26,160 research outputs found
Experimental implementation of high-fidelity unconventional geometric quantum gates using NMR interferometer
Following a key idea of unconventional geometric quantum computation
developed earlier [Phys. Rev. Lett. 91, 197902 (2003)], here we propose a more
general scheme in such an intriguing way: , where and are respectively the dynamic and
geometric phases accumulated in the quantum gate operation, with as a
constant and being dependent only on the geometric feature of the
operation. More arrestingly, we demonstrate the first experiment to implement a
universal set of such kind of generalized unconventional geometric quantum
gates with high fidelity in an NMR system.Comment: 4 pages, 3 figure
Entanglement of separate nitrogen-vacancy centers coupled to a whispering-gallery mode cavity
We present a quantum electrodynamical model involving nitrogen-vacancy
centers coupled to a whispering-gallery mode cavity. Two schemes are considered
to create W state and Bell state, respectively. One of the schemes makes use of
the Raman transition with the cavity field virtually excited; The other enables
the Bell state preparation and quantum information transfer by virtue of dark
state evolution and adiabatic passage, which is tolerant to ambient noise and
experimental parameter fluctuations. We justify our schemes by considering the
experimental feasibility and challenge using currently available technology.Comment: 8 pages and 5 figure
Microwave photoresistance of a high-mobility two-dimensional electron gas in a triangular antidot lattice
The microwave (MW) photoresistance has been measured on a high-mobility
two-dimensional electron gas patterned with a shallow triangular antidot
lattice, where both the MW-induced resistance oscillations (MIRO) and
magnetoplasmon (MP) resonance are observed superposing on sharp commensurate
geometrical resonance (GR). Analysis shows that the MIRO, MP, and GR are
decoupled from each other in these experiments.Comment: 5 pages, 4 figures, paper accepted by PR
Photovoltaic Oscillations Due to Edge-Magnetoplasmon Modes in a Very-High Mobility 2D Electron Gas
Using very-high mobility GaAs/AlGaAs 2D electron Hall bar samples, we have
experimentally studied the photoresistance/photovoltaic oscillations induced by
microwave irradiation in the regime where both 1/B and B-periodic oscillations
can be observed. In the frequency range between 27 and 130 GHz we found that
these two types of oscillations are decoupled from each other, consistent with
the respective models that 1/B oscillations occur in bulk while the
B-oscillations occur along the edges of the Hall bars. In contrast to the
original report of this phenomenon (Ref. 1) the periodicity of the
B-oscillations in our samples are found to be independent of L, the length of
the Hall bar section between voltage measuring leads.Comment: 4 pages, 4 figure
Testing mechanisms of compensatory fitness of dioecy in a cosexual world
Questions: All else being equal, populations of dioecious species with a 50:50 sex ratio have only half the effective reproductive population size of bisexual species of equal abundance. Consequently, there is a need to explain how dioecious and bisexual species coexist. Increased mean individual seed mass, fecundity, and population density have all been proposed as attributes of unisexual individuals or populations that may contribute to the persistence or resilience of dioecious species. To date, no studies have compared sympatric dioecious and cosexual species with respect to all three components of fitness. In this study, we sought evidence for these compensatory advantages (higher seed mass, greater seed production per unit basal area, and higher population density) in dioecious species. Location: Five 20–25 ha forest dynamic plots spanning a latitudinal gradient in China, including two temperate, two subtropical, and one tropical forest. Methods: We used a phylogenetically corrected generalized linear modelling approach to assess the phylogenetic dependence and joint evolution of sexual system, seed mass and production, and ecological abundances among 48–333 species and 32,568–136,237 individuals per forest. Results: Across all five forests, we detected no consistent advantage for dioecious relative to sympatric cosexual species with respect to mean individual seed mass, seed production or the density of stems in any size class. Conclusions: Our study suggests that seed traits may provide compensatory mechanisms in some forests, but most often the coexistence of sexual systems cannot be explained by advantages of dioecy related to seed quality and demographic parameters. Future investigations of the factors that promote coexistence may increase our understanding by expanding the search to include attributes such as lifespan and tolerance or resistance to herbivores
Predicting the solar maximum with the rising rate
The growth rate of solar activity in the early phase of a solar cycle has
been known to be well correlated with the subsequent amplitude (solar maximum).
It provides very useful information for a new solar cycle as its variation
reflects the temporal evolution of the dynamic process of solar magnetic
activities from the initial phase to the peak phase of the cycle. The
correlation coefficient between the solar maximum (Rmax) and the rising rate
({\beta}a) at {\Delta}m months after the solar minimum (Rmin) is studied and
shown to increase as the cycle progresses with an inflection point (r = 0.83)
at about {\Delta}m = 20 months. The prediction error of Rmax based on {\beta}a
is found within estimation at the 90% level of confidence and the relative
prediction error will be less than 20% when {\Delta}m \geq 20. From the above
relationship, the current cycle (24) is preliminarily predicted to peak around
October 2013 with a size of Rmax =84 \pm 33 at the 90% level of confidence.Comment: 7 pages, 3 figures, accepted for publication in SCIENCE CHINA
Physics,Mechanics & Astronom
Do domestic and foreign exporters differ in learning by exporting? Evidence from China
In view of the importance of intra-firm trade and export-platform FDI conducted by multinationals, we investigate how domestic firms and foreign affiliates exhibited differential impacts of export entry and exit on productivity changes. Using a comprehensive dataset from China's manufacturing industries, we employ the Olley-Pakes method to estimate firm-level TFP and the matching techniques to isolate the impacts of export participation on firm productivity. Robust evidence is obtained that domestic firms displayed significant productivity gains (losses) upon export entry (exit), whereas foreign affiliates showed no evident TFP changes. Moreover, the productivity gains for domestic export starters were more pronounced in high- and medium-technology industries than in low-technology ones. We explain our findings from the perspective of the technology gap theory after considering processing trade and the fragmentation of production stages in the era of globalization. © 2011 Elsevier Inc.postprin
- …