144,209 research outputs found
Spatial mode storage in a gradient echo memory
Three-level atomic gradient echo memory (lambda-GEM) is a proposed candidate
for efficient quantum storage and for linear optical quantum computation with
time-bin multiplexing. In this paper we investigate the spatial multimode
properties of a lambda-GEM system. Using a high-speed triggered CCD, we
demonstrate the storage of complex spatial modes and images. We also present an
in-principle demonstration of spatial multiplexing by showing selective recall
of spatial elements of a stored spin wave. Using our measurements, we consider
the effect of diffusion within the atomic vapour and investigate its role in
spatial decoherence. Our measurements allow us to quantify the spatial
distortion due to both diffusion and inhomogeneous control field scattering and
compare these to theoretical models.Comment: 11 pages, 9 figure
Information Storage and Retrieval for Probe Storage using Optical Diffraction Patterns
A novel method for fast information retrieval from a probe storage device is
considered. It is shown that information can be stored and retrieved using the
optical diffraction patterns obtained by the illumination of a large array of
cantilevers by a monochromatic light source. In thermo-mechanical probe
storage, the information is stored as a sequence of indentations on the polymer
medium. To retrieve the information, the array of probes is actuated by
applying a bending force to the cantilevers. Probes positioned over
indentations experience deflection by the depth of the indentation, probes over
the flat media remain un-deflected. Thus the array of actuated probes can be
viewed as an irregular optical grating, which creates a data-dependent
diffraction pattern when illuminated by laser light. We develop a low
complexity modulation scheme, which allows the extraction of information stored
in the pattern of indentations on the media from Fourier coefficients of the
intensity of the diffraction pattern. We then derive a low-complexity maximum
likelihood sequence detection algorithm for retrieving the user information
from the Fourier coefficients. The derivation of both the modulation and the
detection schemes is based on the Fraunhofer formula for data-dependent
diffraction patterns. We show that for as long as the Fresnel number F<0.1, the
optimal channel detector derived from Fraunhofer diffraction theory does not
suffer any significant performance degradation.Comment: 14 pages, 11 figures. Version 2: minor misprints corrected,
experimental section expande
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
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