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PUBLISHED ONLINE: 31 OCTOBER 2016 | http://dx.doi.org/10.1038/nphoton.2016.203
Web End =DOI: 10.1038/NPHOTON.2016.203
Scalability and foundry compatibility (as apply to conventional silicon-based integrated computer processors, for example) in developing quantum technologies are major challenges facing current research. Here we introduce a quantum photonic technology that has the potential to enable the large-scale fabrication of semiconductor-based, site-controlled, scalable arrays of electrically driven sources of polarization-entangled photons that may be able to encode quantum information. The design of the sources is based on quantum dots grown in micrometre-sized pyramidal recesses along the crystallographic direction (111)B, which theoretically ensures high symmetry of the quantum dotsa requirement for bright entangled-photon emission. A selective electric injection scheme in these non-planar structures allows a high density of light-emitting diodes to be obtained, with some producing entangled photon pairs that also violate Bells inequality. Compatibility with semiconductor fabrication technology, good reproducibility and lithographic position control make these devices attractive candidates for integrated photonic circuits for quantum information processing.
To develop quantum technologies, the scientic community is looking into several alternative practical routes such as super-conducting qubits, atoms on-chips and photonic integrated
circuits, among others14. All of the explored technologies have to solve the scalability and reproducibility problem if they are to deliver successful real-life applications. In the case of photonic quantum technologies, scalability requires moving from discrete optical elements to integrated photonic circuits and to on-chip solid-state sources, allowing, for example, thousands of units to operate in unisona requirement that is very hard to realize at the moment.
Semiconductor quantum dot (QD) technology is fundamentally compatible with modern fabrication/foundry processes, and on-demand identical, single and entangled photons have all been demonstrated by optical pumping514. Nevertheless, although the development of electrically pumped (EP) quantum light sources has advanced in general15, the development of a particular resource,EP entangled photon sources, has proven more challenging. After the rst report16, the community had to wait several years before a similar result could be obtained by other groups17. Importantly, the few devices reported so far utilized epitaxial self-assembledQD structures, that is, these devices had no control on the source location or on the number of sources in a single device (typically hundreds or more, and not just one or, in the best case scenario, a few): a critical...