Seminář se koná každé úterý v 10:40 v posluchárně ÚTF MFF UK
v 10. patře katedrové budovy v Tróji, V Holešovičkách 2, Praha 8
When a gas of identical atoms about a million times thinner than air is cooled down to about a millionth of a degree above absolute zero, quantum mechanical effects become important and the gas can enter various exotic phases of matter such as the Bose-Einstein condensate (BEC). In the last three decades, such cold atomic gases have been used with great success as a highly controllable platform for studying diverse many-body phenomena. I will give a brief introduction to the field and to our experiments with ultracold atoms in optical box traps, and later discuss some of our recent studies focusing in particular on 1) far-from-equilibrium dynamics of Bose gases and 2) physics of impurities immersed in a Bose-Einstein condensate.
Due to the exponential progress in laser technology, ultra-intense lasers are quickly becoming an essential tool to probe quantum electrodynamics phenomena. These include e.g. radiation of accelerated charged particles, particle-antiparticle pair production, and polarization of vacuum. After a brief overview of these effects, we will discuss “Flying Focus” (FF) laser pulses which enable co-propagation of particle beams (e.g. ultra-relativistic electrons or hard photons) with the laser focus, so that they stay in the region of peak field intensity for prolonged interaction times. We will introduce FF generation methods and analytical description of FF pulses with arbitrary focal velocities and discuss experimental configurations in which the long laser-particle interaction time aids high-intensity applications. Since signatures of strong field effects in laser-particle interactions accumulate with interaction time, the FF regime enables experimental access at orders of magnitude lower laser powers and intensities than in conventional fixed-focus setups. Even more importantly, in the quantum regime of the laser-electron interaction the energy loss and photon yield scale more favorably with the interaction time than the laser intensity, giving FF an outright advantage over fixed-focus pulses.
Our Sun is a single star, which is somewhat of an exception in the Universe as most stars are found in binary and multiple systems. For a wide range of initial conditions at stellar birth, the two stars in a binary will interact by exchanging mass, exploding, or merging to a single object. Computer simulations of binary systems are indispensable in revealing the fundamental physical processes governing the binary's structure and evolution, yet they are complicated by a lack of any useful symmetry. In this talk I will review results of radiation / magneto-hydrodynamical simulations of a certain evolutionary phase studied with the help of ERC StG and describe plans for a new set of simulations with discontinuous Galerkin method to be done with the support of ERC CoG.
Jiří Horáček David Heyrovský