Praseodymium magnetic contribution in the low temperature structure of Pr0.8Ca0.2MnO3

Magnetic and crystal structures of the manganite Pr_0.8Ca_0.2MnO₃ have been studied by neutron powder and single-crystal X-ray diffraction. Structure refinements using single crystal data [orthorhombic system, Pnma, (No. 62), a_RT=5.5534(3) Å, b_RT=7.6548(8) Å, c_RT=5.4400(5) Å, D_x=6.422 g cm⁻³, R^RT=0.029, R_w^RT=0.038] are consistent with a single domain sample. Structure and atomic displacement parameters exclude any electronic localization, even in a disordered way at 300 and 100 K. Low temperature electron diffraction observations do not show any trace of charge ordering.A Pr contribution to the magnetic structure has been shown with a maximum moment of 0.79 μ_B and spins alignments roughly along [101] orientations, at a lower temperature than the ferromagnetic transition observed at 130 K, due to Mn spins ordering.     

Electromagnetic transport properties and magnetoresistance of La0.7Ca0.2Sr0.1MnO3-Ag composites prepared by electroless process

A series of bulk polycrystalline La_0.7Ca_0.2Sr_0.1MnO₃ (LCSMO)-Ag composites were prepared by electroless plating process and several kinds of physical properties have been studied systemically. According to the results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electromagnetic transport properties, we can see that Ag-added segregated at the surfaces or interfaces of LCSMO grains. The metal-insulator transition temperature (T_P) and Curie temperature (T_c) were almost unchanged but ρ decreased with increasing plating time. We also observed Ag-added can significantly enhance the magnetoresistance (MR) near T_P under a low applied field (3000 Oe) and the room temperature MR reached to 35% under 20 kOe, which is encouraging for practical applications. We can suggest that improved grain boundary effect by Ag-added is responsible for the enhancement.     

Magnetic structure determination using polarised resonant X-ray scattering

Full polarisation analysis of resonant X-ray magnetic scattering (RXMS) is shown to advance the determination of magnetic moment directions of complex magnetic structures within single crystals. Key features of this novel method are the variation of the incident beam polarisation through the use of an X-ray phase plate, and the measurement of the scattered beam polarisation in terms of Poincaré-Stokes parameters. Contrary to the established method, no azimuthal rotation is required. Thus, the major sources of systematic error are eliminated, and the method is compatible with exotic and complex sample environments. The technique is demonstrated with the example of TbMn₂O₅. The RXMS theory briefly outlined in this paper was fitted to the data, and the local and delocalized, band-specific moment directions associated with the magnetic order of the resonating species was refined with a high degree of accuracy.     

Double SQUID tunable flux qubit manipulated by fast pulses: operation requirements, dissipation and decoherence

A double SQUID manipulated by fast magnetic flux pulses can be used as a tunable flux qubit. In this paper we study the requirements for the qubit operation and evaluate the dissipation and decoherence due to the manipulation, with particular attention to the contribution related to the applied tuning control, not present in simpler flux qubits. Furthermore, we shortly discuss the possibility to use an integrated Rapid Single Flux Quantum logic for the qubit control.     

Investigation of FIB irradiation damage in La0.7Sr0.3MnO3 thin films

In this work we analyse systematically how morphological and magnetotransport properties of manganite thin films are affected by the damage induced by focused ion beam (FIB) irradiation. We irradiate different areas of the same sample with doses ranging from 5×10¹² to 3×10¹⁷ ions/cm² and we find that the film becomes swollen for doses up to 10¹⁶ ions/cm² and is eventually eroded by ion milling for further irradiation. On the other hand, transport properties are much more sensitive to FIB irradiation: the metal–insulator transition temperature is found to decrease monotonically with increasing doses up to 1.8×10¹³ ions/cm². At doses higher than 5.6×10¹³ ions/cm² the metallic state is completely suppressed and likely, also ferromagnetism.     

A novel nondeterministic scheme for a nondestructive two-qubit controlled phase gate with linear optics

A linear optical scheme for realizing the nondeterministic two-qubit quantum controlled phase gate is presented. The proposed setup involves a pair of product states, polarizing beam splitters, phase shifters and photon number resolving detectors. The omission of entangled ancilla input and additional single-qubit operations significantly reduces the complexity of this gate. This can be well implemented in experiment.     

Thermal entanglement in the anisotropic Heisenberg XYZ model with different inhomogeneous magnetic fields

Thermal entanglement is investigated in a two-qubit Heisenberg XYZ system with different inhomogeneous magnetic fields. It is found that different magnetic fields have different entanglement and critical values. In addition, according to the relation of spin-spin coupling coefficients, a more efficient control parameter of magnetic field can be obtained by adjusting the direction of external magnetic field.     

Magnetic study of phase separation and charge ordering in La1−xSrxMnO3 near x=0.5

We have investigated the magnetic phase diagram of polycrystalline and single-crystal La_1−xSr_xMnO₃ near 0.46≤x≤0.50. It turns out that for x<0.48, the polycrystalline material is ferromagnetic (FM), but for x≥0.48, incipient charge ordering takes place along with antiferromagnetism. At x=0.48, the ferromagnetic-antiferromagnetic phase transition in ceramics occurs at less than 85 kOe but requires significantly larger field for increasing x. These observations are in contrast to what is found in the single crystals, which are all FM.     

Scheme for linear optical preparation of a type of four-photon entangled state with conventional photon detectors

We propose a simple experimental scheme to prepare a type of four-photon entangled state |χ〉 that has many interesting entanglement properties and possible applications in quantum information processing with a certain success probability. The proposed setup involves only simple linear optical devices, a single-photon polarization state, three pairs of two-photon polarization entangled states, and the conventional photon detectors that cannot distinguish a single photon from two or more photons, which greatly simplify the experimental realization of the scheme.