Brightest source of entangled photons
We have developed a broadband optical antenna for highly efficient extraction of entangled photons. With a yield of 37% per pulse, it is the brightest source of entangled photons reported so far. Our entangled photons are generated by the semiconductor material commonly used in optoelectronics, gallium arsenide, and therefore represents an important step towards exploring the potential of optical quantum technologies.
Y. Chen et al., Nature Commun. 9, 2994 (2018) URL
Scalable entangled photon sources for the long haul
Constructing a quantum network relies on transferring entangled states over long distances. This scenario can be implemented by “swapping” the entanglement between wavelength-matched entangled photon sources. Semiconductor quantum dots are a promising candidate for this task. Howeve, there is a longstanding challenge on scalability. With an on-chip PMN-PT/silicon MEMS device, we can tune the entangled photon emission from a quantum dot by more than 3000 times of the radiative linewidth without spoiling the entanglement. This work removes a major stumbling block to entanglement swapping with quantum dots.
The fastest entangled photon sources come from IIN
Triggered sources of entangled photon pairs are key components in most quantum communication protocols. Here we demonstrate strain-tunable entangled-light-emitting-diodes with entanglement fidelities as high as 0.83. Electrically driven at the highest speed ever (400 MHz), these entangled photon sources emerge as promising devices for high data-rate quantum applications. This work was carried out in close collaboration with the Johannes Kepler University Linz, Austria.
A wavelength-tunable single-photon emitting diode
The first all-electrically operated wavelength-tunable single-photon source is demonstrated. The device consists of an ultra-thin light-emitting diode containing self-assembled quantum dots integrated onto a piezoelectric crystal.Triggered single photons are generated via injection of short electrical pulses at operation speeds up to 0.8 GHz. The wavelength of the emitted single-photons can be tuned over a broad range by the strain field from the piezoelectric crystal.Our work provides exciting perspectives towards high data rate quantum communications relying on remote electrically-driven single-photon sources.
Making quantum dots electronically symmetric
The lack of structural symmetry which usually characterizes semiconductor quantum dots lifts the energetic degeneracy of the bright excitonic states and hampers severely their use as high-fidelity sources of entangled photons. We demonstrate experimentally and theoretically that it is always possible to restore the excitonic degeneracy by the simultaneous application of large strain and electric fields. This is achieved by using one external perturbation to align the polarization of the exciton emission along the axis of the second perturbation, which then erases completely the energy splitting of the states. This result, which holds for any quantum dot structure, highlights the potential of combining complementary external fields to create artificial atoms meeting the stringent requirements posed by scalable semiconductor-based quantum technology.
This work was chosen as PRL Editors' suggestion and selected for a Viewpoint in Physics (October 1, 2012) URL
Slowing down single photons from quantum dots
Nowadays, 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., Nat. Photonics 5, 230 (2011) URL PDF
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Towards tunable indistinguishable photons from distant quantum dots
In 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., Appl. Phys. Lett. 95, 261908 (2009) URL PDF
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Nature Materials 9, 94 (2010) URL PDF
First single photon source on silicon substrate
Single 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 Lett. 9, 304–307 (2009) URL PDF
Strongly coupled semiconductor microcavities
Coupled 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., Phys. Rev. B 77, 035108 (2008) URL PDF
Entangled photons from single quantum dots
Sources 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 J. Phys. 9, 315 (2007) URL PDF