1,502 research outputs found
Fluorescence molecular tomography: Principles and potential for pharmaceutical research
Fluorescence microscopic imaging is widely used in biomedical research to study molecular and cellular processes in cell culture or tissue samples. This is motivated by the high inherent sensitivity of fluorescence techniques, the spatial resolution that compares favorably with cellular dimensions, the stability of the fluorescent labels used and the sophisticated labeling strategies that have been developed for selectively labeling target molecules. More recently, two and three-dimensional optical imaging methods have also been applied to monitor biological processes in intact biological organisms such as animals or even humans. These whole body optical imaging approaches have to cope with the fact that biological tissue is a highly scattering and absorbing medium. As a consequence, light propagation in tissue is well described by a diffusion approximation and accurate reconstruction of spatial information is demanding. While in vivo optical imaging is a highly sensitive method, the signal is strongly surface weighted, i.e., the signal detected from the same light source will become weaker the deeper it is embedded in tissue, and strongly depends on the optical properties of the surrounding tissue. Derivation of quantitative information, therefore, requires tomographic techniques such as fluorescence molecular tomography (FMT), which maps the three-dimensional distribution of a fluorescent probe or protein concentration. The combination of FMT with a structural imaging method such as X-ray computed tomography (CT) or Magnetic Resonance Imaging (MRI) will allow mapping molecular information on a high definition anatomical reference and enable the use of prior information on tissue’s optical properties to enhance both resolution and sensitivity. Today many of the fluorescent assays originally developed for studies in cellular systems have been successfully translated for experimental studies in animals. The opportunity of monitoring molecular processes non-invasively in the intact organism is highly attractive from a diagnostic point of view but even more so for the drug developer, who can use the techniques for proof-of-mechanism and proof-of-efficacy studies. This review shall elucidate the current status and potential of fluorescence tomography including recent advances in multimodality imaging approaches for preclinical and clinical drug development
Entanglement detection in coupled particle plasmons
When in close contact, plasmonic resonances interact and become strongly
correlated. In this work we develop a quantum mechanical model, using the
language of continuous variables and quantum information, for an array of
coupled particle plasmons. This model predicts that when the coupling strength
between plasmons approaches or surpasses the local dissipation, a sizable
amount of entanglement is stored in the collective modes of the array. We also
prove that entanglement manifests itself in far-field images of the plasmonic
modes, through the statistics of the quadratures of the field, in what
constitutes a novel family of entanglement witnesses. This protocol is so
robust that it is indeed independent of whether our own model is correct.
Finally, we estimate the amount of entanglement, the coupling strength and the
correlation properties for a system that consists of two or more coupled
nanospheres of silver, showing evidence that our predictions could be tested
using present-day state-of-the-art technology.Comment: 8 pages (6 main text + 2 supplemental), 3 figure
Klein tunneling and Dirac potentials in trapped ions
We propose the quantum simulation of the Dirac equation with potentials,
allowing the study of relativistic scaterring and the Klein tunneling. This
quantum relativistic effect permits a positive-energy Dirac particle to
propagate through a repulsive potential via the population transfer to
negative-energy components. We show how to engineer scalar, pseudoscalar, and
other potentials in the 1+1 Dirac equation by manipulating two trapped ions.
The Dirac spinor is represented by the internal states of one ion, while its
position and momentum are described by those of a collective motional mode. The
second ion is used to build the desired potentials with high spatial
resolution.Comment: 4 pages, 3 figures, minor change
Coupling single molecule magnets to quantum circuits
In this work we study theoretically the coupling of single molecule magnets
(SMMs) to a variety of quantum circuits, including microwave resonators with
and without constrictions and flux qubits. The main results of this study is
that it is possible to achieve strong and ultrastrong coupling regimes between
SMM crystals and the superconducting circuit, with strong hints that such a
coupling could also be reached for individual molecules close to constrictions.
