757 research outputs found
Single-photon-level optical storage in a solid-state spin-wave memory
A long-lived quantum memory is a firm requirement for implementing a quantum
repeater scheme. Recent progress in solid-state rare-earth-ion-doped systems
justifies their status as very strong candidates for such systems. Nonetheless
an optical memory based on spin-wave storage at the single-photon-level has not
been shown in such a system to date, which is crucial for achieving the long
storage times required for quantum repeaters. In this letter we show that it is
possible to execute a complete atomic frequency comb (AFC) scheme, including
spin-wave storage, with weak coherent pulses of photons
per pulse. We discuss in detail the experimental steps required to obtain this
result and demonstrate the coherence of a stored time-bin pulse. We show a
noise level of photons per mode during storage, this
relatively low-noise level paves the way for future quantum optics experiments
using spin-waves in rare-earth-doped crystals
Atomic frequency comb memory with spin wave storage in 153Eu3+:Y2SiO5
153Eu3+:Y2SiO5 is a very attractive candidate for a long lived, multimode
quantum memory due to the long spin coherence time (~15 ms), the relatively
large hyperfine splitting (100 MHz) and the narrow optical homogeneous
linewidth (~100 Hz). Here we show an atomic frequency comb memory with spin
wave storage in a promising material 153Eu3+:Y2SiO5, reaching storage times
slightly beyond 10 {\mu}s. We analyze the efficiency of the storage process and
discuss ways of improving it. We also measure the inhomogeneous spin linewidth
of 153Eu3+:Y2SiO5, which we find to be 69 \pm 3 kHz. These results represent a
further step towards realising a long lived multi mode solid state quantum
memory.Comment: 7 pages and 7 figure
Phenomenological Lambda-Nuclear Interactions
Variational Monte Carlo calculations for (ground and
excited states) and are performed to decipher information on
-nuclear interactions. Appropriate operatorial nuclear and
-nuclear correlations have been incorporated to minimize the
expectation values of the energies. We use the Argonne two-body
NN along with the Urbana IX three-body NNN interactions. The study demonstrates
that a large part of the splitting energy in () is
due to the three-body NN forces. hypernucleus is
analyzed using the {\it s}-shell results. binding to nuclear matter
is calculated within the variational framework using the
Fermi-Hypernetted-Chain technique. There is a need to correctly incorporate the
three-body NN correlations for binding to nuclear matter.Comment: 18 pages (TeX), 2 figure
CHARACTERISTICS OF RURAL SUBSISTENCE SMALL HOLDER LIVESTOCK PRODUCTION SYSTEM IN MOUNTAINOUS AREAS OF NWFP, PAKISTAN
A study was conducted in the rural mountainous areas of North West Frontier Province of Pakistan to characterize small holder’s subsistence livestock production system. Livestock farmers (n=82) were interviewed in 16 villages of Batagram and Mansehra districts. The farmers were keeping on an average 4 buffalos, 1 cattle, 12 sheep or 13 goats per household. More than 94% farmers were keeping 4 buffaloes per household as compared to only 40% keeping 1 or 2 cattle. Buffaloes were main dairy animals producing 7.9 liters of milk/day or 2370 liters per lactation of 300 days. Local non-descript cows were producing only 2.5 liters of milk per day. Animals of all species were found to be underfed, as they depended mostly on self growing local grasses for grazing. Only milking animals were offered some concentrates in the form of cottonseed cake and wheat bran. Milk was mostly consumed at the household level or converted into butter oil. Age at first calving and calving interval of buffaloes were longer than those of cows. Incidence of livestock diseases was high in the area. Major diseases in cattle and buffaloes were haemorrhagic septicaemia and internal parasites. Pleuropneumonia and parasitism were major disease problems in small ruminants. It was estimated that gross profit averaged Rs. 32475 per buffalo, Rs. 3320 per sheep and Rs. 5314 per goat per year. Gross margin for cattle was negative and the farmers were sustaining a loss of Rs. 1960 per cow per year. Keeping in view the poor production environments, the overall performance of animals was encouraging and offered considerable scope for improvement
Microscopic calculations of Λ single-particle energies
A binding energy data for total baryon number A ≤ 208 and for Λ angular momenta ℓΛ ≤ 3 are analyzed in terms of phenomenological (but generally consistent with meson-exchange) ΛN and ΛNN potentials. The Fermi hypernetted chain technique is used to calculate the expectation values for the Λ binding to nuclear matter. Accurate effective ΛN and ΛNN potentials are obtained which are folded with the core-nucleus nucleon densities to calculate the Λ single-particle potential UΛ (r). We use a dispersive ANN potential but also include an explicit ρ dependence to allow for reduced repulsion in the surface, and the best fits have a large ρ dependence giving consistency with the variational Monte Carlo calculations for 5ΛHe. The exchange fraction of the ΛN space-exchange potential is found to be 0.2-0.3 corresponding to m*Λ ≃ (0.74 - 0.82)mΛ. Charge-symmetry breaking is found to be significant for heavy hypernuclei with a large neutron excess, with a strength consistent with that obtained from the A = 4 hypernuclei
Variational calculations of the -seperation energy of the O hypernucleus
Variational Monte Carlo calculations have been made for the O hypernucleus using realistic two- and three-baryon
interactions. A two pion exchange potential with spin- and space-exchange
components is used for the N potential. Three-body two-pion exchange
and strongly repulsive dispersive NN interactions are also included.
The trial wave function is constructed from pair- and triplet-correlation
operators acting on a single particle determinant. These operators consist of
central, spin, isospin, tensor and three- baryon potential components. A
cluster Monte Carlo method is developed for noncentral correlations and is used
with up to four-baryon clusters in our calculations. The three-baryon
NN force is discussed.Comment: 24 pages, 2 figs available by fax., for publication in Phys. Rev.
Magnetic damping of a carbon nanotube NEMS resonator
A suspended, doubly clamped single wall carbon nanotube is characterized at
cryogenic temperatures. We observe specific switching effects in dc-current
spectroscopy of the embedded quantum dot. These have been identified previously
as nano-electromechanical self-excitation of the system, where positive
feedback from single electron tunneling drives mechanical motion. A magnetic
field suppresses this effect, by providing an additional damping mechanism.
This is modeled by eddy current damping, and confirmed by measuring the
resonance quality factor of the rf-driven nano-electromechanical resonator in
an increasing magnetic field.Comment: 8 pages, 3 figure
Semi-Automated Needle Steering in Biological Tissue Using an Ultrasound-Based Deflection Predictor
The performance of needle-based interventions depends on the accuracy of needle tip positioning. Here, a novel needle steering strategy is proposed that enhances accuracy of needle steering. In our approach the surgeon is in charge of needle insertion to ensure the safety of operation, while the needle tip bevel location is robotically controlled to minimize the targeting error. The system has two main components: (1) a real-time predictor for estimating future needle deflection as it is steered inside soft tissue, and (2) an online motion planner that calculates control decisions and steers the needle toward the target by iterative optimization of the needle deflection predictions. The predictor uses the ultrasound-based curvature information to estimate the needle deflection. Given the specification of anatomical obstacles and a target from preoperative images, the motion planner uses the deflection predictions to estimate control actions, i.e., the depth(s) at which the needle should be rotated to reach the target. Ex-vivo needle insertions are performed with and without obstacle to validate our approach. The results demonstrate the needle steering strategy guides the needle to the targets with a maximum error of 1.22 mm
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