4,196 research outputs found
Light-shift-induced photonic nonlinearities
We propose a new method to produce self- and cross-Kerr photonic
nonlinearities, using light-induced Stark shifts due to the interaction of a
cavity mode with atoms. The proposed experimental set-up is considerably
simpler than in previous approaches, while the strength of the nonlinearity
obtained with a single atom is the same as in the setting based on
electromagnetically induced transparency. Furthermore our scheme can be applied
to engineer effective photonic nonlinear interactions whose strength increases
with the number of atoms coupled to the cavity mode, leading to photon-photon
interactions several orders of magnitude larger than previously considered
possible.Comment: 4 pages, 4 figure
Quantum phase transitions with Photons and Polaritons
We show that a system of polaritons - combined atom and photon excitations -
in an array of coupled cavities, under an experimental set-up usually
considered in electromagnetically induced transparency, is described by the
Bose-Hubbard model. This opens up the possibility of using this system as a
quantum simulator, allowing for the observation of quantum phase transitions
and for the measurement of local properties, such as single site observables.
All the basic building blocks of the proposed setting have already been
achieved experimentally, showing the feasibility of its realization in the near
future.Comment: 7 pages, contribution for the proceedings of the QCMC0
Entanglement theory and the second law of thermodynamics
Entanglement is central both to the foundations of quantum theory and, as a novel resource, to quantum information science. The theory of entanglement establishes basic laws that govern its manipulation, in particular the non-increase of entanglement under local operations on the constituent particles. Such laws aim to draw from them formal analogies to the second law of thermodynamics; however, whereas in the second law the entropy uniquely determines whether a state is adiabatically accessible from another, the manipulation of entanglement under local operations exhibits a fundamental irreversibility, which prevents the existence of such an order. Here, we show that a reversible theory of entanglement and a rigorous relationship with thermodynamics may be established when considering all non-entangling transformations. The role of the entropy in the second law is taken by the asymptotic relative entropy of entanglement in the basic law of entanglement. We show the usefulness of this approach to general resource theories and to quantum information theory
Mutation of three amino acids in the disulfide-ring of a CNP based chimeric natriuretic peptide alters its vascular properties
Controlling the gap of fullerene microcrystals by applying pressure: the role of many-body effects
We studied theoretically the optical properties of C fullerene
microcrystals as a function of hydrostatic pressure with first-principles
many-body theories. Calculations of the electronic properties were done in the
GW approximation. We computed electronic excited states in the crystal by
diagonalizing the Bethe-Salpeter equation (BSE). Our results confirmed the
existence of bound excitons in the crystal. Both the electronic gap and optical
gap decrease continuously and non-linearly as pressure of up to 6 GPa is
applied. As a result, the absorption spectrum shows strong redshift. We also
obtained that "negative" pressure shows the opposite behavior: the gaps
increase and the optical spectrum shifts toward the blue end of the spectrum.
Negative pressure can be realized by adding cubane (CH) or other
molecules with similar size to the interstitials of the microcrystal. For the
moderate lattice distortions studied here, we found that the optical properties
of fullerene microcrystals with intercalated cubane are similar to the ones of
an expanded undoped microcrystal. Based on these findings, we propose doped C60
as active element in piezo-optical devices.Comment: Final version accepted by PRB. The review history is included in the
sourc
A Human Atrial Natriuretic Peptide Gene Mutation Reveals a Novel Peptide With Enhanced Blood Pressure-Lowering, Renal-Enhancing, and Aldosterone-Suppressing Actions
ObjectivesWe sought to determine the physiologic actions and potential therapeutic applications of mutant atrial natriuretic peptide (mANP).BackgroundThe cardiac hormone atrial natriuretic peptide (ANP) is a 28-amino acid (AA) peptide that consists of a 17-AA ring structure together with a 6-AA N-terminus and a 5-AA C-terminus. In a targeted scan for sequence variants within the human ANP gene, a mutation was identified that results in a 40-AA peptide consisting of native ANP(1-28)and a C-terminal extension of 12 AA. We have termed this peptide mutant ANP.MethodsIn vitro 3′,5′-cyclic guanosine monophosphate (cGMP) activation in response to mANP was studied in cultured human cardiac fibroblasts known to express natriuretic peptide receptor A. The cardiorenal and neurohumoral properties of mANP compared with ANP were assessed in vivo in normal dogs.ResultsWe observed an incremental in vitro cGMP dose response with increasing concentrations of mANP. In vivo with high-dose mANP (33 pmol/kg/min), we observed significantly greater plasma cGMP activation, diuretic, natriuretic, glomerular filtration rate enhancing, renin-angiotensin-aldosterone system inhibiting, cardiac unloading, and blood pressure lowering properties when compared with native ANP. Low-dose mANP (2 pmol/kg/min) has natriuretic and diuretic properties without altering systemic hemodynamics compared with no natriuretic or diuretic response with low-dose native ANP.ConclusionsThese studies establish that mANP activates cGMP in vitro and exerts greater and more sustained natriuretic, diuretic, glomerular filtration rate, and renal blood flow enhancing actions than native ANP in vivo
Entanglement theory and the second law of thermodynamics
Entanglement is central both to the foundations of quantum theory and, as a novel resource, to quantum information science. The theory of entanglement establishes basic laws that govern its manipulation, in particular the non-increase of entanglement under local operations on the constituent particles. Such laws aim to draw from them formal analogies to the second law of thermodynamics; however, whereas in the second law the entropy uniquely determines whether a state is adiabatically accessible from another, the manipulation of entanglement under local operations exhibits a fundamental irreversibility, which prevents the existence of such an order. Here, we show that a reversible theory of entanglement and a rigorous relationship with thermodynamics may be established when considering all non-entangling transformations. The role of the entropy in the second law is taken by the asymptotic relative entropy of entanglement in the basic law of entanglement. We show the usefulness of this approach to general resource theories and to quantum information theory
Consistency of the Regularization of Gauge Theories by High Covariant Derivatives
We show that regularization of gauge theories by higher covariant derivatives
and gauge invariant Pauli-Villars regulators is a consistent method if the
Pauli-Villars vector fields are considered in a covariant in the regulating
Pauli-Villars fields is pathological and the original Slavnov proposal in
covariant Landau gauge is not correct because of the appearance of massless
modes in the regulators which do not decouple when the ultraviolet regulator is
removed. In such a case the method does not correspond to the regularization of
a pure gauge theory but that of a gauge theory in interaction with massless
ghost fields. This explains the problems pointed out by Martin and Ruiz in
covariant Landau gauge. However, a minor modification of Slavnov method
provides a consistent regularization even for such a case. The regularization
that we introduce also solves the problem of overlapping divergences in a way
similar to geometric regularization and yields the standard values of the
and functions of the renormalization group equations.Comment: 20 pages, latex, 3 Postscript figures (expanded version
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