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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

A solid state ultrabright source of entangled photon pairs

Adrien Dousse, J. Suffczyński, A. Beveratos, O. Krebs, Aristide Lemaître, Isabelle Sagnes, Jacqueline Bloch, Paul H. Voisin, P. Senellart

Published Dec 4, 2010• 1 citation
Publisher

Abstract

We demonstrate the fabrication of highly efficient sources of entangled photon pairs by inserting a semiconductor quantum dot in an optical cavity. Two electron-hole pairs trapped in a quantum dot (QD) radiatively recombine emitting a cascade of two polarization entangled photons. To extract both photons, we use a photonic molecule consisting of two identical micropillars, one empty, the other embedding a chosen QD. By adjusting the diameter of the pillars and their relative distance, we ensure that both optical transitions of the QD are simultaneously resonant to cavity modes. The emitted photon pairs are efficiently extracted thanks to Purcell effect. Doing so, we obtain the brightest sources of entangled photon pairs to date. We further show that the implementation of Purcell effect allows increasing the fidelity of the two photon state by reducing spin induced phase shift during the radiative cascade.

DOI
10.1117/12.871441

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We demonstrate the fabrication of highly efficient sources of entangled photon pairs by inserting a semiconductor
quantum dot in an optical cavity. Two electron-hole pairs trapped in a quantum dot (QD) radiatively recombine emitting
a cascade of two polarization entangled photons. To extract both photons, we use a photonic molecule consisting of two
identical micropillars, one empty, the other embedding a chosen QD. By adjusting the diameter of the pillars and their
relative distance, we ensure that both optical transitions of the QD are simultaneously resonant to cavity modes. The
emitted photon pairs are efficiently extracted thanks to Purcell effect. Doing so, we obtain the brightest sources of
entangled photon pairs to date. We further show that the implementation of Purcell effect allows increasing the fidelity
of the two photon state by reducing spin induced phase shift during the radiative cascade.
An outstanding goal in quantum optics and scalable photonic quantum technology is to develop a source that each time emits one and only one entangled photon pair with simultaneously high entanglement fidelity, extraction efficiency, and photon indistinguishability. By coherent two-photon excitation of a single InGaAs quantum dot coupled to a circular Bragg grating bull's-eye cavity with a broadband high Purcell factor of up to 11.3, we generate entangled photon pairs with a state fidelity of 0.90(1), pair generation rate of 0.59(1), pair extraction efficiency of 0.62(6), and photon indistinguishability of 0.90(1) simultaneously. Our work will open up many applications in high-efficiency multiphoton experiments and solid-state quantum repeaters.
In this work, we show that this drawback can be overcome by coupling an optical cavity in the form of a 'photonic molecule' to a single QD. Two coupled identical pillars are etched in a semiconductor planar microcavity, using an optical lithography method that ensures a deterministic coupling to the optical transitions of a pre-selected quantum dot. Acceleration of spontaneous emission ensures that most entangled photon pairs are emitted into two cavity modes, while improving the indistinguishability of the two optical recombination paths.
We introduce a scalable photonic platform that enables efficient generation of entangled photon pairs from a semiconductor quantum dot. Our system, which is based on a self-aligned quantum dot- micro-cavity structure, erases the need for complex steps of lithography and nanofabrication. We experimentally show collection efficiency of 0.17 combined with a Purcell enhancement of up to 1.7. We harness the potential of our device to generate photon pairs entangled in time bin, reaching a fidelity of 0.84(5) with the maximally entangled state. The achieved pair collection efficiency is 4 times larger than the state-of-the art for this application. The device, which theoretically supports pair extraction efficiencies of nearly 0.5 is a promising candidate for the implementation of bright sources of time-bin, polarization- and hyper entangled photon pairs in a straightforward manner.
Entangled photon pairs are a ubiquitous resource in quantum technologies, used in quantum key distribution and quantum networking as well as fundamental tests of non-locality. For scalable quantum networks, pairs that are indistinguishable in all unentangled degrees of freedom are essential, as they enable high-fidelity entanglement swapping across network nodes. To date the most-studied sources of "swappable" entangled photon pairs have been based on spontaneous parametric down-conversion (SPDC) in non-linear crystals. However, the probabilistic nature and unavoidable trade-off between brightness and unwanted multi-photon emission limits their performance in lossy channels. Here, we demonstrate a high-fidelity source of "swappable" entangled photon pairs using a semiconductor quantum dot (QD) coupled to a tunable microcavity. By actively modulating the QD emission between orthogonal polarisation states, delaying one path in a low-loss Herriott cell, and recombining the two on a balanced beam splitter, we generate entangled photon pairs with a fidelity of 96.1±0.596.1\pm0.596.1±0.5 %. We identify and mitigate fidelity-limiting factors, achieving a maximum fidelity of 98.1±0.598.1\pm0.598.1±0.5 % through time-resolved post-selection. The scheme suppresses residual multi-photon events concentrated near the excitation pulse and has only a modest impact on the rate. Furthermore, the photons are mutually indistinguishable, enabling efficient entanglement swapping. Our results establish semiconductor QDs as a viable platform for quantum network-compatible swappable entangled photon pair generation, with feasible entanglement generation rates exceeding 0.5 Gpairs/s.
We introduce a scalable photonic platform that enables efficient generation of entangled photon pairs from a semiconductor quantum dot. Our system, which is based on a self-aligned quantum dot- micro-cavity structure, erases the need for complex steps of lithography and nanofabrication. We experimentally show collection efficiency of 0.17 combined with a Purcell enhancement of up to 1.7. We harness the potential of our device to generate photon pairs entangled in time bin, reaching a fidelity of 0.84(5) with the maximally entangled state. The achieved pair collection efficiency is 4 times larger than the state-of-the art for this application. The device, which theoretically supports pair extraction efficiencies of nearly 0.5 is a promising candidate for the implementation of bright sources of time-bin, polarization- and hyper entangled photon pairs in a straightforward manner.
Summary form only given. The latest advances in the design and implementation of semiconductor sources of quantum light show their competence to efficiently deliver indistingishable single photons or photon pairs with high degree of entanglement. These achievements combined with the possibility of photon storage show the potential of quantum dots to become building blocks of a quantum network. Here we investigated the possibility to extend the use of micro-pillar cavities to extraction of photon pairs. Particularly, we are interested in quantum dots excited resonantly using a method of two-photon resonant excitation of the biexciton. We theoretically modelled the system consisting of a two-photon resonantly excited quantum dot placed in a micro-pillar cavity. We estimated the coupling strength required to achieve cavity mediated photon pair emission. We related this finding to the device design parameters, which indicate a feasible design. Controlling the parameters as cavity bandwidth and coupling strength we can achieve difference emission dynamics ranging from individual emission of biexciton and exciton photons to a cavity mediated bi-photon emission.