Waveguides in periodically poled lithium niobate can be used for frequency up- and downconversion of quantum states of light.We discuss applications for single-photon detection, quantum communications, and limitations due to parasitic noise processes.
Global quantum communication can provide information theoretical security worldwide and thus is one ultimate goal for the field of quantum information. One of the main challenge toward this goal is the frequency mismatch. In this talk, I shall briefly introduce Periodically Poled Lithium Niobate (PPLN) waveguide based frequency conversion and its applications, including up-conversion single photon detector, measurement device independent quantum key distribution (QKD), long distance free space QKD and telecomband interface for cold atom quantum memory.
The quantum nature of light at the single photon level allows for unique applications that classical physics neither predicts nor describes. Most notably, appropriate conditions may cause the states of photons with indistinguishable properties to become entangled, enabling novel approaches to quantum computation, secure communications, and metrology. \n \nAny operational quantum information network transporting entangled-photon states must establish a high-fidelity link between its distant nodes despite the inherent fragility of entangled states. However, the lack of a universal operating wavelength for all optical devices makes this a substantial challenge. Telecommunication fibers, entangled photon pair sources, quantum optical memories, and quantum repeaters all function in disparate spectral windows dictated by the properties of the materials used to fabricate them. Quantum frequency conversion (QFC), the single-photon limit of nonlinear parametric sum and difference frequency generation in optics, offers a bridge between spectral regions with full preservation of quantum state character, including entanglement. \n \nPeriodically poled optical waveguides in ferroelectric crystals are versatile tools in nonlinear optics. Confining the nonlinear interaction to a waveguide greatly enhances its efficiency compared to bulk optics. Periodic poling, the process of periodically inverting the domains of a ferroelectric medium using a strong electric field, enables a variety of quasi-phase matching configurations to engineer a desired nonlinear interaction. \n \nThis work concentrates on the design, development, fabrication, and characterization of a titanium-diffused periodically poled lithium niobate (Ti:PPLN) waveguide device. This device is designed to execute single-step quantum frequency conversion from 369.5nm to 1550nm in order to facilitate a quantum state transfer between standard fiber telecommunication wavelengths and an atomic quantum memory system employing trapped ytterbium ions. \n \nThe creation of phase matching conditions for such an extreme distance in frequency demands precise control of high magnitude electric fields on the single-micron scale. As the first demonstration of its kind in Ti:PPLN, the development of these devices included novel improvements to existing fabrication methods, improving the state-of-the-art of precision, quality, and yield for poling of ferroelectric crystals.
We demonstrate 1500 nm band single-photon detection with low dark-count noise and a potentially high efficiency, which may allow long distance and high-bit-rate quantum key distribution. By developing frequency upconversion devices based on periodically poled lithium niobate waveguides, which are specifically designed to use a pump wavelength longer than that of communication-band photons, we completely eliminate the dark-count noise caused by parasitic nonlinear processes in the waveguide. We observed an internal conversion efficiency as high as 40% and demonstrated scaling down to the single photon level while maintaining a background dark-count rate of 10(2)s(-1).