Studiul Energiei de Simetrie in Zona de Densitate Supranormala
Dan Cozma, DFT
08.06.2017
Obiectivul proiectului consta in extragerea de constrangeri pentru dependenta de densitate a partii dependente de izospin a ecuatiei de stare a materiei nucleare (energia de simetrie) in zona de densitate 2ρ0 (ρ0 - densitatea de saturatie) . Cunoasterea proprietatilor acesteia sunt necesare pentru intelegerea proprietatilor stelelor neutronice sau exploziilor de supernove. Se va folosi un model de transport de tip QMD cuplat cu un model de coalescenta pentru determinarea spectrelor finale de fragmente formate in ciocnirile de ioni grei (in principal Au+Au) la energii de impact in jurul valorii de 400 MeV/nucleon. Spectrele de multiplicitati si curgerile radiale si eliptice ale nucleonilor si fragmentelor usoare dependente de impulsul transversal vor fi de interes special. Primele vor fi utile, prin compararea cu datele experimentale ale colaborarilor FOPI si FOPI-LAND, la imbunatarea modelului folosit. Compararea cu datele experimentale obtinute de colaborarile FOPI-LAND si ASYEOS ale raportului de curgere eliptica neutron/proton si neutron/fragmente usoare va permite extragere de constrangeri pentru dependenta de densitatea a energiei de simetrie, exprimate prin determinarea valorilor permise pentru panta L si curbura Ksym a acesteia la saturatie. Se vor prezenta rezultatele unui studiu privind energia de impact optima si/sau observabila optima pentru masuratori experimentale viitoare (ASYEOS 2 si NUSTAR/FAIR).
Proiect Nucleu PN 16 42 01 01 (2017)
A Sheaf Theoretic Approach to Quantum Contextuality
Carmen Constantin, Oxford University
29 Mai 2017, ora 10:45
Abstract
At a fundamental level, the key features that set apart quantum phenomena from classical behaviour are contextuality, non-locality and entanglement. These also constitute the prime resources for quantum information technology. In describing such phenomena the standard Hilbert space formalism is often clumsy; for instance, it is difficult to define unambiguously a measure of entanglement for multi-partite entangled states, entropy being only a coarse indicator for which quantum state is more entangled than another. As such, it has been felt that a more general approach is needed in order to capture the non-classical features of quantum mechanics. The sheaf theoretic approach formulated by Abramsky and Brandenburger provides a novel framework for discussing non-locality and contextuality. In particular, this setting naturally leads to a three level hierarchy of quantum contextuality: weak, logical and strong contextuality, and we enumerate a series of classification results which we obtained in recent years. The most surprising aspect of this classification is that almost all n-qubit quantum states are logically non-local, and moreover n+2 observables are sufficient to witness this non-locality. This relates to an earlier result of Popescu and Rohrlich which has recently received renewed attention.
Postquantum Steering
Dr. Ana Belen Sainz, Perimeter Institute for Theoretical Physics.
29 mai 2017, ora 9:30
Abstract:
The discovery of postquantum nonlocality, i.e. the existence of nonlocal correlations stronger than any quantum correlations but nevertheless consistent with the no-signaling principle, has deepened our understanding of the foundations quantum theory. In this work, we investigate whether the phenomenon of Einstein-Podolsky-Rosen steering, a different form of quantum nonlocality, can also be generalized beyond quantum theory. While postquantum steering does not exist in the bipartite case, we prove its existence in the case of three observers. Importantly, we show that postquantum steering is a genuinely new phenomenon, fundamentally different from postquantum nonlocality. Our results provide new insight into the nonlocal correlations of multipartite quantum systems.