Building on the resulting coupling strengths and the typical coherence times of
these molecules (of the order of microseconds), we conclude that SMMs can be
used for coherent storage and manipulation of quantum information, either in
the context of quantum computing or in quantum simulations. Throughout the work
we also discuss in detail the family of molecules that are most suitable for
such operations, based not only on the coupling strength, but also on the
typical energy gaps and the simplicity with which they can be tuned and
oriented. Finally, we also discuss practical advantages of SMMs, such as the
possibility to fabricate the SMMs ensembles on the chip through the deposition
of small droplets.Comment: 23 pages, 12 figure
Split vortices in optically coupled Bose-Einstein condensates
We study a rotating two-component Bose-Einstein condensate in which an
optically induced Josephson coupling allows for population transfer between the
two species. In a regime where separation of species is favored, the ground
state of the rotating system displays domain walls with velocity fields normal
to them. Such a configuration looks like a vortex split into two halves, with
atoms circulating around the vortex and changing their internal state in a
continuous way.Comment: 4 EPS pictures, 4 pages; Some errata have been corrected and thep
resentation has been slightly revise
Quantum simulation of the Klein paradox with trapped ions
We report on quantum simulations of relativistic scattering dynamics using
trapped ions. The simulated state of a scattering particle is encoded in both
the electronic and vibrational state of an ion, representing the discrete and
continuous components of relativistic wave functions. Multiple laser fields and
an auxiliary ion simulate the dynamics generated by the Dirac equation in the
presence of a scattering potential. Measurement and reconstruction of the
particle wave packet enables a frame-by-frame visualization of the scattering
processes. By precisely engineering a range of external potentials we are able
to simulate text book relativistic scattering experiments and study Klein
tunneling in an analogue quantum simulator. We describe extensions to solve
problems that are beyond current classical computing capabilities.Comment: 3 figures, accepted for publication in PR
Split Instability of a Vortex in an Attractive Bose-Einstein Condensate
An attractive Bose-Einstein condensate with a vortex splits into two pieces
via the quadrupole dynamical instability, which arises at a weaker strength of
interaction than the monopole and the dipole instabilities. The split pieces
subsequently unite to restore the original vortex or collapse.Comment: 4 pages, 4 figures, added figures and references, revised tex
Structural instability of vortices in Bose-Einstein condensates
In this paper we study a gaseous Bose-Einstein condensate (BEC) and show
that: (i) A minimum value of the interaction is needed for the existence of
stable persistent currents. (ii) Vorticity is not a fundamental invariant of
the system, as there exists a conservative mechanism which can destroy a vortex
and change its sign. (iii) This mechanism is suppressed by strong interactions.Comment: 4 pages with 3 figures. Submitted to Phys. Rev. Let
Quantum Simulation of Quantum Field Theories in Trapped Ions
We propose the quantum simulation of a fermion and an antifermion field modes
interacting via a bosonic field mode, and present a possible implementation
with two trapped ions. This quantum platform allows for the scalable add-up of
bosonic and fermionic modes, and represents an avenue towards quantum
simulations of quantum field theories in perturbative and nonperturbative
regimes.Comment: To be published in Physical Review Letter
Transport coefficients of multi-particle collision algorithms with velocity-dependent collision rules
Detailed calculations of the transport coefficients of a recently introduced
particle-based model for fluid dynamics with a non-ideal equation of state are
presented. Excluded volume interactions are modeled by means of biased
stochastic multiparticle collisions which depend on the local velocities and
densities. Momentum and energy are exactly conserved locally. A general scheme
to derive transport coefficients for such biased, velocity dependent collision
rules is developed. Analytic expressions for the self-diffusion coefficient and
the shear viscosity are obtained, and very good agreement is found with
numerical results at small and large mean free paths. The viscosity turns out
to be proportional to the square root of temperature, as in a real gas. In
addition, the theoretical framework is applied to a two-component version of
the model, and expressions for the viscosity and the difference in diffusion of
the two species are given.Comment: 31 pages, 8 figures, accepted by J. Phys. Cond. Matte
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