number of external grant possibilities exist for joining the Quantum Photonics Group at the Niels Bohr Institute. If you are interested in applying, contact Prof. Peter Lodahl well ahead of the application deadline.

Marie Skłodowska-Curie Actions

The Marie Skłodowska-Curie actions support researchers at all stages of their careers.

The Carlsberg Foundation

Postdoctoral grants for outstanding PhDs to establish independent research activities in Denmark.

The Villum Foundation

5 years funding within Young Investigator Programme.

European Research Council (ERC)

5 years ERC Starting Grant for talented researchers with 2-12 years research experience after the PhD.'

Sapere Aude

Up to 4 years funding for talented researchers within 8 years research experience after the PhD.