QnTM: Entanglement in mesoscopic atomic clouds and quantum networking

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The scientific goal of this proposal is to demonstrate and study techniques that will be important for building networks that can reliably transmit quantum information over macroscopic distances. Neutral atoms that have been laser cooled and stored in optical traps have low decoherence rates and are well suited for storing quantum information in the form of qubits. In order to transfer information between macroscopically separated neutral atom qubits the information can be mapped onto photons that are emitted by one atom and detected by the receiving atom. As individual atoms have small cross sections for photon generation and detection we have proposed and will demonstrate coupling of single atoms to mesoscopic many atom qubits, followed by efficient generation of photonic qubits by the mesoscopic ensemble. The emitted photon is then detected by a receiving ensemble, which is in turn coupled to a single atom qubit. Combining these elements will enable a quantum channel that connects single atom qubits. The quantum channel can be used for transmitting quantum information and for creating distant bell states that can be used for teleportation of the atomic states. Our experimental approach is based on using single atoms as well as ensembles of atoms stored at high densities in optical traps. The atoms are laser cooled to kinetic energies of a few micro Kelvins. Coherent laser techniques are used for qubit manipulation as well as excitation of strongly interacting Rydberg states. The Rydberg states are used to couple information between single atoms and many atom ensembles. Coherent manipulation of the ensembles with several laser beams results in deterministic emission of photons in a desired direction. The intellectual merit of the proposed activity is in the study and demonstration of many particle entanglement. The presence of entanglement provides a sharp distinction between classical and quantum phenomena, and is fundamental to the computational power of quantum mechanical systems. This research will extend our ability to create and harness entanglement for controlling the flow of information and will demonstrate the possibility of entangling single atom qubits with mesocopic qubits.The broader impact of the proposed activity will include contributions to the development of quantum techniques for computing and communication. These quantum mechanical approaches have the potential for unprecedented computational power, as well as secure transmission of information. In addition the research to be performed at The University of Wisconsin - Madison will expose undergraduate students, graduate students, and postdoctoral researchers to state of the art techniques and tools, and train them to contribute to the technological and scientific development of society. We have consistently had strong involvement of undergraduate students in our research on this topic and will continue to do so in the proposed work.