A closed-cycle, liquid helium cryocooler for next generation quantum light sources

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Technologies exploiting the exotic quantum mechanical properties of light and matter promise the revolutionize the way we process and share information. A quantum computers could exploit the Superposition Principle for massive parallelism and a corresponding quantum speed-up of problems that are intractable today; quantum communication can use Heisenberg's Uncertainty Relation to hide information for unbreakable cryptographic ciphers. Optical systems are central to quantum technologies, particularly those related to long-distance communication and interferometric metrology. Developing optimize quantum light sources, particularly single-photon sources, is crucial to their widespread application and success. Parametric down-conversion, a nonlinear optical process in which a high energy photon is split into a pair of lower energy photons, is the most common source of single and entangled photons today. It has some undesirable characteristics negatively impacting the performance of many quantum technologies: for example, it is inherently probabilistic and contains multiple photon emission. The next generation of quantum light sources needs to overcome these limitations. Promising systems to supersede downconversion can be broadly characterized as 'single emitters' or artificial atoms. These are quantum systems that, once excited, can emit one and only one photon to return to their ground state. We aim to exploit Indium Arsenide Phosphide quantum dots embedded in nanowires and defects in Boron Nitride sheets as single emitter single photon sources, to develop the next generation of single and entangled photon sources. Both of these systems must be cooled to cryogenic temperatures to suppress thermal noise and narrow spectral features. We will employ nonlinear optics techniques to shift and shape the spectral properties of the photons from these sources for quantum applications. This proposal requests funding for a closed-cycle liquid helium cryocooler capable of cooling these samples to 4K. The closed cycle system enables recycling of helium, reducing liquid helium expenses, and very long running times, essential for the expected long integration times of multiphoton experiments The proposed research would involve the full-time efforts of 3 PhD students and include at least one undergraduate or co-op work term each year. They will gain extensive experience and safety training with state-of-the-art cryogenics as well as lasers, optics, and single photon detection. It is anticipated that their work would be published in top-tier scientific journals.