A semiconductor source of triggered entangled photon pairs

Toshiba Research Europe Limited, 260 Cambridge Science Park, Cambridge CB4 0WE, UK.
Nature (Impact Factor: 41.46). 02/2006; 439(7073):179-82. DOI: 10.1038/nature04446
Source: PubMed


Entangled photon pairs are an important resource in quantum optics, and are essential for quantum information applications such as quantum key distribution and controlled quantum logic operations. The radiative decay of biexcitons-that is, states consisting of two bound electron-hole pairs-in a quantum dot has been proposed as a source of triggered polarization-entangled photon pairs. To date, however, experiments have indicated that a splitting of the intermediate exciton energy yields only classically correlated emission. Here we demonstrate triggered photon pair emission from single quantum dots suggestive of polarization entanglement. We achieve this by tuning the splitting to zero, through either application of an in-plane magnetic field or careful control of growth conditions. Entangled photon pairs generated 'on demand' have significant fundamental advantages over other schemes, which can suffer from multiple pair emission, or require post-selection techniques or the use of photon-number discriminating detectors. Furthermore, control over the pair generation time is essential for scaling many quantum information schemes beyond a few gates. Our results suggest that a triggered entangled photon pair source could be implemented by a simple semiconductor light-emitting diode.

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Available from: R. Mark Stevenson, Oct 04, 2015
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    • "Moreover, although superconductivity can enhance emission rates, it is not necessary for the generation of entanglement in isolated emitters such as QDs where discrete levels allow entanglement generation without superconductivity. [11] [12] Two-dimensional and bulk semiconductor structures, at the core of the existing semiconductor optoelectronic infrastructure, are significantly simpler and more efficient, and they have been shown lately to result in enhanced electrically-driven light emission when combined with superconductors [21] [22] [23]. In contrast to QD-based sources, however, the continuum of states in these structures allows population of infinitesimally close states by electrons with the same spin – preventing any polarization correlation between the emitted photons without superconductivity. "
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    ABSTRACT: We propose a novel approach for efficient generation of entangled photons, based on Cooper-pair luminescence in semiconductors, which does not require isolated emitters such as single atoms or quantum dots. We show that in bulk materials, electron-spin entanglement in Cooper pairs should not be expected to be translated into pure entangled photons despite the selection rules, due to mixing introduced by light-hole heavy-hole degeneracy. Semiconductor quantum wells, however, remove this degeneracy, allowing efficient photon entanglement generation in simple electrically-driven structures, taking advantage of the superconducting macroscopic coherence. The second-order decay of two-electron states in Cooper-pair luminescence leaves no which-path information, resulting in perfect coherence between two pathways and hence in principle, perfect entanglement. We calculate the purity of the entangled-photon state and find that it increases for larger light-hole heavy-hole energy splitting and for lower temperatures. These results provide new insights into light-matter interaction in solids and enable realization of novel quantum photonics based on matter condensates.
    Physical Review B 03/2014; 89:094508. DOI:10.1103/PhysRevB.89.094508 · 3.74 Impact Factor
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    • "The unconverted QD material is called wetting layer [2]. Semiconductor QDs are potentially ideal for achieving large arrays of reproducible entangled photon generators as they allow the generation of requested photons [3] [4] with no dependence to probabilistic processes [5]. Recently, in state of the art treatise it is reported that QDs arrays can be employed to obtain areas with up to 15% polarization entangled photon emitter along with fidelities as high as 0.721 ± 0.043 [6]. "
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    ABSTRACT: In this study we have performed a numerical approach to investigate the optical properties of GaN/AlN quantum dots (QDs. We have used nice homemade finite element method (FEM) codes to solve the Schrödinger equation, in presence and absence of wetting layer. The optical properties of both well-known, truncated pyramids–shaped, wurtize (WZ) and zinc blande (ZB) QDs have been investigated. It is demonstrated, there is slight amount of difference between all orders of absorption coefficients and relative refractive index changes (RRIC) for both structures. The effect of relaxation rate studied as well. Overlay it is shown that the optical properties ZB/WZ QDs could be engineered in well-manner.
    Journal of the European Optical Society Rapid Publications 01/2014; 9. DOI:10.2971/jeos.2014.14011 · 1.23 Impact Factor
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    • "Moreover, the photon with the narrow band have a long coherence time, the tolerance of the fiber length fluctuations and chromatic dispersion could be increased if it transmits in the fiber as the information carrier. Spontaneously parametric down-conversion (SPDC) [6] in nonlinear crystals is demonstrated more practically with respect to other techniques, such as Raman scattering or spontaneously four-wave mixing in atomic ensembles [7] [8] [9] [10] [11], and bi-exiton cascade in quantum dot [12] [13]. However, due to the broad spectra of SPDC source (of the order of THz), the bandwidth needs to be reduced significantly. "
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    ABSTRACT: In this paper, we present a narrow bandwidth source at the telecom wavelength based on type II PPKTP crystal inside an optical cavity. Simultaneous resonances of the pump and the two down-converted fields are achieved by special design of the cavity. This is a triple resonances optical parametric oscillator (OPO) far below threshold, which generates photon pairs at around 1560 nm with a bandwidth of 8 MHz. A coherence time of 27.7 ns is estimate by a time correlation measurement, and the estimated photon pairs generating rate is 134 s-1MHz-1mW-1. As entangled photon pairs in the telecom regime is suitable for long distance transmission and manipulation, this source is desirable for the demands of quantum communication.
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