Stevenson, R. M. et al. A semiconductor source of triggered entangled photon pairs. Nature 439, 179-182

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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    • "These properties provide them with potential applications in a wide variety of devices. For example, QDs have a great potential as building blocks for quantum information technologies , where single photon and entangled photon pair emissions from individual semiconductor QDs have been demonstrated [1] [2]. "
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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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    • "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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