157 research outputs found
Efficient quantum memory using a weakly absorbing sample
A light-storage experiment with a total (storage and retrieval) efficiency
is carried out by enclosing a sample, with a single pass
absorption of 10%, in an impedance-matched cavity. The experiment is carried
out using the Atomic Frequency Comb (AFC) technique in a praseodymium-doped
crystal () and the cavity is created by reflection
coating the crystal surfaces. The AFC technique has previously by far
demonstrated the highest multi-mode capacity of all quantum memory concepts
tested experimentally. We claim that the present work shows that it is
realistic to create efficient, on-demand, long storage time AFC memories
Statistical modeling and theoretical analysis of the influence of laser phase fluctuations on photon echo data erasure and stimulated photon echoes
The effect of random laser phase fluctuations on stimulated photon echoes (SPEs) and on coherently added SPEs was studied and evaluated both experimentally and analytically with statistical methods. The general concept of describing laser frequency fluctuations as a stationary stochastic process is presented and applied to three specific SPE configurations. The effect of phase fluctuations on erasing an SPE by coherently adding another SPE, phase-shifted by 180 degrees relative to the first, is presented
Using electric fields for pulse compression and group velocity control
In this article, we experimentally demonstrate a new way of controlling the
group velocity of an optical pulse by using a combination of spectral hole
burning, slow light effect and linear Stark effect in a rare-earth-ion-doped
crystal. The group velocity can be changed continuously by a factor of 20
without significant pulse distortion or absorption of the pulse energy. With a
similar technique, an optical pulse can also be compressed in time. Theoretical
simulations were developed to simulate the group velocity control and the pulse
compression processes. The group velocity as well as the pulse reshaping are
solely controlled by external voltages which makes it promising in quantum
information and quantum communication processes. It is also proposed that the
group velocity can be changed even more in an Er doped crystal while at the
same time having a transmission band matching the telecommunication wavelength.Comment: 8 pages, 7 figure
Observation of a magnetic-field-induced resonance in the homogeneous dephasing time for the D-1(2)-H-3(4) transition in Pr3+:YAlO3
Using two-pulse photon echo excitation a strong resonance in the measured homogeneous dephasing time as a function of magnetic field is observed in the H-3(4)-D-1(2) transition of Pr3+:YAlO3. The resonance could only be observed at low excitation energies since it otherwise was masked by excitation intensity dependent extra dephasing processes in the crystal. Thus intensity dependent dephasing processes may not only affect the apparent dephasing time of a system but may also mask other more subtle interactions in the materials studied. It is reasonable to assume that the type of resonance observed could be caused by Zeeman induced level crossings in the active ion or in the host crystal ions or, possibly, that it could be due to coincidences between Zeeman level transition frequencies. However, based on current data of the Pr:YAlO3 system the observed resonance could not be unambiguously tied to such effects
Fast all-optical nuclear spin echo technique based on EIT
We demonstrate an all-optical Raman spin echo technique, using
Electromagnetically Induced Transparency (EIT) to create the different pulses
of the spin echo sequence: initialization, pi-rotation, and readout. The first
pulse of the sequence induces coherence directly from a mixed state, and the
technique is used to measure the nuclear spin coherence of an inhomogeneously
broadened ensemble of rare-earth ions (Pr). In contrast to previous
experiments it does not require any preparatory hole burning pulse sequences,
which greatly shortens the total duration of the sequence. The effect of the
different pulses is characterized by quantum state tomography and is compared
with simulations. We demonstrate two applications of the technique by using the
spin echo sequence to accurately compensate a magnetic field across our sample,
and to measure the coherence time at high temperatures up to 11 K, where
standard preparation techniques are difficult to implement. We explore the
potential of the technique and possible applications.Comment: 8 pages, 6 figure
Cavity enhanced storage - preparing for high efficiency quantum memories
Cavity assisted quantum memory storage has been proposed [PRA 82, 022310
(2010), PRA 82, 022311 (2010)] for creating efficient (close to unity) quantum
memories using weakly absorbing materials. Using this approach we
experimentally demonstrate a significant (about 20-fold) enhancement in quantum
memory efficiency compared to the no cavity case. A strong dispersion
originating from absorption engineering inside the cavity was observed, which
directly affect the cavity line-width. A more than 3 orders of magnitude
reduction of cavity mode spacing and cavity line-width from GHz to MHz was
observed. We are not aware of any previous observation of several orders of
magnitudes cavity mode spacing and cavity line-width reduction due to slow
light effects.Comment: 13 pages, 5 figure
Spectroscopic measurements of streamer filaments in electric breakdown in a dielectric liquid
Emission spectroscopy has been utilized to provide information about the electron density and temperature in streamers and breakdown arcs in transformer oil. Recorded spectra include strongly broadened hydrogen Balmer-alpha lines and vibration/rotation band profiles of the C-2 molecule. The origin of the observed broadening of hydrogen lines is discussed and it is concluded that it arises mainly from collisions with charged particles, so-called dynamic Stark broadening. By assuming that the broadening is due solely to dynamic Stark broadening, electron densities between 1 x 10(18) and 1 x 10(19) cm(-3) were obtained for the rear of positive streamer filaments during the later stages of propagation. For negative streamers we obtained an upper limit of 3 x 10(16) cm(-3) and for breakdown arcs electron densities up to 4 x 10(18) cm(-3). The temperature information in the C-2 emission profiles and the intensity ratio of the hydrogen Balmer lines are discussed. Rough estimations of the temperature are presented both for positive and for negative streamers
Deep tissue imaging with acousto-optical tomography and spectral hole burning with slow light effect: a theoretical study
Biological tissue is a highly scattering medium that prevents deep imaging of light. For medical applications, optical imaging offers a molecular sensitivity that would be beneficial for diagnosing and monitoring of diseases. Acousto-optical tomography has the molecular sensitivity of optical imaging with the resolution of ultrasound and has the potential for deep tissue imaging. Here, we present a theoretical study of a system that combines acousto-optical tomography and slow light spectral filters created using spectral hole burning methods. Using Monte Carlo simulations, a model to obtain the contrast-to-noise ratio (CNR) deep in biological tissue was developed. The simulations show a CNR  >  1 for imaging depths of ∼5  cm in a reflection mode setup, as well as, imaging through ∼12 cm in transmission mode setups. These results are promising and form the basis for future experimental studies
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