ABSTRACT

Quantum information science (QIS) promises means for storing, transmitting, and processing information in ways not achievable using conventional (classical-physics-based) information technology. Success in QIS could revolutionize both technology and science through new computation and communication capabilities. Major breakthroughs are still needed before these can become reality. It is generally recognized that the most powerful quantum computation will take place using material systems (atoms or electrons). In contrast, quantum communication across a network (a "Quantum Internet") will take place using light (photons). In addition, specialized quantum-information processing will take place using light or a combination of light and interacting atoms, as needed, for example, to construct signal repeaters for extending the range of quantum communication over longer distances. This project will develop a radical, yet practical, new approach to using photons to encode quantum information.

Photons in a light beam have four distinct properties, any of which could be used to encode quantum-information: polarization (e.g., vertical or horizontal), two-dimensions of beam profile (spatial shape), and temporal shape (variation in time of brightness during a light pulse). In order to fully utilize light for transmitting information in a quantum network, it is necessary to be able to manipulate and sort a beam of light according to the states associated with each of these properties. While polarization and spatial beam profiles have been previously developed as means for encoding quantum information on photons, the temporal shape of photons has gone largely unrecognized as an important potential technique. The project endeavors to complete the "tool kit" for photon-based QIS by developing means to use photon temporal shape to encode information. This approach has predicted benefits in that 1) it allows more than one bit of information to be encoded on a single photon, 2) the encoding method is robust against the alterations of light that occur while traveling in a long optical fiber, and 3) the method nicely interfaces with atom-based quantum-light memories, which will be used in the future construction of a Quantum Internet.

Controlling quantum systems is of broad interest in science and information technology, metrology, quantum chemistry, and nano-mechanics. Optical technology and quantum-optics-based information science offer excellent opportunities to integrate research with science education. To improve the quality of general science education for non-science majors, the P.I. cofounded in 2010 the Science Literacy Program (SLP) at the University of Oregon, and serves as its Co-Director. The SLP has provided mentored instructional opportunities to many graduate students and undergraduate science majors serving as co-instructors in science literacy courses. He developed and taught an SLP course, Quantum Physics for Everyone, which presented quantum information science to non-science majors, using active learning techniques to engage the students. He will continue serving as SLP Co-Director.

From a more technical perspective, the project will develop the idea that in QIS, temporal modes (TMs) of photons, and more generally light fields, should be viewed on an equal footing with polarization and transverse modes. TMs are wave-packet modes that have the same carrier frequency, polarization, and transverse spatial mode, and occupy the same time bin, but yet are temporal orthogonal. To enable the development of TMs for use as qubits and qudits, the central needed technology is the quantum pulse gate (QPG), which will implement a near-100% efficient spatial sorting of field-orthogonal TMs. Based on their recently proposed method of temporal-mode interferometry (TMI), the researchers will demonstrate the elements of a complete quantum information framework that employs field orthogonality of single-photon temporal modes. The three requirements - generation of resource states, the targeted and efficient manipulation of TMs, and their detection and characterization - can be fulfilled with current technology. In particular, the researchers will study, experimentally and theoretically, means for implementing single-qubit quantum-logic operations (Pauli-X, -Y, and -Z gates; and phase-shift gate) using the quantum pulse gate device as the basic building block. They will also demonstrate that the QPG can act as a real-time controllable switch that is temporal-mode selective, by varying a phase shift internal to the device. In addition, they will demonstrate means for verifying the fidelity of such gate operations, using a new form of quantum-state tomography, which can determine the quantum state directly in a TM basis.

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