Nika Akopian

Bio: Nika Akopian is an academic researcher from Technical University of Denmark. The author has contributed to research in topics: Quantum dot & Nanowire. The author has an hindex of 22, co-authored 63 publications receiving 2726 citations. Previous affiliations of Nika Akopian include Technion – Israel Institute of Technology & Kavli Institute of Nanoscience.

Entangled Photon Pairs from Semiconductor Quantum Dots

Abstract: Tomographic analysis demonstrates that the polarization state of pairs of photons emitted from a biexciton decay cascade becomes entangled when spectral filtering is applied. The measured density matrix of the photon pair satisfies the Peres criterion for entanglement by more than 3 standard deviations of the experimental uncertainty and violates Bell's inequality. We show that the spectral filtering erases the "which path" information contained in the photons' color and that the remanent information in the quantum dot degrees of freedom is negligible.

Bright single-photon sources in bottom-up tailored nanowires.

Abstract: The ability to achieve near-unity light-extraction efficiency is necessary for a truly deterministic single-photon source. The most promising method to reach such high efficiencies is based on embedding single-photon emitters in tapered photonic waveguides defined by top-down etching techniques. However, light-extraction efficiencies in current top-down approaches are limited by fabrication imperfections and etching-induced defects. The efficiency is further tempered by randomly positioned off-axis quantum emitters. Here we present perfectly positioned single quantum dots on the axis of a tailored nanowire waveguide using bottom-up growth. In comparison to quantum dots in nanowires without waveguides, we demonstrate a 24-fold enhancement in the single-photon flux, corresponding to a light-extraction efficiency of 42%. Such high efficiencies in one-dimensional nanowires are promising to transfer quantum information over large distances between remote stationary qubits using flying qubits within the same nanowire p-n junction.

Crystal Phase Quantum Dots

Abstract: In semiconducting nanowires, both zinc blende and wurtzite 1 crystal structures can coexist. 2-4 The band structure difference between the two structures can lead to charge confinement. 5 Here we fabricate and study single quantum dot devices 6 defined solely by crystal phase in a chemically homogeneous nanowire and observe single photon generation. More generally, our results show that this type of carrier confinement represents a novel degree of freedom in device design at the nanoscale.

Hybrid semiconductor-atomic interface: slowing down single photons from a quantum dot

Abstract: Combining semiconductor quantum dots and atomic systems allows the light emitted from a quantum dot to be temporarily stored. Here, scientists describe a hybrid semiconductor-atomic interface that can slow down a single photon emitted from a quantum dot by 15 times its temporal width. The findings are attractive for the implementation of quantum memories and quantum repeaters.

A light-hole exciton in a quantum dot

Abstract: An electron and a hole trapped in the same quantum dot couple together to form an exciton. Conventionally the hole involved is a heavy hole. Light-hole excitons are now observed by applying elastic stress to initially unstrained gallium arsenide-based dots. The quasiparticles are identified by their optical emission signature, and could be used in future quantum technologies.

Quantum entanglement

Abstract: All our former experience with application of quantum theory seems to say: {\it what is predicted by quantum formalism must occur in laboratory} But the essence of quantum formalism - entanglement, recognized by Einstein, Podolsky, Rosen and Schr\"odinger - waited over 70 years to enter to laboratories as a new resource as real as energy This holistic property of compound quantum systems, which involves nonclassical correlations between subsystems, is a potential for many quantum processes, including ``canonical'' ones: quantum cryptography, quantum teleportation and dense coding However, it appeared that this new resource is very complex and difficult to detect Being usually fragile to environment, it is robust against conceptual and mathematical tools, the task of which is to decipher its rich structure This article reviews basic aspects of entanglement including its characterization, detection, distillation and quantifying In particular, the authors discuss various manifestations of entanglement via Bell inequalities, entropic inequalities, entanglement witnesses, quantum cryptography and point out some interrelations They also discuss a basic role of entanglement in quantum communication within distant labs paradigm and stress some peculiarities such as irreversibility of entanglement manipulations including its extremal form - bound entanglement phenomenon A basic role of entanglement witnesses in detection of entanglement is emphasized

Solid-state single-photon emitters

Abstract: This Review summarizes recent progress of single-photon emitters based on defects in solids and highlights new research directions. The photophysical properties of single-photon emitters and efforts towards scalable system integration are also discussed.

Interfacing single photons and single quantum dots with photonic nanostructures

Abstract: Quantum dots embedded in photonics nanostructures provide unprecedented control over the interaction between light and matter. This review gives an overview of the theoretical principles involved, as well as applications ranging from high-precision quantum electrodynamics experiments to quantum-information processing.

Multiphoton entanglement and interferometry

Abstract: Multiphoton interference reveals strictly nonclassical phenomena. Its applications range from fundamental tests of quantum mechanics to photonic quantum information processing, where a significant fraction of key experiments achieved so far comes from multiphoton state manipulation. The progress, both theoretical and experimental, of this rapidly advancing research is reviewed. The emphasis is given to the creation of photonic entanglement of various forms, tests of the completeness of quantum mechanics (in particular, violations of local realism), quantum information protocols for quantum communication (e.g., quantum teleportation, entanglement purification, and quantum repeater), and quantum computation with linear optics. The scope of the review is limited to ``few-photon'' phenomena involving measurements of discrete observables.