3,090 research outputs found
Geometric quantum gates via dark paths in Rydberg atoms
Nonadiabatic holonomic quantum computation provided a promising method to
construct high-speed geometric quantum gates. It is featured with a
near-perfect resilience to external noises, yet is found to be susceptible to
systematic errors. The latter could be partially relieved by the dark-path
scheme in the closed-system scenario. Based on an effective four-level
configuration, we here construct a universal set of nonadiabatic holonomic
controlled gates via dark paths in Rydberg atoms. Distinct from the existing
dark-path scheme, our gates can be conveniently realized and manipulated by the
off-resonant driving fields on both control atom and target atom. The driving
on the control atom can enhance significantly the robustness of the quantum
gates against systematic errors while maintaining the resilience to external
noises. Our scheme can be straightforwardly generalized to the -qubit
situation. And the three-qubit gate is less susceptible to errors than the
double-qubit one
Magnon blockade in magnon-qubit systems
A hybrid system established by the direct interaction between a magnon mode
and a superconducting transmon qubit is used to realize a high-degree blockade
for magnon. It is a fundamental way toward quantum manipulation at the level of
a single magnon and preparation of single magnon sources. Through weakly
driving the magnon and probing the qubit, our magnon-blockade proposal can be
optimized when the transversal coupling strength between the magnon and qubit
is equivalent to the detuning of the qubit and the probing field or that of the
magnon and the driving field. Under this condition, the equal-time second-order
correlation function can be analytically minimized when the
probing intensity is about three times the driving intensity. Moreover, the
magnon blockade could be further enhanced by proper driving intensity and
system decay rate, whose magnitudes outrange the current systems of cavity QED
and cavity optomechanics. In particular, the correlation function achieves
, about two orders lower than that for the photon
blockade in cavity optomechanics. Also, we discuss the effects on
from thermal noise and the extra longitudinal interaction between the magnon
and qubit. Our optimized conditions for blockade are found to persist in these
nonideal situations
Urban fire dynamics and its association with urban growth: evidence from Nanjing
Many Chinese cities currently are facing increased urban fire risks particularly at places such as urban villages, high-rise buildings and large warehouses. Using a unique historical fire incident dataset (2002–2013), this paper is intended to explore the urban fire dynamics and its association with urban growth in Nanjing, China, with a geographical information system (GIS)-based spatial analytics and remote sensing (RS) techniques. A new method is proposed to define a range of fire hot spots characterizing different phases of fire incident evolution, which are compared with the urban growth in the same periods. The results suggest that the fire events have been largely concentrated in the city proper and meanwhile expanding towards the suburbs, which has a similar temporal trend to the growth of population and urban land at the city level particularly since 2008. Most intensifying and persistent fire hot spots are found in the central districts, which have limited urban expansion but high population densities. Most new hot spots are located in the suburban districts, which have seen both rapid population growth and urban expansion in recent years. However, the analysis at a finer spatial scale (500 m × 500 m) shows no evidences of an explicit connection between the locations of new fire hot spots and recently developed urban land. The findings can inform future urban and emergency planning with respect to the deployment of fire and rescue resources, ultimately improving urban fire safety
3,9-Dimethyl-2,3-dihydrophenanthro[1,2-b]furan-4,5-dione
The title compound, C18H14O3, consists of a four-ring system which contains three six-membered rings forming a phenanthrenedione system and a five-membered 1,2-dihydromethylfuran ring. A three-dimensional supramolecular framework is formed via non-classical intermolecular C—H⋯O hydrogen bonds
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