All-Fiber Quantum Optics with Colloidal Nanosemiconductors

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Optical fibers are now commonly known as the Internet backbone transmitting light, whereas nanomaterials are a tool for customizing matter properties to generate innovative applications; this proposal is a meeting of both technologies towards the long term objective of generating photons on demand for information encoding, directly within optical fibers. A network of such fibers emitting and guiding light quanta, i.e. the photons, would be a step towards a quantum internet progressing from unbreakable cryptography to protect confidential information online. In this context, economists forecast an $8.2 billion quantum technology industry, employing 16 000 Canadians, by 2030. Current sources of single photons are all outside optical fibers, facing light coupling and portability challenges. Moreover, their architecture and most fabrication approaches are not so simple and scalable. These issues will be resolved with luminescent nanocrystal sources in optical fiber that can be easily spliced together. However, colloidal synthesis of semiconductor nanocrystals, namely quantum dots, has yet to deliver reliable quantum technological systems. Therefore, we will kill two birds with one stone by embedding the quantum dots in protective transparent plastic to be heated and drawn into an optical fiber. Indeed, the light emission rate will also accelerate and compete with the quenching of other mechanisms introducing unreliable fluctuations. Firstly, we will demonstrate control of this spontaneous emission rate with different optical fiber designs thanks to the Purcell effect. To verify the effect, photoluminescence decay traces of embedded quantum dot ensembles will be recorded at the fiber output. The concentration of quantum dots will be a key parameter to isolate them apart when drawing the optical fiber, then cutting them out into single photon sources as will be confirmed by their antibunching statistics. Secondly, mirror-like interfaces will be added at the ends of these sources to increase the light-matter coupling and accelerate the light emission even further. Different strategies to fabricate these resonating optical cavities, as found in lasers, will be compared in terms of generating individual and indistinguishable photons. Then, either the cavity modes or the quantum dot energy levels will be tuned into resonance with one another. A spectral anticrossing of levels and modes during tuning would then confirm a strong coupling. Thirdly, looking ahead towards encoding more information on a single photon or achieving more robust encoding on spin states, we will explore new methods to incorporate circular quantum rings and nanodiamonds, comprising nitrogen vacancy centers, in the polymer optical fibers. Finally in the shorter term, the cost-effective nanocrystal synthesis and fiber fabrication motivate the development of innovative sensing applications: an auspicious environment for local technology transfer and student-led entrepreneurship.