The derivation of exact results for quantum Coulomb gases has to face several difficulties originating from screening and recombination of charges into atoms, ions and molecules. The path integral representation at finite temperature is the most suitable tool for a proper account of those phenomena in partially ionized gases. It leads to the introductionof an equivalent classical system made of loops with arbitrary shapesdistributed according to Wiener measure. The equilibrium quantities of thegenuine quantum gas are then formally represented by Mayer-likediagrammatical series for that system of loops. The path integraldescription in terms of loops allows us to perform systematic resummations of Coulomb chains which remove long range divergences, as well as reexponentiations which incorporate recombination at short distances. Such operations can be carried out within well-prescribed topological and combinatorial rules, thanks to the classical nature of Gibbs factors in the loop world. Mayer-like series are then exactly transformed into the so-called screened cluster representation, where graphs are now built with particle clusters and screened interactions.
Within the screened cluster representation, we derive exact expressions for both thermodynamics and correlations of a partially ionized hydrogen gas in the Saha regime, defined by a double zero-temperature and zero-density limit. Such expressions properly account for contributions of molecular or ionic species, without any adjustable parameters like in phenomenological approaches. Moreover, they shed light on the partial screening of van der Waals forces by free charges, and its relation with the algebraic nature of screening in quantum plasmas.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
dr hab. Piotr Flin, prof. UJK (Wydział Matematyczno-Przyrodniczy Uniwersytetu Jana Kochanowskiego, Kielce)
Przedstawione będzie życie Silbersteina od czasów szkolnych do ukończenia studiów, jak też niektóre elementy życia prywatnego. Krótko omówię główne kierunki działalności naukowej i dydaktycznej. Pokuszę się o próbę oceny jego osiągnięć i wpływu na rozwój fizyki.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
Prof. dr hab. Krzysztof M. Gorski (Jet Propulsion Laboratory of the California Institute of Technology, Pasadena, CA and Warsaw University Observatory)
Since August 2009 Planck has been observing the sky at frequencies from 30 to 857 GHz, measuring its principal target - the cosmic microwave background, but also everything else in the universe that radiates at these frequencies. I will describe the design and scientific goals of the mission, and the first scientific results from Planck, presented in Jan. 2011, covering a wide range of galactic and extragalactic astrophysics.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
prof. dr hab. Tomasz Dietl (Laboratory of Cryogenic and Spintronic Research, Institute of Physics, Polish Academy of Sciences; Institute of Theoretical Physics Faculty of Physics University of Warsaw)
To memory of Jan Gaj (1943-2011)
In course of the years, the origin of spontaneous magnetisation that has been observed in numerous semiconductors and oxides has arguably become one of the most controversial topics in the contemporary physics of condensed matter. After a general introduction to spintronics and magnetically doped semiconductors, I will argue [1] that surprising properties of these systems have two distinct roots (i) an intricate interplay between hole-mediated ferromagnetism and AndersonMott localisation and (ii) a highly non-random distribution of magnetic cations driven by a significant contribution of open d shells to the cohesive energy.
[1] see, T. Dietl, Nature Mat. 9, 965 (2010), and references therein.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
Prof. Dr. W. Hofstetter (Goethe-Universität Frankfurt)
Cold atoms in optical lattices offer a new laboratory for quantum many-body phenomena. One of their main advantages is the high tunabilityof interactions and quantum statistics. In this colloquium I will focus on current developments in multiflavor Fermi gases:
i) We investigate antiferromagnetic ordering of trapped spin-1/2 fermions using large-scale dynamical mean-field theory simulations. We find a clear experimental signature - enhanced double occupancy - for the onset of magnetic order at low temperatures in current experiments.
ii) We study the properties of three-flavor fermions in an optical lattice, where new exotic quantum states such as color superfluids arise in partial analogy to Quantum Chromodynamics. Low-temperature properties of this system are addressed using DMRG and dynamical mean-field theory. Wefind a strong interplay between magnetization and color superfluidity.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
Dr. Randolf Pohl (Ludwig-Maximilians-Universität, Munich;Max-Planck-Institute of Quantum Optics, Garching)
The charge radius Rp of the proton has so far been known only with a surprisingly low precision of about 1% from both electron scattering and precision spectroscopy of hydrogen.
We have recently determined Rp by means of laser spectroscopy of the exotic "muonic hydrogen" atom. Here, the muon, which is the 200 times heavier cousin of the electron, orbits the proton with a 200 times smaller Bohr radius. This enhances the sensitivity to the proton's finite size tremendously.
