145 research outputs found
Cloning quantum entanglement in arbitrary dimensions
We have found a quantum cloning machine that optimally duplicates the
entanglement of a pair of -dimensional quantum systems. It maximizes the
entanglement of formation contained in the two copies of any
maximally-entangled input state, while preserving the separability of
unentangled input states. Moreover, it cannot increase the entanglement of
formation of all isotropic states. For large , the entanglement of formation
of each clone tends to one half the entanglement of the input state, which
corresponds to a classical behavior. Finally, we investigate a local
entanglement cloner, which yields entangled clones with one fourth the input
entanglement in the large- limit.Comment: 6 pages, 3 figure
Influence of the Precursor (Nature and Amount) on the Morphology of MoO<sub>3</sub> Crystallites Supported on Silica
Evolution of a spinor condensate: coherent dynamics, dephasing and revivals
We present measurements and a theoretical model for the interplay of spin
dependent interactions and external magnetic fields in atomic spinor
condensates. We highlight general features like quadratic Zeeman dephasing and
its influence on coherent spin mixing processes by focusing on a specific
coherent superposition state in a F=1 Rb Bose-Einstein condensate. In
particular, we observe the transition from coherent spinor oscillations to
thermal equilibration
Ghost imaging using homodyne detection
We present a theoretical study of ghost imaging based on correlated beams
arising from parametric down-conversion, and which uses balanced homodyne
detection to measure both the signal and idler fields. We analytically show
that the signal-idler correlations contain the full amplitude and phase
information about an object located in the signal path, both in the near-field
and the far-field case. To this end we discuss how to optimize the optical
setups in the two imaging paths, including the crucial point regarding how to
engineer the phase of the idler local oscillator as to observe the desired
orthogonal quadrature components of the image. We point out an inherent link
between the far-field bandwidth and the near-field resolution of the reproduced
image, determined by the bandwidth of the source of the correlated beams.
However, we show how to circumvent this limitation by using a spatial averaging
technique which dramatically improves the imaging bandwidth of the far-field
correlations as well as speeds up the convergence rate. The results are backed
up by numerical simulations taking into account the finite size and duration of
the pump pulse.Comment: 17 pages, 10 figures, submitted to Phys. Rev.
Cloning a real d-dimensional quantum state on the edge of the no-signaling condition
We investigate a new class of quantum cloning machines that equally duplicate
all real states in a Hilbert space of arbitrary dimension. By using the
no-signaling condition, namely that cloning cannot make superluminal
communication possible, we derive an upper bound on the fidelity of this class
of quantum cloning machines. Then, for each dimension d, we construct an
optimal symmetric cloner whose fidelity saturates this bound. Similar
calculations can also be performed in order to recover the fidelity of the
optimal universal cloner in d dimensions.Comment: 6 pages RevTex, 1 encapuslated Postscript figur
Kinetic theory and dynamic structure factor of a condensate in the random phase approximation
We present the microscopic kinetic theory of a homogeneous dilute Bose
condensed gas in the generalized random phase approximation (GRPA), which
satisfies the following requirements: 1) the mass, momentum and energy
conservation laws; 2) the H-theorem; 3) the superfluidity property and 4) the
recovery of the Bogoliubov theory at zero temperature \cite{condenson}. In this
approach, the condensate influences the binary collisional process between the
two normal atoms, in the sense that their interaction force results from the
mediation of a Bogoliubov collective excitation traveling throughout the
condensate. Furthermore, as long as the Bose gas is stable, no collision
happens between condensed and normal atoms. In this paper, we show how the
kinetic theory in the GRPA allows to calculate the dynamic structure factor at
finite temperature and when the normal and superfluid are in a relative motion.
The obtained spectrum for this factor provides a prediction which, compared to
the experimental results, allows to validate the GRPA.
PACS numbers:03.75.Hh, 03.75.Kk, 05.30.-dComment: 6 pages, 1 figures, QFS2004 conferenc
Thermodynamics of a Bose-Einstein Condensate with Weak Disorder
We consider the thermodynamics of a homogeneous superfluid dilute Bose gas in
the presence of weak quenched disorder. Following the zero-temperature approach
of Huang and Meng, we diagonalize the Hamiltonian of a dilute Bose gas in an
external random delta-correlated potential by means of a Bogoliubov
transformation. We extend this approach to finite temperature by combining the
Popov and the many-body T-matrix approximations. This approach permits us to
include the quasi-particle interactions within this temperature range. We
derive the disorder-induced shifts of the Bose-Einstein critical temperature
and of the temperature for the onset of superfluidity by approaching the
transition points from below, i.e., from the superfluid phase. Our results lead
to a phase diagram consistent with that of the finite-temperature theory of
Lopatin and Vinokur which was based on the replica method, and in which the
transition points were approached from above.Comment: 11 pages, 5 figure
Combination, Modulation and Interplay of Modern Radiotherapy with the Tumor Microenvironment and Targeted Therapies in Pancreatic Cancer: Which Candidates to Boost Radiotherapy?
Pancreatic ductal adenocarcinoma cancer (PDAC) is a highly diverse disease with low tumor immunogenicity. PDAC is also one of the deadliest solid tumor and will remain a common cause of cancer death in the future. Treatment options are limited, and tumors frequently develop resistance to current treatment modalities. Since PDAC patients do not respond well to immune checkpoint inhibitors (ICIs), novel methods for overcoming resistance are being explored. Compared to other solid tumors, the PDAC's tumor microenvironment (TME) is unique and complex and prevents systemic agents from effectively penetrating and killing tumor cells. Radiotherapy (RT) has the potential to modulate the TME (e.g., by exposing tumor-specific antigens, recruiting, and infiltrating immune cells) and, therefore, enhance the effectiveness of targeted systemic therapies. Interestingly, combining ICI with RT and/or chemotherapy has yielded promising preclinical results which were not successful when translated into clinical trials. In this context, current standards of care need to be challenged and transformed with modern treatment techniques and novel therapeutic combinations. One way to reconcile these findings is to abandon the concept that the TME is a well-compartmented population with spatial, temporal, physical, and chemical elements acting independently. This review will focus on the most interesting advancements of RT and describe the main components of the TME and their known modulation after RT in PDAC. Furthermore, we will provide a summary of current clinical data for combinations of RT/targeted therapy (tRT) and give an overview of the most promising future directions
Quantum spiral bandwidth of entangled two-photon states
We put forward the concept of quantum spiral bandwidth of the spatial mode
function of the two-photon entangled state in spontaneous parametric
downconversion. We obtain the bandwidth using the eigenstates of the orbital
angular momentum of the biphoton states, and reveal its dependence with the
length of the down converting crystal and waist of the pump beam. The
connection between the quantum spiral bandwidth and the entropy of entanglement
of the quantum state is discussed.Comment: 10 pages, 3 figure
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