Direct determination of the spin structure of Nd2_2Ir2_2O7_7 by means of neutron diffraction

We report on the spin structure of the pyrochlore iridate Nd$_2$Ir$_2$O$_7$ that could be directly determined by means of powder neutron diffraction. Our magnetic structure refinement unravels a so-called all-in/all-out magnetic structure that appears in both, the Nd and the Ir sublattice. The ordered magnetic moments at 1.8 K amount to 0.34(1) $\mu_\mathrm{B}$/Ir$^{4+}$ and 1.27(1) $\mu_\mathrm{B}$/Nd$^{3+}$. The Nd$^{3+}$ moment size at 1.8 K is smaller than that expected for the Nd$^{3+}$ ground state doublet. On the other hand, the size of the ordered moments of the Ir$^{4+}$ ions at 1.8 K agrees very well with the value expected for a $J_\mathrm{eff}$ = 1/2 state based on the presence of strong spin-orbit coupling in this system. Finally, our measurements reveal a parallel alignment of the Nd$^{3+}$ moments with the net moment of its six nearest neighboring Ir$^{4+}$ ions.Comment: http://journals.aps.org/prb/pdf/10.1103/PhysRevB.94.16110

Systematic {\it ab initio} study of the magnetic and electronic properties of all 3d transition metal linear and zigzag nanowires

It is found that all the zigzag chains except the nonmagnetic (NM) Ni and antiferromagnetic (AF) Fe chains which form a twisted two-legger ladder, look like a corner-sharing triangle ribbon, and have a lower total energy than the corresponding linear chains. All the 3d transition metals in both linear and zigzag structures have a stable or metastable ferromagnetic (FM) state. The electronic spin-polarization at the Fermi level in the FM Sc, V, Mn, Fe, Co and Ni linear chains is close to 90% or above. In the zigzag structure, the AF state is more stable than the FM state only in the Cr chain. It is found that the shape anisotropy energy may be comparable to the electronic one and always prefers the axial magnetization in both the linear and zigzag structures. In the zigzag chains, there is also a pronounced shape anisotropy in the plane perpendicular to the chain axis. Remarkably, the axial magnetic anisotropy in the FM Ni linear chain is gigantic, being ~12 meV/atom. Interestingly, there is a spin-reorientation transition in the FM Fe and Co linear chains when the chains are compressed or elongated. Large orbital magnetic moment is found in the FM Fe, Co and Ni linear chains

Direct X(3872) production in e+e- collisions

Direct production of the charmonium-like state $X(3872)$ in $e^+e^-$ collisions is considered in the framework of the vector meson dominance model. An order-of-magnitude estimate for the width $\Gamma(X\to e^+e^-)$ is found to be $\gtrsim$0.03 eV. The same approach applied to the $\chi_{c1}$ charmonium decay predicts the corresponding width of the order 0.1 eV in agreement with earlier estimates. Experimental perspectives for the direct production of the $1^{++}$ charmonia in $e^+e^-$ collisions are briefly discussed.Comment: LaTeX2e, 11 pages, 1 figure, version published in Phys.Lett.

A Storage-Efficient and Robust Private Information Retrieval Scheme Allowing Few Servers

Since the concept of locally decodable codes was introduced by Katz and Trevisan in 2000, it is well-known that information the-oretically secure private information retrieval schemes can be built using locally decodable codes. In this paper, we construct a Byzantine ro-bust PIR scheme using the multiplicity codes introduced by Kopparty et al. Our main contributions are on the one hand to avoid full replica-tion of the database on each server; this significantly reduces the global redundancy. On the other hand, to have a much lower locality in the PIR context than in the LDC context. This shows that there exists two different notions: LDC-locality and PIR-locality. This is made possible by exploiting geometric properties of multiplicity codes

Generation of a High-Visibility Four-Photon Entangled State and Realization of a Four-Party Quantum Communication Complexity Scenario

We obtain a four-photon polarization-entangled state with a visibility as high as (95.35\pm 0.45)% directly from a single down-conversion source. A success probability of (81.54\pm 1.38)% is observed by applying this entangled state to realize a four-party quantum communication complexity scenario (QCCS), which comfortably surpass the classical limit of 50%. As a comparison, two Einstein-Podolsky-Rosen (EPR) pairs are shown to implement the scenario with a success probability of (73.89\pm 1.33)%. This four-photon state can be used to fulfill decoherence-free quantum information processing and other advanced quantum communication schemes.Comment: REVTEX 4.0, 4 pages, 4 figures, 1 tabl

