اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSolitons as the early stage of quasicondensate formation during evaporative cooling
157
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We calculate the evaporative cooling dynamics of trapped one-dimensional Bose-Einstein condensates for parameters leading to a range of condensates and quasicondensates in the final equilibrium state. We confirm that solitons are created during the evaporation process, but always eventually dissipate during thermalisation. The distance between solitons at the end of the evaporation ramp matches the coherence length in the final thermal state. Calculations were made using the classical fields method. They bridge the gap between the phase defect picture of the Kibble-Zurek mechanism and the long-wavelength phase fluctuations in the thermal state.
قيم البحث
اقرأ أيضاً
We report the realization of Bose-Einstein condensates of 39K atoms without the aid of an additional atomic coolant. Our route to Bose-Einstein condensation comprises Sub Doppler laser cooling of large atomic clouds with more than 10^10 atoms and eva
porative cooling in optical dipole traps where the collisional cross section can be increased using magnetic Feshbach resonances. Large condensates with almost 10^6 atoms can be produced in less than 15 seconds. Our achievements eliminate the need for sympathetic cooling with Rb atoms which was the usual route implemented till date due to the unfavourable collisional property of 39K. Our findings simplify the experimental set-up for producing Bose-Einstein condensates of 39K atoms with tunable interactions, which have a wide variety of promising applications including atom-interferometry to studies on the interplay of disorder and interactions in quantum gases.
The fluctuations in thermodynamic and transport properties in many-body systems gain importance as the number of constituent particles is reduced. Ultracold atomic gases provide a clean setting for the study of mesoscopic systems; however, the detect
ion of temporal fluctuations is hindered by the typically destructive detection, precluding repeated precise measurements on the same sample. Here, we overcome this hindrance by utilizing the enhanced light--matter coupling in an optical cavity to perform a minimally invasive continuous measurement and track the time evolution of the atom number in a quasi two-dimensional atomic gas during evaporation from a tilted trapping potential. We demonstrate sufficient measurement precision to detect atom number fluctuations well below the level set by Poissonian statistics. Furthermore, we characterize the non-linearity of the evaporation process and the inherent fluctuations of the transport of atoms out of the trapping volume through two-time correlations of the atom number. Our results establish coupled atom--cavity systems as a novel testbed for observing thermodynamics and transport phenomena in mesosopic cold atomic gases and, generally, pave the way for measuring multi-time correlation functions of ultracold quantum gases.
We demonstrate experimentally the evaporative cooling of a few hundred rubidium 87 atoms in a single-beam microscopic dipole trap. Starting from 800 atoms at a temperature of 125microKelvins, we produce an unpolarized sample of 40 atoms at 110nK, wit
hin 3s. The phase-space density at the end of the evaporation reaches unity, close to quantum degeneracy. The gain in phase-space density after evaporation is 10^3. We find that the scaling laws used for much larger numbers of atoms are still valid despite the small number of atoms involved in the evaporative cooling process. We also compare our results to a simple kinetic model describing the evaporation process and find good agreement with the data.
We study the formation of an exciton condensate in GaAs coupled quantum wells at low temperatures. We show that the condensate consists of dark excitons, and extends over hundreds of {mu}m, limited only by the boundaries of the mesa. We find that the
condensate density is determined by spin flipping collisions among the condensate excitons and with the thermal bath. We show that these processes, which convert dark excitons to bright, evaporatively cool the system to temperatures that are much lower than the bath temperature. We present a rate equations model, which explains the temperature and power dependence of the exciton density, and in particular - the large density buildup at low temperatures. We confirm the validity of the model by reproducing the unique behavior observed when a magnetic field is applied in a direction parallel to the layers.
We discuss on the early stage of galaxy formation based on recent deep surveys for very high-redshift galaxies, mostly beyond redshift of 6. These galaxies are observed to be strong Lyman$alpha$ emitters, indicating bursts of massive star formation i
n them. The fraction of such star-forming system appears to increase with increasing redshift. On the other hand, the star formation rate density derived from Lyman$alpha$ emitters tends to decrease with increasing redshift. It is thus suggested that the major epoch of initial starbursts may occur around $z sim$ 6 -- 7. In order to understand the early stage of galaxy formation, new surveys for galaxies beyond redshift of 7 will be important in near future.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
