Coherent manipulation of spin wave vector for polarization of photons in an atomic ensemble

We experimentally demonstrate the manipulation of two-orthogonal components of a spin wave in an atomic ensemble. Based on Raman two-photon transition and Larmor spin precession induced by magnetic field pulses, the coherent rotations between the two components of the spin wave is controllably achieved. Successively, the two manipulated spin-wave components are mapped into two orthogonal polarized optical emissions, respectively. By measuring Ramsey fringes of the retrieved optical signals, the \pi/2-pulse fidelity of ~96% is obtained. The presented manipulation scheme can be used to build an arbitrary rotation for qubit operations in quantum information processing based on atomic ensembles

Quantum Interference of Stored Coherent Spin-wave Excitations in a Two-channel Memory

Quantum memories are essential elements in long-distance quantum networks and quantum computation. Significant advances have been achieved in demonstrating relative long-lived single-channel memory at single-photon level in cold atomic media. However, the qubit memory corresponding to store two-channel spin-wave excitations (SWEs) still faces challenges, including the limitations resulting from Larmor procession, fluctuating ambient magnetic field, and manipulation/measurement of the relative phase between the two channels. Here, we demonstrate a two-channel memory scheme in an ideal tripod atomic system, in which the total readout signal exhibits either constructive or destructive interference when the two-channel SWEs are retrieved by two reading beams with a controllable relative phase. Experimental result indicates quantum coherence between the stored SWEs. Based on such phase-sensitive storage/retrieval scheme, measurements of the relative phase between the two SWEs and Rabi oscillation, as well as elimination of the collapse and revival of the readout signal, are experimentally demonstrated

Microstructural and Electron-Emission Characteristics of Nb-Si-N Films in Surface-Conduction Electron-Emitter Display

AbstractWe proposed ternary nitride Nb-Si-N film as a promising surface-conduction electron emitter (SCE) in surface-conduction electron-emitter display (SED). Nb-Si-N films consisted of continuous NbN polycrystalline phase with (Si3-xNb4x)N4 amorphous phase in NbN grain boundaries. After electroforming, serrated nanogaps were observed in Nb-Si-N SCE strips. The emission current of Nb-Si-N SCE array of 1×18 cells was 6.50μA with anode voltage of 1.5kV and device voltage of 22V, indicating satisfying potential for display applications comparing with NbN SCEs. © 2009 Published by Elsevier B.V