Title: Quantum Mechanics Without Wavefunctions
Speaker: Bill Poirier (Texas Tech University)
Coordinates: sala 601C, CBPF. 21/01, 14h30
Abstract: In David Bohm’s causal/trajectory interpretation of quantum mechanics, a physical system is regarded as consisting of BOTH a particle and a wavefunction, where the latter “pilots” the trajectory evolution of the former. In this presentation, we show that it is possible to discard the pilot wave concept altogether, thus developing a complete mathematical formulation of time-dependent quantum mechanics directly in terms of real-valued trajectories alone. Moreover, by introducing a kinematic definition of the quantum potential, a generalized action extremization principle can be derived. The latter places very severe a priori restrictions on the set of allowable theoretical structures for a dynamical theory, which is shown to include both classical mechanics and quantum mechanics, and a few other possibilities. Beneficial numerical ramifications of the above, “trajectories only” approach are also discussed.
Title: On the geometrical hypotheses underlying wave functions and their emerging dynamics
Speaker: Nelson Pinto (CBPF)
Coordinates: auditório do 6o andar, CBPF 05/12, 16h30.
Abstract: Classical mechanics for individual physical systems and quantum mechanics of non-relativistic particles are shown to be exceptional cases of a generalized dynamics described in terms of maps between two manifolds, the source being configuration space. The target space is argued to be 2-dimensional and flat, and their orthogonal directions are physically interpreted. All terms in the map equation have a geometrical meaning in the target space, and the pull-back of its rotational Killing one-form allows the construction of a velocity field in configuration space. Identification of this velocity field with tangent vectors in the source space leads to the dynamical law of motion. For a specific choice of an arbitrary scalar function present in the map equation, and using Cartesian coordinates in the target space, the map equation becomes linear and can be reduced to the Schrödinger equation. We link the bi-dimensionality of the target space with the essential non-locality of quantum mechanics. Many extensions of the framework here presented are immediate, with deep consequences yet to be explored.
Candidata: Isadora Barbosa Lima Veeren,
Título da dissertação: Entropic uncertainty relations and classicality
Coordenadas: 30 de Abril às 16h. CBPF, auditório do sexto andar.
Banca: Fernando de Melo (CBPF), Bárbara Amaral (UFSJ*), Daniel Schneider Tasca (UFF), Ivan de Oliveira (CBPF) e Roberto Sarthour (CBPF).
Estão todxs convidadxs!
*não poderá participar.
Título: Como confiar nas tecnologias quânticas de muitos corpos?
Palestrante: Mario Leandro Aolita (UFRJ)
Coordenadas: sala 601C, CBPF. 04/04, 16h00
Resumo: Recentemente houve um progresso experimental impressionante em tecnologias quânticas de muitos corpos. No entanto, ainda não temos ferramentas práticas de certificação que nos permitam garantir se os dispositivos quânticos experimentais que construímos funcionam adequadamente. De fato, uma vez que a simulação clássica de sistemas quânticos é uma tarefa computacionalmente difícil — exponencial no número de partículas — o paradigma usual de “predizer e comparar com o experimento” torna-se inaplicável. Este é um dos maiores obstáculos para as tecnologias quânticas de grande escala. Neste seminário, falarei sobre avanços recentes na validação de computadores quânticos e simuladores quânticos de muitos corpos. Em particular, discutirei testemunhas de fidelidade para simulações quânticas de bosons e para cadeias de spins, computação quântica verificável e tomografia de estado quântico assistida por redes neurais nativas de aprendizado de máquina sem supervisão.
Title: Spin-entanglement wave in a coarse-grained optical lattice
Authors: Pedro Silva Correia, Fernando de Melo
Abstract: In the present work we explore a suitable coarse graining channel as a tool to describe entanglement spreading in a coarse-grained spin-chain with different degrees of resolution. Comparing with the experimental realizations performed with ultracold atoms, our results suggest that even if we are not able to fully resolve the system, entanglement can still be detected for some coarse graining levels. Furthermore, we show that it is possible to have some information about the “microscopic” entanglement, even if we have access only to the system’s coarse graining description. We show that the amount of entanglement decays exponentially with the lack of system resolution. The lack of experimental resolution might thus lead to a classical effective description.
The year is about to finish… but we continue full power. This week our series of seminars QM Talks@CBPF, have the pleasure to welcome Alexis Hernández, from the Federal University of Rio de Janeiro. Alexis has many interests within physics (and outside of it as well!). This time he’ll tell us about a nonlinear description of Hall voltages. See details below.
Title: Investigating transverse Hall voltages using two-terminal setups
Speaker: Alexis Hernández (UFRJ)
Coordinates: room 601C, CBPF. 06/12, 16h00
Abstract: In this talk, we present a method to numerically study transverse Hall voltages using an alternative quantity in two-terminal setups. Using nonlinear transport concepts, we find that the Hall voltage dependence on the model parameters can be investigated from the difference between the injectivities of each terminal. The method is suitable to work with nonequilibrium Green’s functions as well as for scattering matrix approaches. We illustrate the proposed idea by studying the quantum spin Hall effect in graphene with disordered spin-orbit scattering centers induced by adatoms. We use two distinct models: a finite-difference implementation of the Dirac Hamiltonian and a tight-binding Hamiltonian combined with the scattering matrix approach and the nonequilibrium Green’s functions approach, respectively.