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 $N$-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 $g^{(2)}(0)$ 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 $g^{(2)}(0)\sim10^{-7}$, about two orders lower than that for the photon blockade in cavity optomechanics. Also, we discuss the effects on $g^{(2)}(0)$ 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