Ultrashort Single Photon Generation via Conditional Excitation of an Atomic Barium Ensemble

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This project explores the use of an atomic barium ensemble as a scalable source of pure ultrashort single photons and the creation, preservation and detection of various types of entanglement between distant photons, atomic ensembles and combinations of both. By applying an off-resonant ultrashort laser pulse to warm atomic barium vapor, we generate a collective excitation in the atomic ensemble, called a spin wave, together with a quantum of electromagnetic excitation, i.e. a photon. The detection of the photon signals a successful event and the presence of the spin wave in the matter. This long-lived collective excitation can be converted into an ultrashort single photon in a pure wave-packet at a later desired time by applying another ultrashort pulse. By combining numerous atomic ensembles, we are able to create multiple pure ultrashort and identical photons synchronously, an essential requirement for high bit-rate quantum computation and communication applications. The broad bandwidth of the involved fields permits us to study the spectral properties of nonclassical correlations between the created photon and the atomic excitation, adding to our understanding and ability to control the properties of light-matter interaction at the quantum level.The work of this project provides and demonstrates a method to generate photons suitable for high-speed quantum communication and computation operations, such as entanglement swapping and Bell state measurements. These applications are essential components of protocols such as quantum teleportation, quantum cryptography and Bell inequality detection. Through this project graduate and undergraduate students are trained in experimental and theoretical ultrafast quantum optics and atomic physics. The project serves as the basis for an undergraduate tutorial at the University of Delaware to motivate and improve student understanding of quantum mechanics.