Hy-Q consists of four research groups at the Niels Bohr Institute, University of Copenhagen.

1) The Quantum Photonics Group led by Prof. Peter Lodahl who is the Director of Hy-Q. Google Scholar.

2) The Theoretical Quantum Optics Group led by Prof. Anders Sørensen. Google Scholar.

3) The Quantum Optomechanics Group led by Prof. Albert Schliesser. Google Scholar.

4) The theoretical group led by Prof. Klaus Mølmer. Google Scholar.

Hy-Q is generously funded by a Center of Excellence grant from the Danish National Research Foundation.

Getting to the Center for Hybrid Quantum Networks

The Center for Hybrid Quantum Networks is located at the Niels Bohr Institute (Building T), University of Copenhagen (Blegdamsvej 17, 2100 Copenhagen).

Getting to Hy-Q

By Public Transportation

You are able to reach Hy-Q easily with both metro and bus. The Niels Bohr Institute is located a 5 minute walk from Trianglen metro station, where the metro M3 stops. This metro also stops at large stations such as Kgs Nytorv and Copenhagen Central Station. Tickets for the metro can be bought in the metro stations.

From Nørreport Station the institute is easily reachable with bus. Take bus no. 150S, 184, 185 or 15E from Nørreport St going north/west. Get off at Righshospitalet Syd (Tagensvej) (5 minutes). The Niels Bohr Institute (Blegdamsvej 17) is then a 5 minute walk from here. Tickets can be bought at stations and in the bus with cash. Tickets can be used for both metro, train and bus. 

Traveling from the Central Station

The Center for Hybrid Quantum Networks (Hy-Q) exploits photons to merge disparate quantum system into large scale quantum networks. The long-term perspective of the research is to enable large scale processing of quantum information over global distances.

Quantum theory was founded more than a century ago and revolutionized our conception of the world through highly counterintuitive phenomena such as quantum superposition and entanglement.

Today a second revolution is taking place based on the ability to fully control quantum phenomena in modern experiments. The outstanding challenge is to scale small quantum systems into large and complex architectures. Such quantum networks open a whole new horizon by creating quantum objects that have never existed in nature before.

The unsolved fundamental question is: how large and complex can we make a quantum system before the quantum character is lost and it is described by classical physics? Addressing this question could ultimately lead to a quantum internet, connecting the world by quantum entanglement.

Such long-term transformative technology may offer solutions to large societal challenges within energy, security, and supercomputing. 

Within the Center of Excellence “Hybrid Quantum Networks” (Hy-Q) we pursue a hybrid approach towards the quantum internet. Realizing that the various technology platforms have pros and cons the emphasis is on merging different quantum systems in a “best-of-all-worlds” approach.

Hy-Q exploits and merges three different quantum platforms, photons, emitters and phonons, to enable remote quantum connection, manipulation and storage of quantum information.

PhD Theses by Hy-Q

2024

2023

• "Quantum: Illuminated - Theory of light-matter interaction for quantum enhanced technologies" by O. A. Sandberg. Link to thesis. 
  
  
• "Single-photon sources as a key resource for developing a global quantum network" by E. M. Ruiz. Link to thesis.
  
  
• "Topological Waveguides and Symmetrical Droplet Quantum Dots for Scalable Photonic Quantum Technology" by N. V. Hauff. Link to thesis. 
  
  
• "Optomechanical Memory for Light" by M. B. Kristensen. Link to thesis.
  
  
• "Electro- and opto-mechanics with soft-clamped membrane resonators at milliKelvin temperatures for quantum memory and transduction" by E. Planz. Link to thesis.
  
  
• "Heterogeneous integration of GaAs waveguides on low loss substrates for quantum photonic circuits" by A. Shadmani. Link to thesis.
  
  
• "Spin-Photon Interface for Quantum Information Processing" by M. Lai. Link to thesis.

• "Photonic circuits with multiple quantum dots" by C. Papon. Link to thesis.

2022

• "Nonlinear Phenomena in Dissipation Diluted Nanomechanical Resonators" by L. Catalini. Link to thesis.

2021

• "Novel nanofabrication methods and processes for antum photonic integrated circuits" by Y. Wang. Link to thesis.
• "A Quantum Dot Source of Time-Bin Multi-Photon Entanglement" by M. H. Appel. Link to thesis.
• "Novel Optical Polymer-Based Interfaces to Quantum Photonic Integrated Circuits" by A. D. Ugurlu. Link to thesis.
• "Optomechanics at the room temperature - Towards classical and quantum applications" by S. Saarinen. Link to thesis.
• "Ultra-coherent electro-mechanics in the quantum regime" by Y. Sais. Link to thesis.

