New Samarium and Neodymium based admixed ferromagnets with near zero net magnetization and tunable exchange bias field

Rare earth based intermetallics, SmScGe and NdScGe, are shown to exhibit near zero net magnetization with substitutions of 6 to 9 atomic percent of Nd and 25 atomic percent of Gd, respectively. The notion of magnetic compensation in them is also elucidated by the crossover of zero magnetization axis at low magnetic fields (less than 103 Oe) and field-induced reversal in the orientation of the magnetic moments of the dissimilar rare earth ions at higher magnetic fields. These magnetically ordered materials with no net magnetization and appreciable conduction electron polarization display an attribute of an exchange bias field, which can be tuned. The attractively high magnetic ordering temperatures of about 270 K, underscore the importance of these materials for potential applications in spintronics.Comment: 6 page text + 5 figure

New summing algorithm using ensemble computing

We propose an ensemble algorithm, which provides a new approach for evaluating and summing up a set of function samples. The proposed algorithm is not a quantum algorithm, insofar it does not involve quantum entanglement. The query complexity of the algorithm depends only on the scaling of the measurement sensitivity with the number of distinct spin sub-ensembles. From a practical point of view, the proposed algorithm may result in an exponential speedup, compared to known quantum and classical summing algorithms. However in general, this advantage exists only if the total number of function samples is below a threshold value which depends on the measurement sensitivity.Comment: 13 pages, 0 figures, VIth International Conference on Quantum Communication, Measurement and Computing (Boston, 2002

Numerical simulation of a Controlled-Controlled-Not (CCN) quantum gate in a chain of three interacting nuclear spins system

We present the study of a quantum Controlled-Controlled-Not gate, implemented in a chain of three nuclear spins weakly Ising interacting between all of them, that is, taking into account first and second neighbor spin interactions. This implementation is done using a single resonant $\pi$-pulse on the initial state of the system (digital and superposition). The fidelity parameter is used to determine the behavior of the CCN quantum gate as a function of the ratio of the second neighbor interaction coupling constant to the first neighbor interaction coupling constant ($J'/J$). We found that for $J'/J\ge 0.02$ we can have a well defined CCN quantum gate.Comment: 9 pages, 5 fugure

Entangling capacity of global phases and implications for Deutsch-Jozsa algorithm

We investigate the creation of entanglement by the application of phases whose value depends on the state of a collection of qubits. First we give the necessary and sufficient conditions for a given set of phases to result in the creation of entanglement in a state comprising of an arbitrary number of qubits. Then we analyze the creation of entanglement between any two qubits in three qubit pure and mixed states. We use our result to prove that entanglement is necessary for Deutsch-Jozsa algorithm to have an exponential advantage over its classical counterpart.Comment: All 8 figures at the en

Reentrant Peak Effect in an anisotropic superconductor 2H-NbSe_2 : Role of disorder

The reentrant nature of Peak Effect is established in a single crystal of 2H-NbSe_2 via electrical transport and dc magnetisation studies. The role of disorder on the reentrant branch of PE has been examined in three single crystals with varying levels of quenched random disorder. Increasing disorder presumably shrinks the (H,T) parameter space over which vortex array retains spatial order. Although, the upper branch of the PE curve is somewhat robust, the lower reentrant branch of the same curve is strongly affected by disorder.Comment: 5 Pages of text, 4 figure

The elusive source of quantum effectiveness

We discuss two qualities of quantum systems: various correlations existing between their subsystems and the distingushability of different quantum states. This is then applied to analysing quantum information processing. While quantum correlations, or entanglement, are clearly of paramount importance for efficient pure state manipulations, mixed states present a much richer arena and reveal a more subtle interplay between correlations and distinguishability. The current work explores a number of issues related with identifying the important ingredients needed for quantum information processing. We discuss the Deutsch-Jozsa algorithm, the Shor algorithm, the Grover algorithm and the power of a single qubit class of algorithms. One section is dedicated to cluster states where entanglement is crucial, but its precise role is highly counter-intuitive. Here we see that distinguishability becomes a more useful concept.Comment: 8 pages, no figure

Quantum heuristic algorithm for traveling salesman problem

We propose a quantum heuristic algorithm to solve a traveling salesman problem by generalizing Grover search. Sufficient conditions are derived to greatly enhance the probability of finding the tours with extremal costs, reaching almost to unity and they are shown characterized by statistical properties of tour costs. In particular for a Gaussian distribution of the tours along the cost we show that the quantum algorithm exhibits the quadratic speedup of its classical counterpart, similarly to Grover search.Comment: Published versio

Magnetization hysteresis and time decay measurements in FeSe0.50_{0.50}Te0.50_{0.50} : Evidence for fluctuation in mean free path induced pinning

We present results of magnetic measurements relating to vortex phase diagram in a single crystal of FeSe$_{0.5}$Te$_{0.5}$ which displays second magnetization peak anomaly for $H \parallel c$. The possible role of the crystalline anisotropy on vortex pinning is explored via magnetic torque magnetometry. We present evidence in favor of pinning related to spatial variations of the charge carrier mean free path leading to small bundle vortex pinning by randomly distributed (weak) pinning centers for both $H \parallel c$ and $H \perp c$. This is further corroborated using magnetization data for $H \parallel c$ in a single crystal of FeSe$_{0.35}$Te$_{0.65}$. Dynamical response across second magnetization peak (SMP) anomaly in FeSe$_{0.5}$Te$_{0.5}$ has been compared with that across the well researched phenomenon of peak effect (PE) in a single crystal of CeRu$_2$.Comment: 11 figures, provided additional data in another sample, added Fig.

A theory of metamaterials based on periodically loaded transmission lines: Interaction between magnetoinductive and electromagnetic waves

Published versio