Grant: Discovery Grants Program - Individual

Quantum Information (QI) is a radically new way to communicate and process information. It is based on the laws of quantum mechanics which apply to atoms and light pulses that carry a minimal amount of energy and are called photons. Ordinary information technology processes bits that take either the value zero or one, but QI allows parallel processing of "qubits" that take all logical values simultaneously. This can be exploited for provably secure communication and a dramatic reduction in complexity of, e.g., search algorithms. Optical QI faces two major challenges. First, all-optical QI needs a device in which one photon can influence another photon. Because these light pulses are so faint this is difficult to achieve, but recent progress on gene- rating "giant optical nonlinearities" has brought us closer to its realization. Another challenge is the construc- tion of a "quantum repeater" which may enable quantum communication through optical fibers beyond the current limit of about 70 km distance. An essential part of a repeater is a "quantum memory" to store qubits. In our research project we will address both challenges. First, we will investigate two new ways to increase the influence of one photon on another. (i) Light near a thin metal layer can induce waves of charges which can increase the light's intensity and thus make it easier for photons to interact. We will study if this method is suitable despite the losses induced by the metal. (ii) Using a clever sequence of laser pulses it is possible to blow up atoms to a much larger size. Such "Rydberg atoms" can interact strongly even if they are relatively far apart from each other, and we will try to find a way to convert this interaction into an interaction between photons. Furthermore, we will extend our research program on building a quantum memory by searching for new ways to store photons in a gas of atoms or an ion-doped optical fiber by slowly changing control parameters such as an applied voltage or an additional laser beam.