2020

• "Deterministic Single and Multi-Photon Sources with Quantum dots in Planar Nanostructure" by F. T. Pedersen. Link to thesis.
• "Optical spin-mechanics quantum interface: entanglement and back-action evasion" by R. Thomas. Link to thesis.
• "Quantum Correlations Generated by a Soft-Clamped Membrane-in-the-Middle System" by J. Chen. Link to thesis.
• "Quantum Measurement and control of a mechanical resonator" by M. Rossi. Link to thesis.

2019

• "Multiphoton generation from a single quantum dot in a photonic nanostructure" by T. Hummel. Link to thesis.
• "Deterministic quantum photonic devices based on self-assembled quantum dots" by T. Pregnolato. Link to thesis.
• "Sensitive electro-optical transduction through resonant electro- and optomechanics" by A. Simonsen. Link to thesis.

2018

• "Quantum Information Processing with Quantum Optical Systems" by V. E. Elfving. Link to thesis.
• "Looking for mechanical hiccups & High dimensional mdi–QKD" by L. Dellantonio. Link to thesis.

Master projects 2023

Rasmus Bruhn Nielsen

Master's project: Towards cluster state generation using charged quantum dot

Supervisor: Peter Lodahl, Alexey Tiranov

Master projects 2022

Camilla Birch Okkels

Master's project: Theoretical optimizations of quantum repeaters based on atomic ensembles

Supervisor: Anders Søndberg Sørensen

Nicolas Remy Høegh Pedersen

Master's Thesis: Nano-Opto-Mechanical Systems for photon control

Supervisor: Leonardo Midolo

Love Alexander Mandla Pettersson

Master's Thesis: Exploring near-term quantum applications with graph states from quantum emitters

Supervisors: Peter Lodahl, Stefano Paesani

Jonas Højsted Dalgaard

Master's project: Violating Bell's inequality with continuous variables & qubit-cavity interaction

Supervisor: Anders Søndberg Sørensen

Master projects 2021

Buyuan Luo

Master's project: Selection Rules of a simple model of a Quantum Dot

Supervisor: Anders Søndberg Sørensen

Sif Kristine Fugger

Master's Thesis: Design and characterization of nano-mechanical quantum photonic devices

Supervisors: Leonardo Midolo, Peter Lodahl

Laurits Høgel

Master thesis: Positioned InAs Quantum Dots from Selective Area Growth -  Manufacturing, Characterization and Optical Measurements

Supervisors: Peter Lodahl and Peter Krogstrup

Arianne Brooks

Master's Thesis: Whispering-gallery-modes in QD-embedded micro disc resonators for optical routing

Supervisors: Nir Rotenberg, Leonardo Midolo and Peter Lodahl

Clara Celeste Qvotrup

Master's Thesis: Deflecting waveguides for three-dimensional quantum photonic integrated circuits

Supervisor: Leonardo Midolo

Miren Lamaison Vidarte

Master's project: Photonic Control-Phase gate based on emitters with chiral interactions

Supervisor: Anders Søndberg Sørensen

Mikkel Thorbjørn Mikkelsen

Master's Thesis: Multiphoton and heralded entanglement sources for applications in quantum cryptography

Supervisors: Peter Lodahl, Ravitej Uppu 

Iñigo Lara Izcue

Master's project: Towards percolation-based quantum computing with a photonic machine gun

Supervisor: Anders S. Sørensen

Carlos Fernando Duarte Faurby

Master's Thesis: Frequency conversion of single photons for long distance quantum communication

Supervisors: Leonardo Midolo, Xiaoyan Zhou, Beatrice da Lio

Adam Søsted Knorr

Master's Thesis: Spectroscopy of Advanced Integrated Nanophotonic Devices and Quantum Dots

Supervisors: Peter Lodahl, Ravitej Uppu 

Mathias Jakob Rønne Staunstrup

Master's Thesis: Measuring the quantum dot induced phase shift of light transmitted through a nanophotonic waveguide

Supervisors: Peter Lodahl, Hanna Le Jeannic, Nir Rotenberg

Simon Refshauge Pabst

Master's Thesis: Towards Spin-Multiphoton Entanglement from a Quantum Dot

Supervisors: Peter Lodahl, Alexey Tiranov

Collaborators

Hy-Q enjoys a range of highly active collaborations with world-leading research groups, which is witnessed by our publication list.