Plasmon assisted transmission of high dimensional orbital angular momentum entangled state

We present an experimental evidence that high dimensional orbital angular momentum entanglement of a pair of photons can be survived after a photon-plasmon-photon conversion. The information of spatial modes can be coherently transmitted by surface plasmons. This experiment primarily studies the high dimensional entangled systems based on surface plasmon with subwavelength structures. It maybe useful in the investigation of spatial mode properties of surface plasmon assisted transmission through subwavelength hole arrays.Comment: 7 pages,6 figure

Optimal nonlocal multipartite entanglement concentration based on projection measurements

We propose an optimal nonlocal entanglement concentration protocol (ECP) for multi-photon systems in a partially entangled pure state, resorting to the projection measurement on an additional photon. One party in quantum communication first performs a parity-check measurement on her photon in an N-photon system and an additional photon, and then she projects the additional photon into an orthogonal Hilbert space for dividing the original $N$-photon systems into two groups. In the first group, the N parties will obtain a subset of $N$-photon systems in a maximally entangled state. In the second group, they will obtain some less-entangled N-photon systems which are the resource for the entanglement concentration in the next round. By iterating the entanglement concentration process several times, the present ECP has the maximal success probability which is just equivalent to the entanglement of the partially entangled state. That is, this ECP is an optimal one.Comment: 5 pages, 4 figure

Modulation of Neurally Mediated Vasodepression and Bradycardia by Electroacupuncture through Opioids in Nucleus Tractus Solitarius.

Stimulation of vagal afferent endings with intravenous phenylbiguanide (PBG) causes both bradycardia and vasodepression, simulating neurally mediated syncope. Activation of µ-opioid receptors in the nucleus tractus solitarius (NTS) increases blood pressure. Electroacupuncture (EA) stimulation of somatosensory nerves underneath acupoints P5-6, ST36-37, LI6-7 or G37-39 selectively but differentially modulates sympathoexcitatory responses. We therefore hypothesized that EA-stimulation at P5-6 or ST36-37, but not LI6-7 or G37-39 acupoints, inhibits the bradycardia and vasodepression through a µ-opioid receptor mechanism in the NTS. We observed that stimulation at acupoints P5-6 and ST36-37 overlying the deep somatosensory nerves and LI6-7 and G37-39 overlying cutaneous nerves differentially evoked NTS neural activity in anesthetized and ventilated animals. Thirty-min of EA-stimulation at P5-6 or ST36-37 reduced the depressor and bradycardia responses to PBG while EA at LI6-7 or G37-39 did not. Congruent with the hemodynamic responses, EA at P5-6 and ST36-37, but not at LI6-7 and G37-39, reduced vagally evoked activity of cardiovascular NTS cells. Finally, opioid receptor blockade in the NTS with naloxone or a specific μ-receptor antagonist reversed P5-6 EA-inhibition of the depressor, bradycardia and vagally evoked NTS activity. These data suggest that point specific EA stimulation inhibits PBG-induced vasodepression and bradycardia responses through a μ-opioid mechanism in the NTS

Efficient multipartite entanglement purification with the entanglement link from a subspace

We present an efficient multipartite entanglement purification protocol (MEPP) for N-photon systems in a Greenberger-Horne-Zeilinger state with parity-check detectors. It contains two parts. One is the conventional MEPP with which the parties can obtain a high-fidelity N-photon ensemble directly, similar to the MEPP with controlled-not gates. The other is our recycling MEPP in which the entanglement link is used to produce some $N$-photon entangled systems from entangled N'-photon subsystems (2 \leq N'<N) coming from the instances which are just discarded in all existing conventional MEPPs. The entangled N'-photon subsystems are obtained efficiently by measuring the photons with potential bit-flip errors. With these two parts, the present MEPP has a higher efficiency than all other conventional MEPPs.Comment: 17 pages, 9 figures, 2 tables. We correct the error in the address of the author in the published version (Phys. Rev. A 84, 052312 (2011)