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Advances in Optical Sciences Congress

Entangled Photon Pair Sources Fabricated from InAs Quantum Dots

D. A. Ritchie, R. M. Stevenson, Robert James Young, A J Hudson, D J P Ellis, Anthony J. Bennett, P. Atkinson, K Cooper, Christine A. Nicoll, Andrew J. Shields

Published Jan 1, 2009• 0 citations
Publisher

Abstract

We have fabricated and optimized triggered sources of entangled photon pairs using self-assembled InAs quantum dots. After optimization, a fidelity to the ideal entangled state of over 90% has been achieved.
DOI
10.1364/ipnra.2009.ime4

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The quick development of quantum technologies and quantum communication demands a continuous search for more efficient and with higher performance quantum sources and devices. In particular, quantum dots are firmly established sources of single photon emitters and entangled photon pairs, with entanglement of photons emitted by a single quantum dot probed in polarization[1], time-bin[2] and hyperentanglement[3]. Although spontaneous parametric down conversion sources (SPDC) are widely used as entangled photon sources with the highest values of entanglement[4], are being reached by quantum dot devices[5]. With similar quality as SPDC sources, QDs however stand out as sources with sub-Poissonian statistics, essential for safe quantum communication. Still, most of the quantum dots devices exhibit low extraction efficiencies. Attempts to maximize the extraction efficiency involve sophisticated engineered photonic systems[6,7]. Furthermore, the accurate alignment of the quantum dot-cavity system is crucial for an effective quantum dotcavity coupling and hence an emission enhancement into free space[8]. All of this implies the need of intricated nanofabrication processes. Here we present a simple, scalable photonic device that grants efficient creation of entangled photon pairs from InAs quantum dots. The device, spontaneously formed during the growth process, is based on pairs of bottom/top distributed bragg reflectors (DBRs). A propagating deformation in the DBRs, leads to the formation of self-aligned dimples on top of the QDs, resulting in a self-aligned quantum-dot cavity system[9]. Therefore, costly and complex deterministic nanofabrication techniques are not required. In this work, the device performance was characterized, showing experimental collection efficiencies of 0.17, with theoretically pair extraction efficiencies above 0.45. Furthermore, a Purcell enhancement up to 1.7 was obtained. Finally, the device potential to generate time-bin entangled photons was investigated performing state tomography measurements. The subsequent reconstruction of the density matrix yields a concurrence of 0.70(10) and a fidelity of 0.84(5).
The generation of entangled photon pairs is a fundamental cornerstone of quantum optics, and an essential technology in the high profile field of quantum communication and computing. Currently the most widely used techniques for generating entangled photon pairs are nonlinear optical processes, such as parametric down conversion, which produce a probabilistic number of pairs per excitation cycle. Such a source is of limited use in quantum information/processing applications where a regular stream of single entangled photon pairs is usually required. We have produced such a triggered source from a semiconductor device for the first time, using a two-photon cascade in a single quantum dots, demonstrating efficiencies up to 70%, close to the level required for useful applications. Single quantum dots could prove to be the first robust and compact triggered source of entangled photons.