Parity Effect in a Small Superconducting Particle

Matveev and Larkin calculated the parity effect on the ground state energy of a small superconducting particle in the regimes where the mean level spacing is either large or small compared to the bulk gap. We perform a numerical calculation which extends their results into the intermediate regime, where the level spacing is of the same order as the bulk gap.Comment: 6 LaTeX pages, including 2 EPS figures; corrected reference and spellin

Tunneling Anomaly in Superconductor above Paramagnetic Limit

We study the tunneling density of states (DoS) in the superconducting systems driven by Zeeman splitting E_Z into the paramagnetic phase. We show that, even though the BCS gap disappears, superconducting fluctuations cause a strong DoS singularity in the vicinity of energies -E^* for electrons polarized along the magnetic field and E^* for the opposite polarization. The position of the singularity E^*=(1/2) (E_Z + \sqrt{E_Z^2- \Delta^2}) (where \Delta is BCS gap at E_Z=0) is universal. We found analytically the shape of the DoS for different dimensionality of the system. For ultrasmall grains the singularity has the form of the hard gap, while in higher dimensions it appears as a significant though finite dip. Our results are consistent with recent experiments in superconducting films.Comment: 4 pages, 2 .eps figures include

Data and the city – accessibility and openness. a cybersalon paper on open data

This paper showcases examples of bottom–up open data and smart city applications and identifies lessons for future such efforts. Examples include Changify, a neighbourhood-based platform for residents, businesses, and companies; Open Sensors, which provides APIs to help businesses, startups, and individuals develop applications for the Internet of Things; and Cybersalon’s Hackney Treasures. a location-based mobile app that uses Wikipedia entries geolocated in Hackney borough to map notable local residents. Other experiments with sensors and open data by Cybersalon members include Ilze Black and Nanda Khaorapapong's The Breather, a "breathing" balloon that uses high-end, sophisticated sensors to make air quality visible; and James Moulding's AirPublic, which measures pollution levels. Based on Cybersalon's experience to date, getting data to the people is difficult, circuitous, and slow, requiring an intricate process of leadership, public relations, and perseverance. Although there are myriad tools and initiatives, there is no one solution for the actual transfer of that data

Effect of Time Reversal Symmetry Breaking on the Density of States in Small Superconducting Grains

We show that in ultra-small superconducting grains any concentration of magnetic impurities or infinitely small orbital effect of magnetic field leads to destruction of the hard gap in the tunneling density of states. Instead, though exponentially suppressed at low energies, the tunneling density of states exhibits the ``soft gap'' behavior, vanishing linearly with excitation energy, as the energy approaches zero.Comment: 4 pages, 1 eps figur

Hopf algebras and characters of classical groups

Schur functions provide an integral basis of the ring of symmetric functions. It is shown that this ring has a natural Hopf algebra structure by identifying the appropriate product, coproduct, unit, counit and antipode, and their properties. Characters of covariant tensor irreducible representations of the classical groups GL(n), O(n) and Sp(n) are then expressed in terms of Schur functions, and the Hopf algebra is exploited in the determination of group-subgroup branching rules and the decomposition of tensor products. The analysis is carried out in terms of n-independent universal characters. The corresponding rings, CharGL, CharO and CharSp, of universal characters each have their own natural Hopf algebra structure. The appropriate product, coproduct, unit, counit and antipode are identified in each case.Comment: 9 pages. Uses jpconf.cls and jpconf11.clo. Presented by RCK at SSPCM'07, Myczkowce, Poland, Sept 200

Decoherence in qubits due to low-frequency noise

The efficiency of the future devices for quantum information processing is limited mostly by the finite decoherence rates of the qubits. Recently a substantial progress was achieved in enhancing the time, which a solid-state qubit demonstrates a coherent dynamics. This progress is based mostly on a successful isolation of the qubits from external decoherence sources. Under these conditions the material-inherent sources of noise start to play a crucial role. In most cases the noise that quantum device demonstrate has 1/f spectrum. This suggests that the environment that destroys the phase coherence of the qubit can be thought of as a system of two-state fluctuators, which experience random hops between their states. In this short review we discuss the current state of the theory of the decoherence due to the qubit interaction with the fluctuators. We describe the effect of such an environment on different protocols of the qubit manipulations - free induction and echo signal. It turns out that in many important cases the noise produced by the fluctuators is non-Gaussian. Consequently the results of the interaction of the qubit with the fluctuators are not determined by the pair correlation function only. We describe the effect of the fluctuators using so-called spin-fluctuator model. Being quite realistic this model allows one to evaluate the qubit dynamics in the presence of one fluctuator exactly. This solution is found, and its features, including non-Gaussian effects are analyzed in details. We extend this consideration for the systems of large number of fluctuators, which interact with the qubit and lead to the 1/f noise. We discuss existing experiments on the Josephson qubit manipulation and try to identify non-Gaussian behavior.Comment: 25 pages, 7 figure

Solar energy for self-contained power supply

Solar energy relevance in self-contained utility system as well as economic feasibility for each class of consumers considered. The article will outline utilising features of self-contained photovoltaic stations in Middle East and Northern Africa

Non-Gaussian dephasing in flux qubits due to 1/f-noise

Recent experiments by F. Yoshihara et al. [Phys. Rev. Lett. 97, 167001 (2006)] and by K. Kakuyanagi et al. (cond-mat/0609564) provided information on decoherence of the echo signal in Josephson-junction flux qubits at various bias conditions. These results were interpreted assuming a Gaussian model for the decoherence due to 1/f noise. Here we revisit this problem on the basis of the exactly solvable spin-fluctuator model reproducing detailed properties of the 1/f noise interacting with a qubit. We consider the time dependence of the echo signal and conclude that the results based on the Gaussian assumption need essential reconsideration.Comment: Improved fitting parameters, new figur

Observation of Collective-Emission-Induced Cooling inside an Optical Cavity

We report the observation of collective-emission-induced, velocity-dependent light forces. One third of a falling sample containing 3 x 10^6 cesium atoms illuminated by a horizontal standing wave is stopped by cooperatively emitting light into a vertically oriented confocal resonator. We observe decelerations up to 1500 m/s^2 and cooling to temperatures as low as 7 uK, well below the free space Doppler limit. The measured forces substantially exceed those predicted for a single two-level atom.Comment: 10 pages, 5 figure