The 2018 Physics Nobel Prize was awarded “for groundbreaking inventions in the field of laser physics”. Among these inventions are the optical tweezers, which will play an important role in our next QM Talks@CBPF. This week we are pleased to welcome Diney Ether (UFRJ), who is employing optical tweezers to measure very feeble forces due to the Casimir effect. See details below, and be sure to be there!
Title: Perspectives: Probing the Casimir Effect using Optical Tweezers
Speaker: Diney Ether (UFRJ)
Coordinates: room t.b.a, CBPF. 10/10, 16h00
We propose to use optical tweezers to probe the Casimir interaction between microspheres inside a liquid medium. This setup has the potential for revealing unprecedented features associated either with the Casimir force screening by movable ions in solution and the non-trivial role of the spherical curvatures achieved by going beyond the validity of the widely employed proximity force approximation. We will show some current experimental results with polystyrene microspheres immersed in water at distances below 500nm by employing very soft optical tweezers, with stiffness in the scale of fN/nm. Finally, we also described some theoretical results and future perspectives to suppress the electrostatic double-layer force always present in this context, and some theoretical results concerning light reverberation between the microspheres. This line of investigation has the potential for bringing together different fields including classical and quantum optics, statistical physics and colloidal science, while paving the way for novel quantitative applications of optical tweezers in cell and molecular biology.
D. S. Ether, L. B. Pires et al, EPL 112, 44001 (2015).
D. S. Ether, F. S. S. Rosa et al, PRE 97, 022611 (2018).
Estão abertas as inscrições para 4a Escola Avançada de Física Experimental (EAFExp) do CBPF!
Nesta escola estudantes de graduação e de pós-graduação têm a oportunidade de entrar em contato com os pesquisadores do CBPF e suas linhas de pesquisa, além de entrarem em contato com diversas técnicas experimentais em diferentes áreas da Física.
Na EAFExp os alunos são separados em pequenos grupos e cada grupo é inserido em apenas um módulo (curso) da escola. Assim, os estudantes têm a oportunidade de conhecer a fundo como são as atividades de pesquisa de um físico experimental. Esta característica faz desta uma escola especial onde os estudantes selecionados passam duas semanas realizando atividades de pesquisa que incluem o planejamento dos estudos experimentais a serem realizados, realização dos experimentos em equipamentos de última geração, análise de dados e apresentação de seminários relatando seus resultados para professores e outros estudantes da própria escola.
A 4a EAFExp ocorrerá entre 4 e 15 de fevereiro de 2019. As inscrições se encerram no dia 15 de novembro de 2018.
Home page: www.cbpf.br/eafexp/
Title: Time, coherence and quantum reference frames
Speaker: Diogo O. Soares-Pinto (USP-SC)
Coordinates: COEDU meeting room, 6th floor, CBPF. 26.09, 14h00
Abstract: The Page and Wootters’ mechanism questioned the fundamental nature of time in quantum physics. The mechanism explored the notion that a given physical quantity is always defined and measured relative to a reference frame, in general, not explained in the theoretical description of quantum physical experiments. Recently, the new area of quantum information theory named resource theory of asymmetry deals explicitly with what are the physical conditions for a quantum system to serve as a good reference frame. In this work, we use this machinery in the Page and Wootters’ mechanism by identifying the concept of local time-asymmetry as relative coherence and establishing an operational theory of relative coherence in a composed quantum systems. To do so, the notion of quantum coherence in relation of a quantum reference frame is revisited and a quantifier is proposed in this scenario. Also, this open space to investigate the link of relative coherence and correlations, as proposed by Page and Wootters, under a resource theory approach.
Title: Quantum revival patterns from classical phase-space trajectories
Authors: Gabriel M. Lando, Raúl O. Vallejos, Gert-Ludwig Ingold, Alfredo M. Ozorio de Almeida
Abstract: A general semiclassical method in phase space based on the final-value representation of the Wigner function is discussed that bypasses caustics and the need to search for classical trajectories. We demonstrate its potential by applying the method to the Kerr Hamiltonian. Fractional revivals sensitive to details in the quantum evolution are obtained semiclassically and provide decisive evidence for the validity of the approach far beyond the Ehrenfest time. There is no constraint on the initial state as is shown by reproducing fractional revivals not only for the usual coherent states but also for a shifted weakly excited Fock state.