Superradiance of ultracold cesium Rydberg |65D_(5/2)> → |66P_(3/2)>

We investigate Rydberg |65D_(5/2)> → |66P_(3/2)> superradiance in dense ultracold cesium atoms,where the ground atoms are excited to |65D_(5/2)> Rydberg states via two-photon excitation in a standard magneto-optical trap.The superradiant spectrum of |65D_(5/2)> → |66P_(3/2)> is obtained using the state-selective field ionization technique.We observe its dynamic evolution process by varying the delay time of ionization field td.The results show that the evolution process of |65D_(5/2)> →|66P_(3/2)> is much shorter than its radiation lifetime at room temperature,which verifies the superradiance effect.The dependence of the superradiance process on Rydberg atoms number N_(e) and principal quantum number n is investigated.The results show that the superradiance becomes faster with increasing N_(e),while it is suppressed for stronger van der Waals(vdW) interactions.Superradiance has potential applications in quantum technologies,and the Rydberg atom is an ideal medium for superradiance.Our system is effective for studying the strong two-body interaction between Rydberg atoms.

Genetic diversity and population genetic structure of Python bivittatus in China

The Burmese python （Python bivittatus） has recently suffered large population declines in the wild in China due to illegal capture, overexploitation, deforestation and the loss of its natural habitat. Greater knowledge of the genetic diversity and structure of wild P. bivittatus populations is needed to help ensure its effective management. In this study, we investigated the genetic diversity and population genetic structure of wild P. bivittatus in China in detail. 109 P. bivittatus individuals from five distribution areas in Guangdong （GD）, Guangxi （GX）, Hainan （HN）, Fujian （FJ） and Yunnan （YN） province of China were collected, and their genetic structure and diversity were analyzed. Eight highly polymorphic microsatellite loci were utilized to reveal high levels of genetic diversity in the P. bivittatus population. Genetic diversity was highest in GX, and lowest in GD. All geographic populations demonstrated a bottleneck effect indicating recent population decline. Fst and AMOVA analyses revealed that there was moderate genetic differentiation among the five populations, and that only 10.59 % of total genetic diversity occurred among populations. Fst values between pop- ulations were positively correlated with their geographical distances. Genetic structure analyses revealed that the HN, GX and GD populations, which were geographically closest, were assigned to a genetic cluster, while the YN and FJ populations constituted a single cluster, respectively.

Radiation-Pressure Effects in Cold-Atom Absorption Spectroscopy and Electromagnetically Induced Transparency

Radiation pressure due to the interaction between a probe light and cold atoms is investigated in a standard cesium magneto-optical trap. The radiation pressure alters the absorption spectroscopy of cold atoms, leading to line shapes and linewidths after resonant interaction that are different for positive and negative probe chirps. The difference is attributed to the radiation pressure of the probe laser, due to which atoms become accelerated at the resonance. The effect of the radiation pressure is also seen in electromagnetically induced transparency (EIT) involving an excited Rydberg level. The density matrix equation accounting for the radiation pressure is used to simulate the experiments. The simulations agree well with the measurements both for absorption and EIT spectra. We find that the effect of the radiation pressure is reduced at low probe intensities, and can be neglected when the probe intensity is smaller than Isat/2 .