Hybrid quantum dot-nanowire heterostructures for deterministic biphoton quantum communications

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Nontechnical description: Recently there has been intense interest in next-generation quantum cryptography, a communications method immune to eavesdropping, which enables unbreakable secure data sharing. Quantum cryptography is based on the concept of entangled photons, which are uniquely-coupled particles of light. The important property about entangled photons is the ability to gain knowledge about one photon when measuring the properties of the other photon. This uncommon behaviour is unique to quantum particles such as photons, and is at the core of secure quantum information technologies. To date, however, sources that efficiently produce entangled photons have not been fully developed due to lack of appropriate material systems, precision fabrication, or optical characterization approaches. This project overcomes these challenges through advanced photonic materials design and precise nanoscale synthesis of quantum dots in which entangled photons are created. The project activity also embraces the pedagogical efforts for outreach into the undergraduate, underrepresented, high-school and general community, with emphasis on underrepresented students in science and technology. Consistent cross-training of undergraduate and graduate students and new cross-disciplinary curricula development impact the scientific advances at the interface of mesoscopic materials and quantum sciences.Technical description: The generation of entangled photons is the cornerstone towards quantum communications, where the collapse of the photon wavefunction upon measurement or detection can be detected through channel monitoring. Much of the entangled photon sources, however, are based on spontaneous parametric downconversion. The spontaneous emission process is not deterministic and some degree of photon statistics - whether in Bell inequality measurements or tomography - is still needed, resulting in long-time counting and slow secure key rates. This project aims to tackle the challenge by demonstrating a deterministic entangled photon source based on a hybrid quantum dot-nanowire heterostructure. The first part of this project aims to demonstrate a hybrid quantum dot-nanowire heterostructure by selective area epitaxy for deterministic entangled photon generation. To achieve near-zero fine-structure splitting, the heterointerfaces and the geometry of quantum dots need to be carefully controlled by appropriate growth techniques. The second part of the research seeks to examine the photon correlation and measure the indistinguishability of the entangled photons generated in the mesoscopic solid-state implementation. The project also integrates the research with a pedagogical educational and outreach plan, including innovative outreach, training and mentoring of undergraduates and graduates, and a new graduate course on physics of quantum communication devices. Some examples of activities include hosting summer high school students to experience laboratory work, employing undergraduate students to fully participate in academic research, and developing a new graduate course: Mesoscopic Materials for Quantum Communications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.