Entanglement in quantum XY spin chains of arbitrary length is investigated via a recentlydeveloped global measure suitable for generic quantum many-body systems. The entanglement surface is determined over the phase diagram, and found to exhibit structure richer than expected. Near the critical line, the entanglement is peaked (albeit analytically), consistent with the notion that entanglement-the non-factorization of wave functions-reflects quantum correlations. Singularity does, however, accompany the critical line, as revealed by the divergence of the field-derivative of the entanglement along the line. The form of this singularity is dictated by the universality class controlling the quantum phase transition. [5,6,7,8], where it can play the role of a diagnostic of quantum correlations. Quantum phase transitions [9] are transitions between qualitatively distinct phases of quantum many-body systems, driven by quantum fluctuations. In view of the connection between entanglement and quantum correlations, one anticipates that entanglement will furnish a dramatic signature of the quantum critical point. From the viewpoint of quantum information, the more entangled a state, the more resources it is likely to possess. It is thus desirable to study and quantify the degree of entanglement near quantum phase transitions. By employing entanglement to diagnose many-body quantum states one may obtain fresh insight into the quantum many-body problem.To date, progress in quantifying entanglement has taken place primarily in the domain of bipartite systems [10]. Much of the previous work on entanglement in quantum phase transitions has been based on bipartite measures, i.e., focus has been on entanglement either between pairs of parties [5,6] or between a part and the remainder of a system [7]. For multipartite systems, however, the complete characterization of entanglement requires the consideration of multipartite entanglement, for which a consensus measure has not yet emerged.Singular and scaling behavior of entanglement near quantum critical points was discovered in important work by Osterloh and co-workers [6], who invoked Wootters' bipartite concurrence [11] as a measure of entanglement. In the present letter, we apply a recently-developed global measure that provides a holistic, rather than bipartite, characterization of the entanglement of quantum manybody systems. Our focus is on one-dimensional spin systems, specifically ones that are exactly solvable and

Recently, lead free all-inorganic double perovskites have revolutionized photovoltaic research, showing promising light emitting efficiency and tunability via modification of inherent structural and chemical properties. Here, we report a combined experimental and theoretical study on the variation of carrier–lattice interaction and optoelectronic properties of Cs2AgIn1–x Bi x Cl6 double perovskite nanocrystals with varying alloying concentrations. Our UV–vis study confirms the parity allowed first direct transition for x ≤ 0.25. Using a careful analysis of Raman spectra assisted with first-principles simulations, we assign the possible three types of active modes to intrinsic atomic vibrations; 2 T2g modes (one for translational motion of “Cs” and other for octahedral breathing), 1 Eg and 1 A1g mode for various stretching of Ag–Cl octahedra. Ab-initio simulation reveals dominant carrier-phonon scattering via Fröhlich mechanism near room temperature, with longitudinal optical phonons being effectively activated around 230 K. We observe a noticeable increase in hole mobility (∼4 times) with small Bi alloying, attributed to valence band (VB) maxima acquiring Bi-s orbital characteristics, thus resulting in a dispersive VB. We believe that our results should help to gain a better understanding of the intrinsic electronic and lattice dynamical properties of these compounds and provide a base toward improving the overall performance of double perovskite nanocrystals.

We study the macroscopic entanglement properties of a lowdimensional quantum spin system by investigating its magnetic properties at low temperatures and high magnetic fields. The spin system chosen for this is copper nitrate (Cu(NO 3 ) 2 × 2.5H 2 O), which is a spin chain that exhibits dimerization. The temperature and magnetic field dependence of entanglement from the susceptibility and magnetization data are given, by comparing the experimental results with the theoretical estimates. Extraction of entanglement has been made possible through the macroscopic witness operator, magnetic susceptibility. An explicit comparison of the experimental extraction of entanglement with theoretical estimates is provided. It was found that theory and experiments match over a wide range of temperatures and fields. The spin system studied exhibits quantum phase transition (QPT) at low temperatures when the magnetic field is swept through a critical value. We show explicitly for the first time, using tools used in quantum information processing, that QPT can be captured experimentally using quantum complementary observables, which clearly delineate entangled states from separable ones across the QPT.

