The deep space quantum link: prospective fundamental physics experiments using long-baseline quantum optics.

The National Aeronautics and Space Administration's Deep Space Quantum Link mission concept enables a unique set of science experiments by establishing robust quantum optical links across extremely long baselines. Potential mission configurations include establishing a quantum link between the Lunar Gateway moon-orbiting space station and nodes on or near the Earth. This publication summarizes the principal experimental goals of the Deep Space Quantum Link. These goals, identified through a multi-year design study conducted by the authors, include long-range teleportation, tests of gravitational coupling to quantum states, and advanced tests of quantum nonlocality.

Quantum probe of space-time curvature.

An atom interferometer measures the quantum phase due to gravitational time dilation.

Interference of clocks: A quantum twin paradox.

The phase of matter waves depends on proper time and is therefore susceptible to special-relativistic (kinematic) and gravitational (redshift) time dilation. Hence, it is conceivable that atom interferometers measure general-relativistic time-dilation effects. In contrast to this intuition, we show that (i) closed light-pulse interferometers without clock transitions during the pulse sequence are not sensitive to gravitational time dilation in a linear potential. (ii) They can constitute a quantum version of the special-relativistic twin paradox. (iii) Our proposed experimental geometry for a quantum-clock interferometer isolates this effect.

Circumventing Heisenberg's Uncertainty Principle in Atom Interferometry Tests of the Equivalence Principle.

Atom interferometry tests of universality of free fall based on the differential measurement of two different atomic species provide a useful complement to those based on macroscopic masses. However, when striving for the highest possible sensitivities, gravity gradients pose a serious challenge. Indeed, the relative initial position and velocity for the two species need to be controlled with extremely high accuracy, which can be rather demanding in practice and whose verification may require rather long integration times. Furthermore, in highly sensitive configurations gravity gradients lead to a drastic loss of contrast. These difficulties can be mitigated by employing wave packets with narrower position and momentum widths, but this is ultimately limited by Heisenberg's uncertainty principle. We present a promising scheme that overcomes these problems by compensating the effects of the gravity gradients and circumvents the fundamental limitations due to Heisenberg's uncertainty principle. Furthermore, it relaxes the experimental requirements on initial colocation by several orders of magnitude.

Nonequilibrium fluctuation-dissipation inequality and nonequilibrium uncertainty principle.

The fluctuation-dissipation relation is usually formulated for a system interacting with a heat bath at finite temperature, and often in the context of linear response theory, where only small deviations from the mean are considered. We show that for an open quantum system interacting with a nonequilibrium environment, where temperature is no longer a valid notion, a fluctuation-dissipation inequality exists. Instead of being proportional, quantum fluctuations are bounded below by quantum dissipation, whereas classically the fluctuations vanish at zero temperature. The lower bound of this inequality is exactly satisfied by (zero-temperature) quantum noise and is in accord with the Heisenberg uncertainty principle, in both its microscopic origins and its influence upon systems. Moreover, it is shown that there is a coupling-dependent nonequilibrium fluctuation-dissipation relation that determines the nonequilibrium uncertainty relation of linear systems in the weak-damping limit.

Initial-state preparation with dynamically generated system-environment correlations.

The dependence of the dynamics of open quantum systems upon initial correlations between the system and environment is an utterly important yet poorly understood subject. For technical convenience most prior studies assume factorizable initial states where the system and its environments are uncorrelated, but these conditions are not very realistic and give rise to peculiar behaviors. One distinct feature is the rapid buildup or a sudden jolt of physical quantities immediately after the system is brought in contact with its environments. The ultimate cause of this is an initial imbalance between system-environment correlations and coupling. In this paper we demonstrate explicitly how to avoid these unphysical behaviors by proper adjustments of correlations and/or the coupling, for setups of both theoretical and experimental interest. We provide simple analytical results in terms of quantities that appear in linear (as opposed to affine) master equations derived for factorized initial states.

2-aminohydroxamic acid derivatives as inhibitors of Bacillus cereus phosphatidylcholine preferred phospholipase C PC-PLC(Bc).

