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

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

Correlated Disorder Substrate‐Integrated Nanodisk Scatterers for Light Extraction in Organic Light Emitting Diodes

A major loss mechanism in organic light emitting diodes (OLEDs) is the coupling of the emitter molecule light field to waveguide modes in the OLED thin film stack. In this work, a disordered 2D array of TiO$_{2}$ nanodisk scatterers is integrated into the OLED substrate to enable efficient light extraction from these waveguide modes. Fabrication of the nanodisks is based on a bottom-up, colloidal lithography technique and subsequent pattern transfer into high refractive index TiO$_{2}$ via reactive ion etching. The substrates are completed by spin-coating a polymer planarization layer before applying the OLED thin film stack. This ensures reproducible optoelectronic properties of the OLED through leaving the electrically active layers planar. Simultaneously, the nanodisks in close vicinity to the thin film stack ensure efficient out-of-plane scattering of waveguide modes. In a monochromatic OLED (center wavelength λ$_{0}$ = 520 nm), a 44.2%$_{rel}$ increase in external quantum efficiency is achieved in comparison to a device without scattering structure. An in-depth numerical analysis reveals that this significant enhancement is only partly due to the out-coupling of waveguide modes. Additional enhancement is suspected to result from out-coupling of substrate modes through scattering by the nanodisks. Further improvements to the scattering structure are numerically evaluated

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