ITR - Integrated Source of High-fidelity Entangled States for Quantum Information Processing

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0312556SergienkoEntanglement studies in quantum physics have benefited greatly from the use of photon pairs generated via the nonlinear optical process of spontaneous parametric down-conversion (SPDC). Applications include distributed imaging, metrology, cryptography, and computing. The integration of quantum cryptography into real-world telecommunications networks, and making quantum-optical computing processors scalable, can be fostered by reducing their size and developing an integrated source of high-quality entangled photon states. A few initial implementations of SPDC in periodically-poled nonlinear waveguides in the collinear copropagating configuration have demonstrated several advantages. Both the rate of photon-pair production and the single-mode fiber coupling efficiency are increased substantially. However, the generated photons are usually correlated in time but not entangled. Moreover, the spectral bandwidth is also rather large. This precludes their use in a telecommunication environment where such states are highly susceptible to chromatic and polarization-mode dispersion.This research aims at overcoming these problems by developing a novel integrated source of high-fidelity entangled photons. The new approach makes use of counterpropagating quasi-phase matching in periodically poled nonlinear waveguides. The use of transverse pumping, and of a type-II nonlinear interaction, allows the production of polarization-entangled photon pairs that exit symmetrically from opposite sides of a nonlinear waveguide, ready for coupling into single-mode optical fiber. The spectral bandwidth of the photons generated in this configuration is reduced by more than an order of magnitude, thereby allowing dispersion-insensitive quantum communications.Intellectual merit. The use of an integrated source of high-fidelity entangled photons will enhance real-world scalable network performance by incorporating quantum technology into the existing fabric of telecommunication systems. The development of such a device will open a path toward the creation of a dense population of entangled sources and elementary quantum-optical computing gates on a chip. This, in turn, will hasten the appearance of the first compact quantum-optical computers.Broader Impact. This program will provide students with unique multidisciplinary experiences in the application of cutting-edge quantum-optical techniques to a broad range of problems in modern optics and telecommunications.Research milestones. i) investigation of physical effects and design specific geometries leading to generation of quantum states entangled both in frequency and in polarization; ii) production of miniature sources of high-intensity narrow bandwidth polarization-entangled states using a counterpropagating interaction inside the periodically poled nonlinear waveguide; iii) demonstration of enhanced performance of quantum cryptography and entanglement swapping at telecommunication wavelengths using new source.