Phosphatidylcholine preferring phospholipase C (PC-PLC) is an important enzyme that plays a key role in a variety of cellular events and lipid homoeostases. Bacillus cereus phospholipase C (PC-PLC(Bc)) has antigenic similarity with the elusive mammalian PC-PLC, which has not thus far been isolated and purified. Therefore the discovery of inhibitors of PC-PLC(Bc) is of current interest. Here, we describe the synthesis and biological evaluation of a new type of compounds inhibiting PC-PLC(Bc). These compounds have been designed by evolution of previously described 2-aminohydroxamic acid PC-PLC(Bc) inhibitors that block the enzyme by coordination of the zinc active site atoms present in PC-PLC(Bc) [Gonzalez-Roura, A.; Navarro, I.; Delgado, A.; Llebaria, A.; Casas, J. Angew. Chem. Int. Ed.2004, 43, 862]. The new compounds maintain the zinc coordinating groups and possess an extra trimethylammonium function, linked to the hydroxyamide nitrogen by an alkyl chain, which is expected to mimic the trimethylammonium group of the phosphatidylcholine PC-PLC(Bc) substrates. Some of the compounds described inhibit the enzyme with IC(50)'s in the low micromolar range. Unexpectedly, the most potent inhibitors found are those that possess a trimethylammonium group but have chemically blocked the zinc coordinating functionalities. The results obtained suggest that PC-PLC(Bc) inhibition is not due to the interaction of compounds with the phospholipase catalytic zinc atoms, but rather results from the inhibitor cationic group recognition by the PC-PLC(Bc) amino acids involved in choline lipid binding.

Synthesis and phospholipase C inhibitory activity of D609 diastereomers.

The potassium xanthate D609 is widely accepted as a selective inhibitor of PC-specific phospholipase C (PC-PLC). The tricyclo[5.2.1.(02,6)]decane skeleton present in D609 can lead to four diastereomeric pairs, but the diastereoselectivity of PC-PLC inhibition has never been reported. In this article, the synthesis of racemic D609 diastereomers and that of other xanthates, as well as their inhibitory effect on PC-PLC is reported. All xanthates obtained were competitive inhibitors of PC-PLC from Bacillus cereus (PLCBc). No significant differences were found in the activity of D609 diastereomers (Ki 13-17 microM), suggesting the absence of a diastereochemical control of the enzyme by xanthate inhibitors. This result was confirmed after obtaining other potassium xanthates differing from D609 in the aliphatic chain. Among them, the potassium O-n-decenylxanthate was the most active inhibitor of PLCBc (Ki 10 microM). These data indicate that the essential structural requirements for PLCBc in vitro inhibition by xanthates are the presence of a Zn-chelating dithiocarbonate head and a sufficiently hydrophobic aliphatic moiety.

Dissipation, noise, and vacuum decay in quantum field theory.

We study the process of vacuum decay in quantum field theory focusing on the stochastic aspects of the interaction between long- and short-wavelength modes. This interaction results in a diffusive behavior of the reduced Wigner function describing the state of long-wavelength modes, and thereby to a finite activation rate even at zero temperature. This effect can make a substantial contribution to the total decay rate.

Tratamiento hormonal sustitutivo en la prevención de la cardiopatía isquémica en la mujer. Argumentos a favor / Hormone Replacement Therapy in Ischemic Heart Disease Prevention in Women: Arguments in Favour

Numerosas evidencias han constatado las acciones fisiológicas de los esteroides sexuales sobre el sistema cardiovascular. Por otro lado, la coherencia de los resultados de muchos estudios epidemiológicos objetivan una acción positiva de estradiol sobre la aparición de la enfermedad cardiovascular, específicamente sobre la inhibición de la aterosclerosis y el control del funcionamiento de la pared vascular. Desde un punto de vista experimental, algunos ensayos clínicos han demostrado una acción positiva del estradiol sobre variables intermedias de riesgo cardiovascular, como la hipercolesterolemia o la hipertensión. Sin embargo, las conclusiones del ensayo HERS, primer estudio sobre prevención secundaria de estradiol sobre la enfermedad cardiovascular, no han demostrado una acción positiva eficaz y han puesto en entredicho las pretendidas acciones favorables del tratamiento hormonas sustitutivo en pacientes cardiópatas posmenopáusicas. A pesar de todo, este ensayo adolece de puntos débiles importantes que lo han convertido, para algunos autores, en un estudio no conclusivo. Por tanto, en el momento actual no es posible tomar una decisión basada en la evidencia sobre la pregunta clave de la acción preventiva de los esteroides sexuales sobre la enfermedad cardiovascular en la posmenopausia (AU)