– University of Copenhagen

Quantum Photonics > Research

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.

Scalable quantum photonic devices

12 November 2018

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).

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Quantum information processes with coherent single-photon sources

12 November 2018

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).

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Nanofabrication

12 November 2018

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.

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Controlling quantum light-matter interaction in photonic nanostructures

12 November 2018

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.

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Multiphoton entanglement using quantum dot spins

12 November 2018

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

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Quantum nonlinear optics

12 November 2018

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. 

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