Dual-Species Matter Qubit Entangled with Light

School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA.
Physical Review Letters (Impact Factor: 7.51). 04/2007; 98(12):123602. DOI: 10.1103/PhysRevLett.98.123602
Source: PubMed


We propose and demonstrate an atomic qubit based on a cold
$^{85}$Rb-$^{87}$Rb isotopic mixture, entangled with a frequency-encoded
optical qubit. The interface of an atomic qubit with a single spatial light
mode, and the ability to independently address the two atomic qubit states,
should provide the basic element of an interferometrically robust quantum

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    ABSTRACT: Quantum communication between two remote locations often involves remote parties sharing an entangled quantum state. At present, entanglement distribution is usually performed using photons transmitted through optical fibers. However, the absorption of light in the fiber limits the communication distances to less than 200 km, even for optimal photon telecom wavelengths. To increase this distance, the quantum repeater idea was proposed. In the quantum repeater architecture, one divides communication distance into segments of the order of the attenuation length of the photons and places quantum memory nodes at the intermediate locations. Since the photon loss between intermediate locations is low, it is possible then to establish entanglement between intermediate quantum memory nodes. Once entanglement between adjacent nodes is established, one can extend it over larger distances using entanglement swapping. The long coherence time of a quantum memory is a crucial requirement for the quantum repeater protocol. It is obvious that the coherence time of a quantum memory should be much longer that the time it takes for light to travel between remote locations. For a communication distance l = 1000 km, the corresponding time is t = l/c = 3.3 ms. One can show that for a simple repeater protocol and realistic success probabilities of entanglement generation, the required coherence time should be on the order of many seconds, while for the more complicated protocols that involve multiplexing and several quantum memory cells per intermediate node, the required coherence time is on the order of milliseconds. In this thesis, I describe a quantum memory based on an ensemble of rubidium atoms confined in a one-dimensional optical lattice. The use of the magnetically- insensitive clock transition and suppression of atomic motion allows us to increase coherence time of the quantum memory by two-orders of magnitude compared to previous work. I also propose a method for determining the Zeeman content of atomic samples. In addition, I demonstrate the observation of quantum evolution under continuous measurement. The long quantum memory lifetime demonstrated in this work opens the way for scalable processing of quantum information and long distance quantum communication.
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    ABSTRACT: Since the development of quantum mechanics almost a century ago, there has been considerable controversy over the interpretations and predictions of quantum theory. Owing to the counterintuitive predictions of quantum mechanics, Einstein himself even wondered if this theory should be considered complete. While these questions have troubled many physicists over the past century, the development of the new field of quantum information science and the applications that may result from large scale quantum systems have brought many of these fundamental questions of quantum mechanics to the mainstream of not only theoretical but also experimental physics. This thesis deals with a system at the heart of these questions - the first demonstration of quantum entanglement of two individual massive particles at a distance. I describe a theoretical and experimental framework for entanglement of two particles using trapped atomic ions. Trapped ions are among the most attractive systems for scalable quantum information protocols because they can be well isolated from the environment and manipulated easily with lasers. Using our trapped ion system, I show the first explicit demonstration of quantum entanglement between matter and light using a single ion and its single emitted photon. Further, by combining two such ion-photon entangled systems, I demonstrate the entanglement of two remotely located ions. These entanglement protocols, together with the recent developments of trapped ion quantum computing, can be used to create a platform for a scalable quantum information network, and perhaps confront some of the strangest features of quantum mechanics. Ph.D. Physics University of Michigan, Horace H. Rackham School of Graduate Studies
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    ABSTRACT: We demonstrate a novel way to efficiently create a robust entanglement between an atomic and a photonic qubit. A single laser beam is used to excite one atomic ensemble and two different modes of Raman fields are collected to generate the atom-photon entanglement. With the help of built-in quantum memory, the entanglement still exists after 20.5 micros storage time which is further proved by the violation of Clauser-Horne-Shimony-Holt type Bell's inequality. The entanglement procedure can serve as a building block for a novel robust quantum repeater architecture [Zhao, Phys. Rev. Lett. 98, 240502 (2007)10.1103/PhysRevLett.98.240502] and can be extended to generate high-dimensional atom-photon entanglements.
    Physical Review Letters 11/2007; 99(18):180505. DOI:10.1103/PHYSREVLETT.99.180505 · 7.51 Impact Factor
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