Methods and Applications of Multi-Photon Quantum State Synthesis

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We are developing a source for efficient creation of various single- and multi-photon states. This project is a culmination of the PI's past research on optimally engineered spontaneous parametric downconversion sources, high-efficiency photon detectors, and low-loss high-speed optical circuits. Specifically, the project implements a switched, temporally-multiplexed scheme that allows near-deterministic preparation of single-photon states. Combining four such states realizes the first efficient generation of heralded entangled photon pairs, a critical resource for many protocols in quantum information processing. Moreover, generalizations of the scheme enable preparation of a variety of other multi-photon states of interest. For instance, we can prepare exact energy eigenstates of the electromagnetic field, "Fock states," exponentially more efficiently than with present schemes relying on the simultaneous occurrence of improbable events; in fact, in the limit of lossless optics and perfect detectors, the method is 100% efficient. The central concept -- the ability to add (or subtract) photons one at a time -- can potentially be further extended to enable production of other multi-photon states of interest as well, as we are investigating. Single and entangled photons have become a central resource for experiments ranging from fundamental tests of quantum mechanics to optical quantum computing, from quantum cryptography to entanglement-enhanced quantum metrology. Despite recent advances, reliably and deterministically creating even simple optical states, e.g., single photons on demand, remains challenging. And while schemes to realize more complicated multi-photon states have been proposed, these typically scale exponentially poorly with the number of photons in this state. As a result, observed rates in experiments of this sort drop very quickly as the number of required photons increases, requiring minutes or hours to observe a single instance of the desired state. We are pursuing the efficient creation of various single- and multi-photon states, pushing the frontiers of quantum information processing in several different areas, including quantum communication, quantum metrology, and quantum computing. In addition to exploring a potentially transformative method for realizing true single- and multi-photon states, this project has the potential for broader impact beyond the "traditional" areas of quantum information processing, e.g., for human vision studies at the single-photon level. Bringing the realities of basic quantum information phenomena to students at an earlier age and in broader venues stimulates their interest in pursuing further knowledge in STEM areas.