Improving the precision of frequency estimation via long-time coherences

In the last years several estimation strategies have been formulated to determine the value of an unknown parameter in the most precise way, taking into account the presence of noise. These strategies typically rely on the use of quantum entanglement between the sensing probes and they have been shown to be optimal in the asymptotic limit in the number of probes, as long as one performs measurements on shorter and shorter time scales. Here, we present a different approach to frequency estimation, which exploits quantum coherence in the state of each sensing particle in the long time limit and is obtained by properly engineering the environment. By means of a commonly used master equation, we show that our strategy can overcome the precision achievable with entanglement-based strategies for a finite number of probes. We discuss a possible implementation of the scheme in a realistic setup that uses trapped ions as quantum sensors.Comment: 11+3 pages, 2 figure

Шляхи підвищення конкурентоспроможності підприємства

Objective: Elevated levels of the vascular cell adhesion molecule-1 (VCAM-1) in women with preeclampsia may reflect endothelial damage and leukocyte activation. Urinary VCAM-1 excretion in normal pregnancies and those complicated by hypertension has not been studied. We studied the circadian pattern of VCAM-1 levels in the serum and urinary excretion of VCAM-1 in normal pregnancies and those complicated by hypertension and analyzed their relation with maternal blood pressure. Methods: Serum and urine samples were obtained at 1-hour and 2-hour intervals, respectively, over a 24-hour period from 10 normotensive and 10 hypertensive pregnant women. VCAM-1 levels were measured by ELISA. Blood pressure was recorded continuously over the 24-hour period. Results: Serum VCAM-1 levels and urinary VCAM-1 excretion were significantly higher in the hypertensive patients than in the controls (851 vs. 659 ng/ml and 62.0 vs. 29.4 pg/min, respectively; P < 0.01). Serum VCAM-1 levels did not show a circadian pattern. In contrast, urinary excretion of VCAM-1 showed a circadian pattern in both groups with a maximum in the daytime hours. There was no correlation with circadian blood pressure variations. Conclusion: Urinary excretion of VCAM-1 shows a circadian pattern in both normotensive and hypertensive pregnancies. Urinary excretion is independent of the serum levels of VCAM-1, which remain stable, and of blood pressure. This suggests intrinsic renal endothelial dysfunction in pregnancies complicated by preeclampsia

Geometry of General Hypersurfaces in Spacetime: Junction Conditions

We study imbedded hypersurfaces in spacetime whose causal character is allowed to change from point to point. Inherited geometrical structures on these hypersurfaces are defined by two methods: first, the standard rigged connection induced by a rigging vector (a vector not tangent to the hypersurface anywhere); and a second, more physically adapted, where each observer in spacetime induces a new type of connection that we call the rigged metric connection. The generalisation of the Gauss and Codazzi equations are also given. With the above machinery, we attack the problem of matching two spacetimes across a general hypersurface. It is seen that the preliminary junction conditions allowing for the correct definition of Einstein's equations in the distributional sense reduce to the requirement that the first fundamental form of the hypersurface be continuous. The Bianchi identities are then proven to hold in the distributional sense. Next, we find the proper junction conditions which forbid the appearance of singular parts in the curvature. Finally, we derive the physical implications of the junction conditions: only six independent discontinuities of the Riemann tensor are allowed. These are six matter discontinuities at non-null points of the hypersurface. For null points, the existence of two arbitrary discontinuities of the Weyl tensor (together with four in the matter tensor) are also allowed.Comment: Latex, no figure

Low-energy dynamics of the γγ→ππ\gamma\gamma\to\pi\pi reaction

We calculate the one-quark-loop amplitude for the low energy $\gamma\gamma\to\pi\pi$ collision in the context of the Nambu and Jona-Lasinio model with scalar and pseudoscalar four quark couplings to all orders in the external momenta. We show that the NJL predictions for the $\gamma\gamma\to\pi^+\pi^-$ reaction are not far from the Born amplitude, which is close to the data, and is compatible with the chiral perturbation theory estimations. We determine the corrections given by the NJL model in leading order of $1/N_c$ to the chiral loop amplitude for $\gamma\gamma\to\pi^0\pi^0$. Numerical results for the $\gamma\gamma\rightarrow\pi\pi$ cross sections and for pion polarizabilities are given.Comment: 20 pages in LaTex, 3 figures in 1 Postscript fil

Meson loop effects in the NJL model at zero and non-zero temperature

We compare two different possibilities to include meson-loop corrections in the Nambu-Jona-Lasinio model: a strict 1/N_c-expansion in next-to-leading order and a non-perturbative scheme corresponding to a one-meson-loop approximation to the effective action. Both schemes are consistent with chiral symmetry, in particular with the Goldstone theorem and the Gell-Mann-Oakes-Renner relation. The numerical part at zero temperature focuses on the pion and the rho-meson sector. For the latter the meson-loop-corrections are crucial in order to include the dominant rho -> pipi-decay channel, while the standard Hartree + RPA approximation only contains unphysical qqbar-decay channels. We find that m_\pi, f_\pi, and quantities related to the rho-meson self-energy can be described reasonably with one parameter set in the 1/N_c-expansion scheme, whereas we did not succeed to obtain such a fit in the non-perturbative scheme. We also investigate the temperature dependence of the quark condensate. Here we find consistency with chiral perturbation theory to lowest order. Similarities and differences of both schemes are discussed.Comment: 51 pages, 18 figures, to be published in Physics of Atomic Nuclei, the volume dedicated to the 90th birthday of A.B. Migdal, error in Eq. 4.22 correcte

Schistosomiasis and malignancy

It is generally accepted that schistosomiasis, if not causative, is at least associated with malignancy. In this review, the epidemiology of schistosomiasis and bladder carcinoma, as well as the role of chronic bladder infection, are discussed togetherwith known carcinogenic factors, possible abnormal vitamin metabolism and/or deficiencies and factors that influence conjugated carcinogens. Experimental evidence is briefly examined and recent work from the Far East on schistosomiasis and colon carcinoma reviewed

Driven Geometric Phase Gates with Trapped Ions

We describe a hybrid laser-microwave scheme to implement two-qubit geometric phase gates in crystals of trapped ions. The proposed gates can attain errors below the fault-tolerance threshold in the presence of thermal, dephasing, laser-phase, and microwave-intensity noise. Moreover, our proposal is technically less demanding than previous schemes, since it does not require a laser arrangement with interferometric stability. The laser beams are tuned close to a single vibrational sideband to entangle the qubits, while strong microwave drivings provide the geometric character to the gate, and thus protect the qubits from these different sources of noise. A thorough analytic and numerical study of the performance of these gates in realistic noisy regimes is presented.Comment: closer to published versio