One particularly strong collaboration is with University of Basel (Prof. Richard Warburton) and University of Bochum (Profs. Andreas Wieck/Arne Ludwig). 

The Basel/Bochum/Copenhagen research teams are highly complementary bringing together expertise on ultra-high-quality quantum materials growth, semiconductor spin physics, and quantum optics, respectively.

Over the past 4 years, we have strongly consolidated this collaboration, which is implemented in the form of bi-weekly joint group meetings and a yearly 2-3 day get-together.

Additional active collaborations include Harvard, Cambridge, and ETH Zurich to highlight a few.

Start-up companies

The quantum photonics area is witnessing an increased interest from the private sector, and we are actively collaborating with several companies, e.g., within the Innovation Fund project FIRE-Q.

The start-up company Sparrow Quantum (launched in 2015) is a spin-out from our research team, is currently growing rapidly, and several joint projects with Hy-Q have been established.

We also collaborate with several other DNRF centers within the quantum area: with SPOC (DTU) we work on single-photon quantum key distribution and have demonstrated a field trial of our technology, as funded by Innovation Fund Denmark; with Qdev (NBI) we share nanofabrication facilities and work on molecular beam epitaxy quantum-materials growth; with CCQ (Aarhus University) we work on quantum nonlinear optics.

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 Hy-Q faculty and learn more.

Master Projects 2023

Quantum Photonics

Deterministic generation of entangled photons

Device-independent cryptography achieves unbreakable security by exploiting quantum correlations (e.g. entanglement) between the sender and the receiver. The practical implementation of such protocols requires efficient and high-fidelity entangled photon sources. Solid state emitters are the way forward for efficient quantum light generation due to the possibility to integrate them into a nanophotonic structure. Recent demonstrations of high-fidelity (> 97%) polarization entanglement using the biexciton cascade in GaAs/AlGaAs quantum dots open exciting route for deterministic entanglement generation. The project will deal with several aspects of the nanophotonic interfacing of these quantum dots including: 1) Efficient preparation of the quantum dot, 2) Extraction of entangled photon pairs and state tomography, 3) Sources of noise limiting the entanglement fidelity, 4) near-future applications of the entangled photons for cryptography. 

For more information, contact Prof. Peter Lodahl (lodahl@nbi.ku.dk).

Coherent single photons: Interfacing with memories

The distribution of quantum states across nodes in a quantum network is the key requirement for secure communication and distributed computing. A typical quantum network will involve interfacing disparate qubits (matter, photon, spin, etc.) to ensure maximum efficiency. Photons are robust carriers of information and hence are critical for interconnection. The disparity between the frequency and bandwidth across the qubits pose challenges in the interconnection. Efficiently crafting the bandwidth of the photon is the key enabler for photonic interconnects. Quantum dot single photon sources typically generate photons with GHz bandwidth. Efficient interfacing of photons with quantum memories (holding time ~ 0.1 – 1 us) requires ~10 MHz bandwidth. A promising way forward to achieve such coherent single photons is through Raman processes in a Λ system. The project will deal with coherent photon generation using one of the Λ-systems of a trion in a InAs quantum dot.  Key aspects: 1) Branching ratio and limits on the bandwidth of photons, 2) Generation and characterization  3) Pulse shaping for bandwidth manipulation. 

For more information, contact Prof. Peter Lodahl (lodahl@nbi.ku.dk).

Nonlinear chiral quantum optics

Chiral quantum light-matter interactions are a recently discovered consequence of using nanophotonic platforms for quantum optical experiments.  In chiral scenarios, the light-matter interaction is strongly directional, meaning that the interaction of photons with a quantum dot strongly depends on which way they travel, allowing for the design of novel and non-reciprocal quantum devices. Within this project, we will explore the nonlinearity of such chiral quantum interactions, using a blend of numerical modelling and optical experiments. 

For more information, contact Prof. Peter Lodahl (lodahl@nbi.ku.dk).

Giant cooperativity in planar structures

Cooperativity is a fundamental property within quantum optics that captures the strength of the coupling between light (photons) and matter (quantum emitters).  Within this project, we wish to enhance this cooperativity using resonant, planar nanophotonic structures, thereby setting the stage for the creation of efficient and complex quantum architecture. 

For more information, contact Prof. Peter Lodahl (lodahl@nbi.ku.dk).

Multicolour quantum optics

Quantum emitters such as quantum dots are inherently nonlinear at the ultimate, low-energy limit; after all, they can only absorb a single photon at a time.  This inherently large nonlinearity means that the interaction of a single emitter with a single photon can be significantly tuned by a single, control photon.  Within this project, we will model this multicolour nonlinear interaction and search for signatures of our model in optical experiments. 