We have synthesized La0.67Ca0.33MnO3 (LCMO):xZnO () composites through a citrate gel route and have characterized them for magnetic and magnetotransport properties. In lower concentrations (), ZnO mostly goes into the perovskite lattice substituting Mn in LCMO and segregates less in the grain boundary region, but at higher concentration (x>0.13) it segregates mostly at the grain boundaries of LCMO and influences the transport properties significantly. A model is proposed which describes the overall resistivity of the system as a parallel combination of a low resistive intragrain conducting path and a high resistive intergrain insulating path. Using this approach, the grain and grain boundary contributions to the overall resistivity are separated for all the composites. The field dependent resistivity shows that all the composites have higher values of MR at the transition temperatures (TMI) compared to that in pure LCMO (x = 0). The highest value of MR is obtained for x = 0.10 and is 76.6% at 80 kOe field near TMI.

The composites of La 2=3 Ca 1=3 MnO 3 :xSiO 2 (0pxp0:40) have been synthesized by sol-gel technique to derive homogeneous nanocomposites. Si 4þ by virtue of its strong preference for tetrahedral site does not enter the perovskite lattice. The percolation threshold composition has been determined by resistivity measurements at around 90% volume fraction of LCMO. A detailed electrical, magnetic and magneto-transport characterizations have been carried out for composites around the threshold composition (x ¼ 0:05; 0:10; 0:15). The magnetoresistance results at 1 T show a sharp peak at T c and a minimum just below T c as reported in several polycrystalline LCMO composites.

Magnetic properties of isotropic Sm-Fe-N magnets produced by compression shearing method J. Appl. Phys. 111, 07A716 (2012) Stable vortex magnetite nanorings colloid: Micromagnetic simulation and experimental demonstration J. Appl. Phys. 111, 044303 (2012) Evidence for low temperature glassy behavior in La0.5Sr0.5CoO3 J. Appl. Phys. 111, 043902 (2012) Temperature dependent phonon Raman scattering of highly a-axis oriented CoFe2O4 inverse spinel ferromagnetic films grown by pulsed laser deposition Appl. Phys. Lett. 100, 071905 (2012) Additional information on J. Appl. Phys.

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We experimentally demonstrate the localization of excitation between hyperfine ground states of 87 Rb atoms to as small as λ/13 wide spatial regions. We use ultracold atoms trapped in a dipole trap and utilize electromagnetically induced transparency (EIT) for the atomic excitation.The localization is achieved by combining a spatially varying coupling laser (standing-wave) with the intensity dependence of EIT. The excitation is fast (150 ns laser pulses) and the dark-state fidelity can be made higher than 94% throughout the standing wave. Because the width of the localized regions is much smaller than the wavelength of the driving light, traditional optical imaging techniques cannot resolve the localized features. Therefore, to measure the excitation profile, we use an auto-correlation-like method where we perform two EIT sequences separated by a time delay, during which we move the standing wave. 1 I. 1. INTRODUCTIONThe diffraction limit, which posits that traditional optical techniques cannot resolve or write features smaller than about half the wavelength of light, is an important barrier for a variety of research areas. For example, a number of quantum computing implementations, such as those utilizing trapped neutral atoms, use focused laser beams to trap, initialize, and manipulate qubits [1][2][3][4][5]. In a neutral-atom quantum computing architecture, the qubit spacing has to be larger than half the wavelength, which limits the two-qubit interaction energies that can be obtained (for example through Rydberg dipole-dipole interaction). The necessary qubit spacing in turn limits the fidelity and the speed of the two-qubit gates. A technique to address atoms with high fidelity in sub-wavelength spatial scales would greatly improve the performance of the two-qubit gates. In this work, we use the dark state of electromagnetically induced transparency (EIT) [6][7][8][9] to address atoms in regions much smaller than the diffraction limit. We use a standing wave coupling laser and demonstrate efficient transfer between the ground levels of 87 Rb in regions with widths as small as λ/13. The transfer is fast (150 ns laser pulses) and the fidelity for the atomic system to be in the dark state can be made higher than 94% at all spatial points along the standing wave. We perform these experiments using ultracold 87 Rb atoms trapped in a far-off-resonant dipole trap at a temperature of ≈ 1 µK. Although other techniques have been investigated that achieve sub-wavelength resolution, using the dark state provides key advantages for quantum computing. The atoms are coherently transferred [9], keeping their phase relationship with other qubits intact. The dark state can be prepared with little population transfer to a radiative excited state, which reduces heating and decoherence from spontaneous emission.Because the excitation is coherent, dark-state based localization can be achieved using short and intense laser pulses, allowing fast quantum gates to be constructed.There has been other important work related to address...