We describe the generation of entangled and hyperentangled photon pairs using a microstructure-fiber Sagnac
interferometer, which is formed by a polarizing beam splitter and a highly nonlinear microstructure fiber twisted
by 90° from end to end. This interferometer allows two identical four-wave mixing processes to occur on the same
fiber principal axis, ensuring perfect spatial and temporal mode matching of the two four-wave mixing outputs
on the polarizing beam splitter to create entanglement over the entire four-wave mixing phase-matching spectral
range. With an average pump power of 220 μW, we measure a two-photon coincidence rate of 1 kHz with ▵λ =
0.9 nm. Two-photon interference visibilities exceed 91% for polarization-entangled photon pairs generated from
this source, and are > 84% for both time-bin and polarization degrees of freedom for hyperentangled photons,
all without subtracting accidental coincidences.
We theoretically investigate the feasibility of using spectral hole burning in Pr3+:Y2SiO5 to prepare an ensemble
of Pr3+ ions with a spectral distribution optimized for use as a quantum memory for single-photon states. We
introduce figures of merit for the spectral distribution of the Pr3+ ions when used as a quantum-memory node
in a Duan-Lukin-Cirac-Zoller-type quantum-repeater scheme. Finally, we describe progress toward optimizing
the hole-burning sequence by using a computational model of the hole-burning process to calculate these figures
of merit over a wide range of parameters.
We describe the preparation of a high spectral brightness, broad wavelength coverage, single-spatial mode source of polarization-entangled photon pairs operated at room temperature. The source takes advantage of single-mode fiber optics, highly nonlinear microstructure fiber, judicious phase-matching, and the inherent stability provided by a Sagnac interferometer. With a modest average pump power (300 μW), we create all four Bell states with a detected two-photon coincidence rate of 7 kHz per bandwidth of 0.9 nm, in a spectral range of more than 20 nm.
In the emerging field of quantum information technology the two basic subfields are quantum communication
and quantum computation. Photonic qubits are considered as most promising information carriers for this
new technology due to the immense advantage of suffering negligible decoherence. Additionally, the very small
photon-photon interactions can be replaced by inducing effective nonlinearities via measurements which allow for
the implementation of crucial two-qubit gate operations. Although the spontaneous parametric down-conversion
gives access to the generation of highly entangled few-photon states, such as four-qubit cluster states which
allow to demonstrate the new concept of the one-way quantum computer, its applicability is highly limited
due to the poor scaling of the simultaneous emission of more than one-entangled photon pair. Therefore of
particular interest is the reversible mapping of qubits from photon states to atomic states. This might allow
the implementation of photonic quantum repeaters for long-distance quantum communication or the generation
of arbitrary multi-photon states as required for linear-optics quantum computing. Thus for the realization of
such a quantum network several approaches for achieving the required quantum control between matter and
photons have been studied during the past few years. Recent experiments demonstrating the generation of
narrow-bandwidth single photons using a room-temperature ensemble of 87Rb atoms and electromagnetically
induced transparency should emphasize the progress towards such a quantum network.
KEYWORDS: Chemical species, Single photon, Beam splitters, Raman scattering, Raman spectroscopy, Pulsed laser operation, Avalanche photodetectors, Photodetectors, Solids, Signal to noise ratio
We describe proof-of principle experiments demonstrating a novel approach for generating pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. The approach is based on preparation of an atomic ensemble in a state with a desired number of atomic spin excitations, which is later converted into a photon pulse by exploiting long-lived coherent memory for photon states and electromagnetically induced transparency (EIT). We discuss our progress toward applying these techniques to transmit quantum states between atomic memory nodes connected by a photonic channel.
KEYWORDS: Raman spectroscopy, Signal detection, Rubidium, Signal processing, Chemical species, Raman scattering, Signal attenuation, Quantum memory, Quantum communications
We present experimental work that investigates whether quantum
information carried by light can be stored via reversible mapping
of the quantum state of such light onto a collective atomic
coherence. Such a quantum memory could be utilized to allow quantum communication over long, lossy channels. Current efforts concentrate on writing a photon-number-squeezed state of light onto a collective coherence between the ground-state hyperfine levels of
87Rb atoms in a warm vapor cell, and subsequent on-demand retrieval of this light. In this approach, intensity squeezing between the written and retrieved photon fields provides evidence for storage of a photon-number-squeezed state of light. The scheme is based on spontaneous Raman transitions that create the atomic coherence, and at the same time convert control fields into signal fields that propagate under conditions of electromagnetically induced transparency. We present experimental results demonstrating the storage and retrieval of light using this method, and discuss techniques for measuring intensity squeezing between these photon fields.
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