Nonequilibrium collective phenomena in the onset of pitting corrosion

Nonequilibrium collective phenomena and effects of nonlinear pattern formation play the crucial role in the onset of pitting corrosion on stainless steels. Such materials are naturally protected by the oxide layer covering their surface. The onset of pitting corrosion involves the development of microscopic metastable pits, each persisting for about a second. As proposed in our publications and confirmed in subsequent experiments, sudden transition to active corrosion results from chain reproduction of metastable pits on the stainless steel surface leading to an autocatalytic explosion

Optical vortices of slow light using tripod scheme

We consider propagation, storing and retrieval of slow light (probe beam) in a resonant atomic medium illuminated by two control laser beams of larger intensity. The probe and two control beams act on atoms in a tripod configuration of the light-matter coupling. The first control beam is allowed to have an orbital angular momentum (OAM). Application of the second vortex-free control laser ensures the adiabatic (lossles) propagation of the probe beam at the vortex core where the intensity of the first control laser goes to zero. Storing and release of the probe beam is accomplished by switching off and on the control laser beams leading to the transfer of the optical vortex from the first control beam to the regenerated probe field. A part of the stored probe beam remains frozen in the medium in the form of atomic spin excitations, the number of which increases with increasing the intensity of the second control laser. We analyse such losses in the regenerated probe beam and provide conditions for the optical vortex of the control beam to be transferred efficiently to the restored probe beam.Comment: 2 figure

A Bayesian Estimate of the Primordial Helium Abundance

We introduce a new statistical method to estimate the primordial helium abundance, Y_p from observed abundances in a sample of galaxies which have experienced stellar helium enrichment. Rather than using linear regression on metal abundance we construct a likelihood function using a Bayesian prior, where the key assumption is that the true helium abundance must always exceed the primordial value. Using a sample of measurements compiled from the literature we find estimates of Y_p between 0.221 and 0.236, depending on the specific subsample and prior adopted, consistent with previous estimates either from a linear extrapolation of the helium abundance with respect to metallicity, or from the helium abundance of the lowest metallicity HII region, I Zw 18. We also find an upper limit which is insensitive to the specific subsample or prior, and estimate a model-independent bound Y_p < 0.243 at 95% confidence, favoring a low cosmic baryon density and a high primordial deuterium abundance. The main uncertainty is not the model of stellar enrichment but possible common systematic biases in the estimate of Y in each individual HII region.Comment: 14 pages, latex, 3 ps figure

Slow polaritons with orbital angular momentum in atomic gases

Polariton formalism is applied for studying the propagation of a probe field of light in a cloud of cold atoms influenced by two control laser beams of larger intensity. The laser beams couple resonantly three hyperfine atomic ground states to a common excited state thus forming a tripod configuration of the atomic energy levels involved. The first control beam can have an optical vortex with the intensity of the beam going to zero at the vortex core. The second control beam without a vortex ensures the loseless (adiabatic) propagation of the probe beam at a vortex core of the first control laser. We investigate the storage of the probe pulse into atomic coherences by switching off the control beams, as well as its subsequent retrieval by switching the control beams on. The optical vortex is transferred from the control to the probe fields during the storage or retrieval of the probe field. We analyze conditions for the vortex to be transferred efficiently to the regenerated probe beam and discuss possibilities of experimental implementation of the proposed scheme using atoms like rubidium or sodium.Comment: 4 figure

Electromagnetically induced transparency on a single artificial atom

We present experimental observation of electromagnetically induced transparency (EIT) on a single macroscopic artificial "atom" (superconducting quantum system) coupled to open 1D space of a transmission line. Unlike in a optical media with many atoms, the single atom EIT in 1D space is revealed in suppression of reflection of electromagnetic waves, rather than absorption. The observed almost 100 % modulation of the reflection and transmission of propagating microwaves demonstrates full controllability of individual artificial atoms and a possibility to manipulate the atomic states. The system can be used as a switchable mirror of microwaves and opens a good perspective for its applications in photonic quantum information processing and other fields

Counting statistics of interfering Bose-Einstein condensates

A method is presented that is able to predict the probability of outcomes of snapshot measurements, such as the images of the instantaneous particle density distribution in a quantum many-body system. It is shown that a gauge-like transformation of the phase of the many-body wave function allows one to construct a probability generating functional, the Fourier transform of which with respect to the "gauge" field returns the joint probability distribution to detect any given number of particles at various locations. The method is applied to the problem of interference of two independent clouds of Bose-Einstein condensates, where the initially separated clouds with fixed boson numbers expand and the density profile image of the overlapping clouds is registered. In the limit of large particle numbers, the probability to observe a particular image of the density profile is shown to be given by a sum of partial probability distributions, each of which corresponds to a noisy image of interference of two matter waves with definite phase difference. In agreement with earlier theoretical arguments, interference fringes are, therefore, expected in any single shot measurement, the fringe pattern randomly varying from run to run. These results conform to the physical picture where the Bose-Einstein clouds are in spontaneously symmetry broken states, the hidden phases of which are revealed by the density profile measurement via the position of the interference fringes.Comment: Some changes in presentation, as published, 6 pages, LaTe

Entangling photons via the double quantum Zeno effect

We propose a scheme for entangling two photons via the quantum Zeno effect, which describes the inhibition of quantum evolution by frequent measurements and is based on the difference between summing amplitudes and probabilities. For a given error probability $P_{\rm error}$, our scheme requires that the one-photon loss rate $\xi_{1\gamma}$ and the two-photon absorption rate $\xi_{2\gamma}$ in some medium satisfy $\xi_{1\gamma}/\xi_{2\gamma}=2P_{\rm error}^2/\pi^2$, which is significantly improved in comparison to previous approaches. Again based on the quantum Zeno effect, as well as coherent excitations, we present a possibility to fulfill this requirement in an otherwise linear optics set-up.Comment: 4 pages RevTeX, 2 figure

The second law, Maxwell's daemon and work derivable from quantum heat engines

With a class of quantum heat engines which consists of two-energy-eigenstate systems undergoing, respectively, quantum adiabatic processes and energy exchanges with heat baths at different stages of a cycle, we are able to clarify some important aspects of the second law of thermodynamics. The quantum heat engines also offer a practical way, as an alternative to Szilard's engine, to physically realise Maxwell's daemon. While respecting the second law on the average, they are also capable of extracting more work from the heat baths than is otherwise possible in thermal equilibrium

Photonic band-gap properties for two-component slow light

We consider two-component "spinor" slow light in an ensemble of atoms coherently driven by two pairs of counterpropagating control laser fields in a double tripod-type linkage scheme. We derive an equation of motion for the spinor slow light (SSL) representing an effective Dirac equation for a massive particle with the mass determined by the two-photon detuning. By changing the detuning the atomic medium acts as a photonic crystal with a controllable band gap. If the frequency of the incident probe light lies within the band gap, the light tunnels through the sample. For frequencies outside the band gap, the transmission probability oscillates with increasing length of the sample. In both cases the reflection takes place into the complementary mode of the probe field. We investigate the influence of the finite excited state lifetime on the transmission and reflection coefficients of the probe light. We discuss possible experimental implementations of the SSL using alkali atoms such as Rubidium or Sodium.Comment: 7 figure

Controlled light storage in a double lambda system

It is shown theoretically that after light storing in a medium of four-level atoms it is possible to release a new pulse of a different frequency, the process being steered by another driving beam. It is also possible to store one pulse and to release two different ones, with their time separation and heights being controlled.Comment: 7 pages,3 figure