13 research outputs found
Recoil Polarization for Delta Excitation in Pion Electroproduction
We measured angular distributions of recoil-polarization response functions
for neutral pion electroproduction for W=1.23 GeV at Q^2=1.0 (GeV/c)^2,
obtaining 14 separated response functions plus 2 Rosenbluth combinations; of
these, 12 have been observed for the first time. Dynamical models do not
describe quantities governed by imaginary parts of interference products well,
indicating the need for adjusting magnitudes and phases for nonresonant
amplitudes. We performed a nearly model-independent multipole analysis and
obtained values for Re(S1+/M1+)=-(6.84+/-0.15)% and Re(E1+/M1+)=-(2.91+/-0.19)%
that are distinctly different from those from the traditional Legendre analysis
based upon M1+ dominance and sp truncation.Comment: 5 pages, 2 figures, for PR
Recoil polarization measurements for neutral pion electroproduction at Q2=1(GeV/c)2 near the Δ resonance
We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q2=1.0(GeV/c)2 in 10 bins of 1.17≤W≤1.35 GeV across the Δ resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near the physical mass, W=MΔ1.232 GeV, but the variation among models is large for response functions governed by imaginary parts, and for both types of response functions, the variation increases rapidly with W>MΔ. We performed a multipole analysis that adjusts suitable subsets of π≤2 amplitudes with higher partial waves constrained by baseline models. This analysis provides both real and imaginary parts. The fitted multipole amplitudes are nearly model independent-there is very little sensitivity to the choice of baseline model or truncation scheme. By contrast, truncation errors in the traditional Legendre analysis of N→Δ quadrupole ratios are not negligible. Parabolic fits to the W dependence around MΔ for the multiple analysis gives values for Re(S1+/M1+)=(-6.61±0. 18)% and Re(E1+/M1+)=(-2.87±0.19)% for the pπ0 channel at W=1.232 GeV and Q2=1.0(GeV/c)2 that are distinctly larger than those from the Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S0+/M1+)=(+7.1±0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe. © 2007 The American Physical Society
Photonic spatial Bell-state analysis for robust quantum secure direct communication using quantum dot-cavity systems
Recently, experiments showed that the spatial-mode states of entangled
photons are more robust than their polarization-mode states in quantum
communications. Here we construct a complete and deterministic protocol for
analyzing the spatial Bell states using the interaction between a photon and an
electron spin in a charged quantum dot inside a one-side micropillar
microcavity. A quantum nondemolition detector (QND) for checking the parity of
a two-photon system can be constructed with the giant optical Faraday rotation
in this solid state system. With this parity-check QND, we present a complete
and deterministic proposal for the analysis of the four spatial-mode Bell
states. Moreover, we present a robust two-step quantum secure direct
communication protocol based on the spatial-mode Bell states and the photonic
spatial Bell-state analysis. Our analysis shows that our BSA proposal works in
both the strong and the weak coupling regimes if the side leakage and cavity
loss rate is small.Comment: 8 pages, 4 figure