Quantum Optics
Slowing down single photons from quantum dotsNowadays, the vast majority of information is transferred by light in optical fibers. The single elementary particle of light is called a photon. The advantage of single photons is that they can carry and transfer quantum information over very long distances, enabling 100% secure communication, impossible to crack. We have successfully designed a new type of semiconductor material (quantum dots), which emit photons at a frequency that can be combined with rubidium atoms. By guiding the emitted light through the atoms the speed of the photons is reduced to less than 4% of the speed of light in vacuum. The breakthrough can enable the realization of quantum memories - an essential component in quantum information technology. Merging semiconductor and atomic physics in a hybrid interface opens the way to a series of novel experiments and research directions. For instance, quantum memories and quantum repeaters for quantum dot generated photons can now be fabricated. This work was carried out in close collaboration with the Kavli Institute of Nanoscience at Delft University of Technology in the Netherlands.N. Akopian et al., Nature Photonics 5, 230 (2011) URL PDF This work was highlighted in: Nature Photonics, 5, 197 (2011) (March 31, 2011) URL PDF pro-physik.de (March 28, 2011) URL |
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Towards tunable indistinguishable photons from distant quantum dotsIn this work, we present steps towards the realization of quantum interference between two photons emitted from two independent QDs. The exciton energies of two nearby GaAs QDs located into spatially separated cavities are brought into resonance and overlapped at a beam splitter. Despite the fact that the short dephasing time of the selected QDs prevents us to observe quantum interference between the two photons, the approach could be applied to other QDs emitting transform-limited single photons.M. Benyoucef et al., Applied Physics Letters 95, 261908 (2009) URL PDF This work was highlighted in: Nature Materials 9, 94 (2010) URL PDF |
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First single photon source on silicon substrateSingle quantum emitters have become an emerging area of fundamental research during the last years, driven by the need for nonclassical light sources delivering single-photons on demand for future implementation in the field of quantum information processing. In this work, we demonstrate for the first time triggered single-photon emission from a single quantum dot grown on Si substrate. Our findings show that it is feasible to fabricate high quality indistinguishable single-photon sources aiming at compatibiltiy with Silicon ultra large scale integration technologies.M. Benyoucef et al., Nano Letters 9, 304 (2009) DOI: 10.1021/nl802948a (2008) URL PDF
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Strongly coupled semiconductor microcavitiesCoupled optical microcavities are attracting much interest for applications in integrated photonic circuits and for solid-state quantum electrodynamics. Arranging microcavities into photonic molecules (PMs) could offer new functionalities of devices. We fabricate PMs consisting of closely-spaced microdisks containing self-assembled quantum dots as emitters. A focused laser beam is used both as optical excitation and local heat source to obtain strong coupling of whispering gallery modes in PM by continuously tuning the refractive index of one of the disks which was confirmed by finite-difference time-domain simulations.M. Benyoucef et al., Physical Review B 77, 035108 (2008) URL PDF |
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Entangled photons from single quantum dotsSources of entangled photon pairs “on demand” are highly desirable in the field of quantum information and communication. The two photons produced by the biexciton-exciton (XX-X) cascade in a single quantum dot (see figure) may be used as polarization-entangled photon pairs. However, asymmetries in the quantum dot confining potential lift the degeneracy of the single exciton level (DEFS>0) and lead to the creation of classically (not quantum) correlated photon pairs. We have succeeded in the fabrication of high quality InAs/GaAs quantum dots with degenerate exciton recombination and shown that quantum correlated photon pairs can be produced at temperatures as high as 30 K.R. Hafenbrak et al., New Journal of Physics 9, 315 (2007) URL PDF |
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