Gaussian tripartite entanglement in the simultaneous measurement of position and momentum

In this work, we prove the generation of genuine tripartite continuous-variable entanglement in the unitary dynamics of the simultaneous measurement process of position and momentum observables raised by Arthurs and Kelly, considering a measurement configuration where the system under examination is a rotated, displaced, and squeezed vacuum state. Under these assumptions, the measurement configuration is entirely described by a Gaussian state. Then, through the positive partial transpose criterion (PPT), we certify genuine tripartite entanglement by testing the non-separability of the three $\left(1~ \text{vs}~2\right)$-mode bipartitions of the system. This process allows us to classify the qualitative properties of the entanglement in the category of fully inseparable Gaussian states according to the classification exposed in [Giedke et al., \href{https://link.aps.org/doi/10.1103/PhysRevA.64.052303}{Phys. Rev. A \textbf{64}, 052303 (2001)}]. Besides, we determine the quantitative entanglement properties of the system using the residual tripartite R{\'e}nyi-2 entanglement as a quantifier measure.Comment: 15 pages, 8 figure

Factorizing the time evolution operator

There is a widespread belief in the quantum physical community, and in textbooks used to teach Quantum Mechanics, that it is a difficult task to apply the time evolution operator Exp{-itH/h} on an initial wave function. That is to say, because the hamiltonian operator generally is the sum of two operators, then it is a difficult task to apply the time evolution operator on an initial wave function f(x,0), for it implies to apply terms operators like (a+b)^n. A possible solution of this problem is to factorize the time evolution operator and then apply successively the individual exponential operator on the initial wave function. However, the exponential operator does not directly factorize, i. e. Exp{a+b} is not equal to Exp{a}Exp{b}. In this work we present a useful procedure for factorizing the time evolution operator when the argument of the exponential is a sum of two operators, which obey specific commutation relations. Then, we apply the exponential operator as an evolution operator for the case of elementary unidimensional potentials, like the particle subject to a constant force and the harmonic oscillator. Also, we argue about an apparent paradox concerning the time evolution operator and non-spreading wave packets addressed previously in the literature.Comment: 24 pages; added references; one figure change

SU(2) coherent state path integrals labeled by a full set of Euler angles: basic formulation

We develop a basic formulation of the spin (SU(2)) coherent state path integrals based not on the conventional highest or lowest weight vectors but on arbitrary fiducial vectors. The coherent states, being defined on a 3-sphere, are specified by a full set of Euler angles. They are generally considered as states without classical analogues. The overcompleteness relation holds for the states, by which we obtain the time evolution of general systems in terms of the path integral representation; the resultant Lagrangian in the action has a monopole-type term a la Balachandran etal. as well as some additional terms, both of which depend on fiuducial vectors in a simple way. The process of the discrete path integrals to the continuous ones is clarified. Complex variable forms of the states and path integrals are also obtained. During the course of all steps, we emphasize the analogies and correspondences to the general canonical coherent states and path integrals that we proposed some time ago. In this paper we concentrate on the basic formulation. The physical applications as well as criteria in choosing fiducial vectors for real Lagrangians, in relation to fictitious monopoles and geometric phases, will be treated in subsequent papers separately.Comment: LaTex 2e; 28 pages. We rearrange the contents in such a way that one can grasp the whole results clearer than before by three theorems; All the appendices except one are incorporated into the body of the text. The contraction of the general SU(2) coherent state path integrals to those for the generic canonical coherent states is added. arXiv admin note: substantial text overlap with arXiv:quant-ph/990610

State transfer in dissipative and dephasing environments

By diagonalization of a generalized superoperator for solving the master equation, we investigated effects of dissipative and dephasing environments on quantum state transfer, as well as entanglement distribution and creation in spin networks. Our results revealed that under the condition of the same decoherence rate $\gamma$, the detrimental effects of the dissipative environment are more severe than that of the dephasing environment. Beside this, the critical time $t_c$ at which the transfer fidelity and the concurrence attain their maxima arrives at the asymptotic value $t_0=\pi/2\lambda$ quickly as the spin chain length $N$ increases. The transfer fidelity of an excitation at time $t_0$ is independent of $N$ when the system subjects to dissipative environment, while it decreases as $N$ increases when the system subjects to dephasing environment. The average fidelity displays three different patterns corresponding to $N=4r+1$, $N=4r-1$ and $N=2r$. For each pattern, the average fidelity at time $t_0$ is independent of $r$ when the system subjects to dissipative environment, and decreases as $r$ increases when the system subjects to dephasing environment. The maximum concurrence also decreases as $N$ increases, and when $N\rightarrow\infty$, it arrives at an asymptotic value determined by the decoherence rate $\gamma$ and the structure of the spin network.Comment: 12 pages, 6 figure

Interrelación de laboratorios de control y laboratorios de investigación en España para la armonización de metodologías de determinación de toxinas paralizantes

XII Congreso Nacional de Agricultura, Madrid 24-26 de noviembre de 2009Marketing of cultured and harvested shellfish is linked to monitoring programs for granting food safety. Its complexity requires constant cooperation between research and monitoring laboratories in order to improve sampling and analysing performances, achieve legal requirements, etc. for increasing consumer’s health protection but not reducing producer’s benefits. The JACUMAR project «Comparison of methodologies for the evaluation of Paralytic Shellfish Poisoning (PSP) toxins in bivalves. Application for aquaculture in Spain» groups research and monitoring laboratories from Galicia, Andalucía and Cataluña. Efforts are focused on detection and quantification of PSP toxins, searching an analytical method able to fulfil technical and management requirementsEste proyecto está financiado por la Junta Asesora de Cultivos Marinos (JACUMAR), y los programas de control por los gobiernos autónomos de Galicia, Andalucía y CataluñaN

Outcomes from elective colorectal cancer surgery during the SARS-CoV-2 pandemic

This study aimed to describe the change in surgical practice and the impact of SARS-CoV-2 on mortality after surgical resection of colorectal cancer during the initial phases of the SARS-CoV-2 pandemic