1,790 research outputs found
NMR investigation of contextuality in a quantum harmonic oscillator via pseudospin mapping
Physical potentials are routinely approximated to harmonic potentials so as
to analytically solve the system dynamics. Often it is important to know when a
quantum harmonic oscillator (QHO) behaves quantum mechanically and when
classically. Recently Su et. al. [Phys. Rev. A {\bf 85}, 052126 (2012)] have
theoretically shown that QHO exhibits quantum contextuality (QC) for a certain
set of pseudospin observables. In this work, we encode the four eigenstates of
a QHO onto four Zeeman product states of a pair of spin-1/2 nuclei. Using the
techniques of NMR quantum information processing, we then demonstrate the
violation of a state-dependent inequality arising from the noncontextual hidden
variable model, under specific experimental arrangements. We also
experimentally demonstrate the violation of a state-independent inequality by
thermal equilibrium states of nuclear spins, thereby assessing their
quantumness.Comment: 5 Pages, 3 Figures, context dependency illustrated, error below eq. 5
correcte
Local tetragonal distortion in La_{0.7}Sr_{0.3}MnO_3 strained thin films probed by x-ray absorption spectroscopy
We report on an angular resolved X-ray Absorption Spectroscopy study of
thin films epitaxially grown by pulsed laser
deposition on slightly mismatched substrates which induce tensile or
compressive strains. XANES spectra give evidence of tetragonal distortion
within the octahedra, with opposite directions for tensile and
compressive strains. Quantitative analysis has been done and a model of
tetragonal distortion reflecting the strain has been established. EXAFS data
collected in plane for tensile substrate confirm the change in the
average bond distance and the increase of length matching with the
enlargement of the cell parameter. From these results we conclude that there is
no significant change in the angle. Our observations conflict with
the scenarios which this angle is the main driving parameter in the sensitivity
of manganite films properties to external strains and suggest that the
distortion within the octahedra plays a key role in the modification of the
transport and magnetic properties.Comment: 8 pages, 6 figure
Benchmarking quantum control methods on a 12-qubit system
In this letter, we present an experimental benchmark of operational control
methods in quantum information processors extended up to 12 qubits. We
implement universal control of this large Hilbert space using two complementary
approaches and discuss their accuracy and scalability. Despite decoherence, we
were able to reach a 12-coherence state (or 12-qubits pseudo-pure cat state),
and decode it into an 11 qubit plus one qutrit labeled observable pseudo-pure
state using liquid state nuclear magnetic resonance quantum information
processors.Comment: 11 pages, 4 figures, to be published in PR
Geometric quantum computation using fictitious spin- 1/2 subspaces of strongly dipolar coupled nuclear spins
Geometric phases have been used in NMR, to implement controlled phase shift
gates for quantum information processing, only in weakly coupled systems in
which the individual spins can be identified as qubits. In this work, we
implement controlled phase shift gates in strongly coupled systems, by using
non-adiabatic geometric phases, obtained by evolving the magnetization of
fictitious spin-1/2 subspaces, over a closed loop on the Bloch sphere. The
dynamical phase accumulated during the evolution of the subspaces, is refocused
by a spin echo pulse sequence and by setting the delay of transition selective
pulses such that the evolution under the homonuclear coupling makes a complete
rotation. A detailed theoretical explanation of non-adiabatic geometric
phases in NMR is given, by using single transition operators. Controlled phase
shift gates, two qubit Deutsch-Jozsa algorithm and parity algorithm in a
qubit-qutrit system have been implemented in various strongly dipolar coupled
systems obtained by orienting the molecules in liquid crystal media.Comment: 37 pages, 17 figure
Carrier relaxation dynamics in defect states of epitaxial GaN/AlN/Si using ultrafast transient absorption spectroscopy
The relaxation dynamics of the carriers through the defect levels in an epitaxial GaN film grown with an AlN buffer layer on Si has been performed on the femto-picosecond timescale, using ultrafast transient absorption spectroscopy (UFTS). The sample was pumped above and below the band gap and probed with a white light continuum (480-800 nm). A combination of bi and triple exponential decay functions at different probe wavelengths were used to fit the kinetic profile of the carriers in the defect continuum. Based on the UFTS measurements, a model is proposed which explains the dynamics in the shallow traps and deep level defects. Furthermore, to determine the role of the lattice in the relaxation dynamics, the experiment was conducted at a low lattice temperature of 4.2 K. The relaxation constants from the UFTS measurements confirm not only the presence of shallow and deep level defects but also the involvement of phonons in one of the relaxation processes
Low-density series expansions for directed percolation I: A new efficient algorithm with applications to the square lattice
A new algorithm for the derivation of low-density series for percolation on
directed lattices is introduced and applied to the square lattice bond and site
problems. Numerical evidence shows that the computational complexity grows
exponentially, but with a growth factor \lambda < \protect{\sqrt[8]{2}},
which is much smaller than the growth factor \lambda = \protect{\sqrt[4]{2}}
of the previous best algorithm. For bond (site) percolation on the directed
square lattice the series has been extended to order 171 (158). Analysis of the
series yields sharper estimates of the critical points and exponents.Comment: 20 pages, 8 figures (3 of them > 1Mb
Influence of sediment chemistry on mangrove-phosphobacterial relationship
The study reveals importance of sediment chemistry in mangrove-phosphobacterial relationship. The various physicochemical parameters of sediment, bacterial distribution, and acidic- alkaline phosphatase activity were studied in Avicennia marina mangrove sediments. The sampling sites were four mangrove forests along West India. Rhizospheric, pneumatophoric and bulk/non-rhizospheric sediment were collected. The rhizospheric sediment showed higher bacterial activity. The pH was observed low in the rhizospheric sediment and good abundance of phosphate-solubilizing bacteria (PSB). This was also supported by other physico-chemical parameters. Acid phosphatase activity was found to be higher in rhizospheric sediment indicating acid production at rhizosphere by microbial action and root exudation. It is the first study indicating that alkaline phosphatase activity was observed to be higher in pneumatophoric sediment. This coincides with higher number of phosphatase-producing bacteria (PPB) and high inorganic P in the pneumatophoric sediment, revealing that this region of A. marina harbours favourably more PPB with utilization of organic P by bacterial load and conversion to inorganic forms stressing that strong bonding exists between mangrove-sediment-phosphobacterial relationships
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