Our new value Rp = 0.84184 (67) fm is ten times more precise than the generally accepted CODATA value, but it differs by 5 standard deviations from it. A lively discussion about possible solutions to the "proton size puzzle" has started.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
Prof. Dr. Dagmar Bruss (Institut fuer Theoretische Physik III Heinrich-Heine-Universitaet Duesseldorf)
Entanglement is one of the most fascinating features of quantum mechanics, and enables various protocols in quantum information processing. The aim of this talk is to give an overview of methods for the theoretical analysis of entanglement, and to provide a link to the detection of entanglement in the laboratory. Special emphasis will be given to the method of witness operators. In the context of measuring witness operators, a connection between entanglement and diffractive properties of periodic spin systems will be pointed out.
Zapraszamy do Sali Dużej Doświadczalnej, ul. Hoża 69 o godzinie 16:30
Prof. Kenneth G. Wilson Additional future funding for physics research might come from two different sources. One source, not yet visible, could be research grants from the private sector provided for a subgroup of physicists. These physicists would have already been recruited to participate in a future decades-long career development ladder for increasingly highly paid future top organizational executives. These physicists would (presumably) have already agreed to complete a first career in physics and then launch a second career as an aspiring top executive leader nationally or internationally. They might be selected for recruitment to such second careers based on their already demonstrated leadership skills in sizeable physics research projects (engaging perhaps ten or more physicists). They could then be helped to interpret and learn from their continuing experience as a leader in such projects for a number of years prior to making their switch to their second career. The amount of funding provided through such research grants as part of their incentive to agree to make aswitch to a second career could be quite substantial. The amount of such funding could grow with time as the need for exceedingly capable executive leaders, already acute and largely unmet as of 2010, continues to grow. I know from private conversations that a first career in physics can provide an invaluable background in creative thinking, problem solving, and pushing for unceasing innovation by a person who later joins a career ladder headed for top executive leadership positions. Another source, already non-trivial in magnitude but likely to increase in the future, will be discussed far more briefly. It is the need to ensure ever-increasing reliability, through increasingly careful testing, of the underlying physical laws governing physics-based instrumentation used in multi-billion-dollar and increasingly costly applications in medicine, aviation, chemical engineering, astronomy and space research, and the like.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
prof. Krzysztof Meissner (IFT UW, IPJ)
I will discuss theoretical motivations for the existence of axions and bounds on their masses and interactions coming from astrophysics andcosmology. I will describe arguments to propose axions as natural ColdDark Matter candidates. I will present existing experiments searching foraxions and in particular experiment OSQAR at CERN. On the theory sideslightly enlarged Standard Model with conformal symmetry naturallyincludes axions as (pseudo)Goldstone bosons of spontaneously broken lepton number symmetry with very small couplings correlated with small neutrino masses.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
Prof. Jacek A. Majewski (IFT UW)
Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, has attracted a lot of attention since its discovery in 2004. The material with the whole plethora of intriguing properties has been billed as wonder material that could one day determine the future nano-electronics, just replacing the silicon in processors. Actually, a 100 GHz field effect transistor based on graphene sheet has been announced recently.
In this lecture, we present a survey of the graphene properties that lead to intriguing physics (resembling relativistic physics) and make this material so promising candidate for future information technologies. We address the challenges of creating electronic devices built of graphene. We consider electronic structure of monolayer graphene flakes, multilayers of graphene obtained in epitaxial growth process, and recently obtained graphane (i.e., modification of graphene sheet covered with hydrogen atoms), which also is intensively studied.
Zapraszamy do Nowej Auli (425), ul. Hoża 69 o godzinie 15:30
Dr Carsten Müller (Max-Planck-Institut für Kernphysik, Heidelberg, Germany)
The creation of particle-antiparticle pairs by multiphoton absorption from intense laser fields in various configurations is discussed.Electron-positron pair creation by high-energy proton impact on a strong laser beam is considered first, including spin and recoil effects. Acomparison is drawn with pair creation in relativistic electron-laser collisions. The creation of muon-antimuon pairs is also addressed.Finally, we consider electron-positron pair creation in a standing electromagnetic wave formed by two counter-propagating laser beams.
Zapraszamy do Sali Dużej Doświadczalnej, ul. Hoża 69 o godzinie 16:30
prof. dr hab. Bogdan Mielnik (IFT UW oraz Departamento de Fisica, Cinvestav, Mexico)
Współczesne teorie kwantowe zrodziły się w toku trudnych polemik i nawracających wątpliwości. Czy warto zachować je w pamięci? Mój mini-wykład będzie przeglądem niektórych pytań, na które odpowiedź znamy, innych, które pozostały otwarte, innych jeszcze, których wolimy nie zadawać.
Dlaczego wierzymy w istnienie kwantów energii? Czy ich teoria musi być indeterministyczna?Czy funkcja falowa opisuje pojedyncza cząstkę? Czy redukcja pakietu falowego jest prawdą, czy fikcją?Czy ma miejsce zjawisko teleportacji w doświadczeniach typu Einstein-Podolsky-Rosen?Czy pojedynczy foton może wykryć bombę w odległości tysiąca km?Czy nasze drzewo wiadomości dobrego i złego jest obiektywne?