Efect par-impar si masa efectiva in fisiunea nucleara din ecuatiile de miscare microscopice
M. Mirea, DFT
25.05.2017
Rezumat:
Ecuatiile de imperechere dependente de timp sunt obtinute din principiul variational. Acestea ne dau probabilitatile de ocupare BCS ale nivelelor uniparticula atunci cand un sistem nuclear se deformeaza in timp. Aceste ecuatii au fost generalizate pentru a introduce mecanismul de promovare Landau-Zener. In acest mod s-a evidentiat un nou efect dinamic de spargere de perechi Cooper in timpul dezintegrarilor nucleare. De asemenea, prin luarea in considerare a elementelor de matrice ale operatorilor derivatei fata de timp, s-a putut deduce o formula pentru masa efectiva care depinde de energia disipata. Pentru sisteme adiabatice, particularizarea acestui formalism conduce la binecunoscuta formula pentru inertia cranking.
Collective dynamics in coupled quantum emitter systems
Claudiu Genes, Max Planck Institute for the Science of Light, Erlangen
24.11.2017
Abstract:
Dynamics in ensembles of quantum emitters (atoms, molecules, ions, Rydberg atoms, quantum dots etc) at low versus high densities can be fundamentally different. As particles get closer together, strong environment-mediated interactions start playing an important role both in the coherent (such as dipole-dipole interactions) as well as in the incoherent evolution (super- /subradiance). Furthermore, replacing the naturally occurring environment with an engineered one (such as an optical cavity) stronger interactions can be designed and utilized. In the first part of my talk I will briefly review recent activities aimed at: i) exploiting this inherent collective dynamics to perform more precise frequency measurements in the context of Ramsey interferometry [1], ii) selectively and efficiently prepare robust multipartite entangled states [2], and iii) enhancing exciton and charge transport in the context of cavity strong coupling regime [3–5]. In the second part of the talk I will detail a newly proposed platform for the realization of strong cooperativity inside optical cavities with weakly coupled quantum emitter ensembles [6].
References
[1] L. Ostermann, H. Ritsch, and C. Genes, “Protected state enhanced quantum metrology with interacting two-level ensembles,” Phys. Rev. Lett. 111, 123601 (2013).
[2] D. Plankensteiner, L. Ostermann, H. Ritsch, and C. Genes, “Selective protected state preparation of coupled dissipative quantum emitters,” Scientific Reports 5, 16231 (2015).
[3] J. Schachenmayer, C. Genes, E. Tignone, and G. Pupillo, “Cavity-enhanced transport of excitons,” Phys. Rev. Lett. 114, 196403 (2015).
[4] E. Orgiu, J. George, J. Hutchison, E. Devaux, J. F. Dayen, B. Doudin, F. F. Stellacci, C. Genet, J. Schachenmayer, C. Genes, G. Pupillo, P. Samori, and T. W. Ebbesen, “Conductivity in organic semiconductors hybridized with the vacuum field,” Nature Materials 14, 1123 – 1129 (2015).
[5] D. Hagenmüller, J. Schachenmayer, S. Schütz, C.Genes, and G. Pupillo, “Cavity-enhanced transport of charge,&r2dquo; arXiv:1703.00803 (2017).
[6] D. Plankensteiner, C. Sommer, H. Ritsch, and C. Genes, “Cavity antiresonance spectroscopy of dipole coupled subradiant arrays,” arXiv:1703.06039 (2017).
Yukawa Couplings in Heterotic String Theory
Andrei Constantin
Department of Physics and Astronomy, Uppsala University, Sweden
28.02.2017
Abstract:
I will present some recent progress towards the challenging task of computing Yukawa couplings within a class of phenomenologically viable string models. Computing physical Yukawa couplings depends on the knowledge of the matter field Kahler metric which, in turn, amounts to knowing the Calabi-Yau metric and the hermitian Yang-Mills connection on the holomorphic vector bundle. These, however, can only be computed numerically and for fixed values of the moduli, using a tremendously complex algorithm. Instead of that, I will describe an analytic method that retains the moduli dependence of the Yukawa couplings. The method relies on the observation that, in the regime of large fluxes, the integrals that define the Yukawa couplings localise on the compactification manifold to the extent that the precise knowledge of the Calabi-Yau metric becomes irrelevant.
