Quantum Coherence and Entanglement with Atomic, Molecular and Optical Systems

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

This research program aims to understand and control quantum coherence and entangled states in atomic, molecular, and optical (AMO) systems. An entangled state of a compound subsystem is one that cannot be described in terms of separate realistic descriptions of its subsystems. Entangled states are central in studies of quantum information processing, which in addition to showing the way towards new technologies, such as quantum computers or quantum cryptography, may lead to deeper understanding of quantum mechanics. An important development in AMO Physics is the study of collective atomic-ensemble variables, which provide an interface between microscopic degrees of freedom, such as single-photon wave packets, and macroscopic degrees of freedom, such as electronic, vibrational or rotational, in a gas or vapor. Two themes are being pursued: (1) Mesoscopic-level entanglement of collective electronic excitation in the ground states of rubidium vapor, and (2) Exploration of a new platform--hollow core photonic crystal fibers--for use in quantum optics. Theme (1) seeks to extend recent experiments on number-state entanglement of atomic ensembles and optical fields at the one- and two-photon level to the 5-to-20 photon level. This requires state-of-the-art advances in both photon-number-resolving detection and in the measurement of higher-order field statistical moments. This tests the hypothesis that entanglement is a robust feature of nature even in the macroscopic world, but that detecting it becomes progressively more difficult technically as the excitation number becomes large. At some high excitation number, the quantum theory could either become irrelevant or break down. The experiment has several unique aspects: i) A new type of photon-number-resolving detector--a back-illuminated drift silicon photomultiplier--is being used to measure Stokes light pulses, thereby creating non-Gaussian atomic-ensemble entanglement in the 5-20 excitation-number regime. ii) To verify entanglement the researchers are developing balanced homodyne correlation, using a more practical scheme based on a CCD camera rather than multiple beam splitters as originally conceived. Theme (2) extends the research into a new promising area: hollow-core photonic crystal fibers (HC-PCF). In collaboration with a group at Bath University, the research team will undertake exploratory studies of rubidium-filled, hydrogen-filled, and xenon-filled HC-PCF. The long path lengths and tight, controlled optical confinement make these systems promising for ultralow-intensity nonlinear quantum optics, including creation of ultrawide-band comb-spectrum fields, photon pair generation, four-mode optical entanglement, atom-field entanglement, and others. The research will contribute broadly to the understanding of quantum entanglement and its measurement. This may impact studies of the foundations of quantum physics as well as quantum information science. Education of graduate students and undergraduate students is foremost in the planning of the project. Undergraduate students will be involved through REU programs. Important collaborative aspects of the project include close interaction with the theory group of Prof. Steven van Enk at the University of Oregon, experimental collaboration with Prof. F. Benabid at Bath University in England on HC-PCF, and technical collaboration with H.-G. Moser at Max Planck Institute in Garching, Germany on photon-number-resolving detectors. The PI is involved in various outreach efforts, including public lectures, new course development and textbook authoring, in an effort to bring physics to a wider audience. He is involved in international outreach through summer schools and research collaborations. And, the PI was founding Director of the Oregon Center for Optics at the UO, a synergistic center involving faculty and students from physics and chemistry.