For more information, contact Prof. Peter Lodahl (lodahl@nbi.ku.dk).

Topological quantum photonics

Topological photonic edge states, which exist at the interface between especially engineered photonic crystals, have recently been shown to guide photons emitted by a single quantum dot.  This has generated considerable excitement within the quantum photonics community as these edge modes are protected from backscattering due to defects or fabrication imperfections and, additionally, allow for directional and non-reciprocal light-matter interactions.  Within this project, we will study quantum light-matter interactions with topological edge-states using numerical modelling techniques. 

For more information, contact Prof. Peter Lodahl (lodahl@nbi.ku.dk).

Scalable chip-to-fiber coupling

The project aims at building an off-chip fiber delay based on optical fibers. Off-chip fiber delays are key ingredients for performing advanced quantum protocols and emitter de-multiplexing. Based on our state-of-the-art chip-to-fiber couplers, we are planning to couple multiple fibers to nanophotonic waveguides using matrix arrays. The project involves building/adapting a room-temperature setup for aligning and bonding chips to matrix arrays, perform numerical simulations of the optimal power transfer to fibers, design and (optionally) fabricate the chip and measure it in the lab. 

For more information, contact Asst. Prof. Leonardo Midolo (midolo@nbi.ku.dk).

Resonance fluorescence and Purcell enhancement

The goal is to design a device that enables a scheme for resonantly driving an emitter inside a cavity. There are different strategies that involve combining a tunable cavity and a waveguide-based resonant excitation scheme. The project involves numerical simulations of the device to improve the extinction between the pump laser and the emitted photons. The device is then characterized in the lab. Optionally, the student has the possibility to get training to the cleanroom and fabricate the sample. 

For more information, contact Asst. Prof. Leonardo Midolo (midolo@nbi.ku.dk).

Electro-optical routing of single-photons

Design a waveguide-based electro-optic switch operating at >10 MHz for fast optical routing of photons. The router is key to implement protocols for de-multiplexing single-photons. Based on our recent results in electro-optic routing technology, we plan to build an integrated Mach-Zehnder interferometer with embedded phase shifters. The project involves the design, fabrication, and characterization of the device. An interest in acquiring nanofabrication skills is preferred.  

For more information, contact Asst. Prof. Leonardo Midolo (midolo@nbi.ku.dk).

Quantum science has been gaining significant attention in recent years and substantial investments have been launched worldwide to further develop and scale-up this potentially disruptive technology area. Likewise, the public interest in quantum science and technology is growing.

Since Hy-Q is recognized internationally as a leading quantum-science center, we have been hosting numerous visits to our labs, e.g., politicians, investors, and other stakeholders in the quantum area.

Moreover, Hy-Q has participated in several press outreach activities, including podcasts, social media posts, television broadcasts etc.

Television

The Center for Hybrid Quantum Networks (Hy-Q) is located at the Niels Bohr Institute at Blegdamsvej 17, 2100 København.

	Peter Lodahl, Professor and Director of Hy-Q Blegdamsvej 17, 2100 København Ø, Office: 12-1-TB5 Email: lodahl@nbi.ku.dk Phone: +45 353-25306
	Anders Søndberg Sørensen, Professor and Deputy Director Blegdamsvej 17, 2100 København Ø, Office: 12-0-TA1a Email: anders.sorensen@nbi.ku.dk Phone: +45 353-25240 Mobile: +45 24 66 13 77
	Albert Schliesser, Professor Blegdamsvej 17, 2100 København Ø, Office: 12-1-TB3 Email: albert.schliesser@nbi.ku.dk Phone: +45 353-25401
	Klaus Mølmer, Professor Blegdamsvej 17, 2100 København Ø, Office: 12-0-TA3b Email: klaus.molmer@nbi.ku.dk
	Leonardo Midolo, Associate Professor Blegdamsvej 17, 2100 København Ø, Office: 12-1-TB6 Email: midolo@nbi.ku.dk Phone: +45 23 23 41 69
	Frederik Uldall, Senior Consultant Blegdamsvej 17, 2100 København Ø, Office: 12-1-TB8 E-mail: frederik.uldall@nbi.ku.dk Phone: +45 353-22414
	Dorte Christiane Garde Nielsen, Research Secretary Blegdamsvej 17, 2100 København Ø, Office: 12-1-TB7 E-mail: Dorte.Garde.nielsen@nbi.ku.dk Phone: +45 353-30180