14,664 research outputs found
Semiempirical Modeling of Reset Transitions in Unipolar Resistive-Switching based Memristors
We have measured the transition process from the high to low resistivity states, i.e., the reset process of resistive switching based memristors based on Ni/HfO2/Si-n+ structures, and have also developed an analytical model for their electrical characteristics. When the characteristic curves are plotted in the current-voltage (I-V) domain a high variability is observed. In spite of that, when the same curves are plotted in the charge-flux domain (Q-phi), they can be described by a simple model containing only three parameters: the charge (Qrst) and the flux (rst) at the reset point, and an exponent, n, relating the charge and the flux before the reset transition. The three parameters can be easily extracted from the Q-phi plots. There is a strong correlation between these three parameters, the origin of which is still under study
Living up to their name: Profamilia takes on gender-based violence
This issue of Quality/Calidad/QualitĂ© describes the evolution of Profamilia through its work on gender-based violence in the Domincan Republic.Their project was conceived along two simultaneous paths: providing support services directly to women and girls who had experienced violence and initiating advocacy in the wider policy arena. Profamilia joined the commission that ultimately designed and promoted a law to increase protection against violence, especially domestic violence against women and children. Although the clinics now run a dynamic service program, the agency has also sustained its advocacy activities. Most of Profamiliaâs advocacy work is undertaken in partnership with other NGOs or with government agencies and has converted the organization from a family planning organization to a sexual and reproductive health organization that truly serves women
Exponential improvement in photon storage fidelities using subradiance and "selective radiance" in atomic arrays
A central goal within quantum optics is to realize efficient interactions
between photons and atoms. A fundamental limit in nearly all applications based
on such systems arises from spontaneous emission, in which photons are absorbed
by atoms and then re-scattered into undesired channels. In typical treatments
of atomic ensembles, it is assumed that this re-scattering occurs
independently, and at a rate given by a single isolated atom, which in turn
gives rise to standard limits of fidelity in applications such as quantum
memories or quantum gates. However, this assumption can be violated. In
particular, spontaneous emission of a collective atomic excitation can be
significantly suppressed through strong interference in emission. Thus far the
physics underlying the phenomenon of subradiance and techniques to exploit it
have not been well-understood. In this work, we provide a comprehensive
treatment of this problem. First, we show that in ordered atomic arrays in free
space, subradiant states acquire an interpretation in terms of optical modes
that are guided by the array, which only emit due to scattering from the ends
of the finite chain. We also elucidate the properties of subradiant states in
the many-excitation limit. Finally, we introduce the new concept of selective
radiance. Whereas subradiant states experience a reduced coupling to all
optical modes, selectively radiant states are tailored to simultaneously
radiate efficiently into a desired channel while scattering into undesired
channels is suppressed, thus enabling an enhanced atom-light interface. We show
that these states naturally appear in chains of atoms coupled to nanophotonic
structures, and we analyze the performance of photon storage exploiting such
states. We find that selectively radiant states allow for a photon storage
error that scales exponentially better with number of atoms than previously
known bounds.Comment: Fixed minor typos, is now analogous to published versio
Entanglement of two qubits mediated by one-dimensional plasmonic waveguides
We investigate qubit-qubit entanglement mediated by plasmons supported by
one-dimensional waveguides. We explore both the situation of spontaneous
formation of entanglement from an unentangled state and the emergence of driven
steady-state entanglement under continuous pumping. In both cases, we show that
large values for the concurrence are attainable for qubit-qubit distances
larger than the operating wavelength by using plasmonic waveguides that are
currently available.Comment: 4 pages, 4 figures. Minor Changes. Journal Reference added.
Highlighted in Physic
Faddeev eigenfunctions for point potentials in two dimensions
We present explicit formulas for the Faddeev eigenfunctions and related
generalized scattering data for point (delta-type) potentials in two
dimensions. In particular, we obtain the first explicit examples of such
eigenfunctions with contour singularity in spectral parameter at a fixed real
energy
Geometrically induced modification of surface plasmons in the optical and telecom regimes
We demonstrate that the introduction of a subwavelength periodic modulation
into a metallic structure strongly modifies the guiding characteristics of the
surface plasmon modes supported by the system. Moreover, it is also shown how a
new type of a tightly confined surface plasmon polariton mode can be created by
just milling a periodic corrugation into a metallic ridge placed on top of a
metal surface
Optimization of photon storage fidelity in ordered atomic arrays
A major application for atomic ensembles consists of a quantum memory for
light, in which an optical state can be reversibly converted to a collective
atomic excitation on demand. There exists a well-known fundamental bound on the
storage error, when the ensemble is describable by a continuous medium governed
by the Maxwell-Bloch equations. The validity of this model can break down,
however, in systems such as dense, ordered atomic arrays, where strong
interference in emission can give rise to phenomena such as subradiance and
"selective" radiance. Here, we develop a general formalism that finds the
maximum storage efficiency for a collection of atoms with discrete, known
positions, and a given spatial mode in which an optical field is sent. As an
example, we apply this technique to study a finite two-dimensional square array
of atoms. We show that such a system enables a storage error that scales with
atom number like ,
and that, remarkably, an array of just atoms in principle allows
for an efficiency comparable to a disordered ensemble with optical depth of
around 600.Comment: paper is now identical to published versio
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