FTP project – University of Copenhagen

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Quantum Photonics > Funding > FTP project

FTP project

FTP grant: Nanophotonic single-photon sources for quantum information technology 

The Quantum Photonics Group has from January 2008 received a grant from the Danish Agency for Science Technology and Innovation (Forskningsrådet for Teknologi og Produktion, grant 274-07-0459). In this project two novel technologies will be explored to develop nanophotonic single-photon sources based on either photonic crystal waveguides or plasmon nanowires. The project will run for three year. Currently we have vacancies for postdoc positions within this project, for more information, contact Peter Lodahl: pel@com.dtu.dk

Project goals

The aim of the project is to construct all-solid-state nanophotonic devices for use in scalable quantum communication systems. Quantum information allows fundamentally new, secure, and efficient ways of processing information. One major challenge is to construct an efficient optical device that emits one single photon at a time. With such a single-photon source unbreakable secret codes can be communicated through quantum cryptography, and it provides a vital ingredient in quantum computing schemes. An efficient and reliable single-photon source can be constructed by coupling an emitter to one optical mode. We will pursue two novel routes that employ tailored nanophotonic materials for enhancing the coherent coupling between light (one photon in a waveguide mode) and matter (one quantum dot).

The envisioned novel devices are depicted in the figure below. The first scheme (left plot), utilizes a single quantum dot in a photonic crystal waveguide. In a photonic crystal waveguide, light dispersion can be tailored whereby photons are significantly slowed down. This also implies that light-matter interaction is enhanced such that single photons will be coupled efficiently and fast from the quantum dot to the waveguide, yielding an efficient single-photon source with a high bit-rate. In the second approach (right plot) the excitation of a quantum dot is transferred to a surface plasmon that is guided in a metal nanowire. With this technique, the quantum dot excitation is harvested with very high efficiency. Subsequently the surface plasmon can be coupled out as a single photon by evanescent coupling of the nanowire to an optical waveguide.

Left: Photonic crystal membrane waveguide with an emitting quantum dot (red dot) in side-view (upper image) and top-view (lower image). An excited quantum dot emits one photon at a time, which is directed into the waveguide with very high efficiency. Right: A quantum dot (green dipole) is optically excited (large arrow) and decays into the surface plasmon mode of the nanowire (gray wire). The plasmon is coupled to a nearby waveguide (dark blue waveguide) whereby a single photon can be coupled out in a well-defined direction (small arrow).

Popular description of research project (in Danish)

I klassisk fysik beskrives lys som en bølge. I begyndelsen af det 20 århundrede opdagede man at lys er kvantiseret, dvs. det er opbygget af små bølgepakker, der i mange situationer opfører sig som partikler. Disse fotoner udgør den fundamentalt mindste bestanddel af lys. De lyskilder, man anvender i hverdagen, udsender sædvanligvis mange milliarder fotoner, og i dette tilfælde kan lysets opførsel beskrives ved den klassiske fysik.  Imidlertid er det muligt at fremstille lyskilder, der udsender netop én foton ad gangen. Sådanne en-foton lyskilder vil blive bygget i dette projekt. En-foton lyskilder er beskrevet ved kvantemekanikkens love og opfører sig fundamentalt anderledes end klassiske lyskilder. Dette kan bl.a. udnyttes til at kommunikere via ubrydelige koder (kvantekryptografi) eller på længere sigt til at bygge en kvantecomputer, der kan udføre visse beregninger langt mere effektivt end en klassisk computer. Vi vil benytte halvleder teknologien til at fremstille en-foton kilder, der er fundamentalt anderledes end eksisterende en-foton kilder, og som vil være langt mere effektive. Vi bruger såkaldte kvantepunkter som en-foton lyskilder, der kan opfattes som halvleder "design atomer", hvor energien af de elektroniske overgange i kvantepunktet kan kontrolleres. Ved at nano-strukturere materialet som omgiver kvantepunktet er det muligt at øge effektiviteten af en-foton lyskilden betydeligt, da fotonen kan kobles effektivt til en ønsket "mode" i en optisk bølgeleder. Vi vil udnytte denne teknik til at fremstille en-foton kilder, hvor med op til 95% sandsynlighed én elektron i et kvantepunkt omsættes  til én foton i en optisk bølgeleder.

Dissemination

The outcome of our research is published in international journals. For a list of recent publications, see here

Popular papers about our research and information about relevant courses at KU can be found here.