Phase-dependent decoherence of optical transitions in Pr3+:LaF3 in the presence of a driving field

The decoherence times of orthogonally phased components of the optical transition dipole moment in a two-level system have been observed to differ by an order of magnitude. This phase anisotropy is observed in coherent transient experiments where an optical driving field is present during extended periods of decoherence. The decoherence time of the component of the dipole moment in phase with the driving field is extended compared to T_2, obtained from two-pulse photon echoes, in analogy with the spin locking technique of NMR.Comment: 5 pages, 2 figures; replaced with published versio

Demonstration of conditional quantum phase shift between ions in a solid

Due to their potential for long coherence times, dopant ions have long been considered promising candidates for scalable solid state quantum computing. However, the demonstration of two qubit operation has proven to be problematic, largely due to the difficulty of addressing closely spaced ions. Here we use optically active ions and optical frequency addressing to demonstrate a conditional phase shift between two qubits

Grid Cells Form a Global Representation of Connected Environments.

The firing patterns of grid cells in medial entorhinal cortex (mEC) and associated brain areas form triangular arrays that tessellate the environment [1, 2] and maintain constant spatial offsets to each other between environments [3, 4]. These cells are thought to provide an efficient metric for navigation in large-scale space [5-8]. However, an accurate and universal metric requires grid cell firing patterns to uniformly cover the space to be navigated, in contrast to recent demonstrations that environmental features such as boundaries can distort [9-11] and fragment [12] grid patterns. To establish whether grid firing is determined by local environmental cues, or provides a coherent global representation, we recorded mEC grid cells in rats foraging in an environment containing two perceptually identical compartments connected via a corridor. During initial exposures to the multicompartment environment, grid firing patterns were dominated by local environmental cues, replicating between the two compartments. However, with prolonged experience, grid cell firing patterns formed a single, continuous representation that spanned both compartments. Thus, we provide the first evidence that in a complex environment, grid cell firing can form the coherent global pattern necessary for them to act as a metric capable of supporting large-scale spatial navigation

The nitrogen-vacancy center in diamond re-visited

Symmetry considerations are used in presenting a model of the electronic structure and the associated dynamics of the nitrogen-vacancy center in diamond. The model accounts for the occurrence of optically induced spin polarization, for the change of emission level with spin polarization and for new measurements of transient emission. The rate constants given are in variance to those reported previously.Comment: 12 pages 10 figure

Photon Echoes Produced by Switching Electric Fields

We demonstrate photon echoes in Eu$^{3+}$:Y$_{2}$SiO$_{5}$ by controlling the inhomogeneous broadening of the Eu$^{3+}$ $^{7}$F$_{0}\leftrightarrow^{5}$D$_{0}$ optical transition. This transition has a linear Stark shift and we induce inhomogeneous broadening by applying an external electric field gradient. After optical excitation, reversing the polarity of the field rephases the ensemble, resulting in a photon echo. This is the first demonstration of such a photon echo and its application as a quantum memory is discussed.Comment: improved introduction, including theoretical outline of the relvant quantum memory proposa