Special Quantum Sciences Seminar Wednesday | Mar. 13 | 4:00 pm Jefferson 250 Luiz Davidovich Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil " Quantum Metrology: Towards the Ultimate Precision Limits in the Estimation of Parameters " Refreshments will be served The estimation of parameters plays a central role in science and technology. It is based on measurements made on probe systems undergoing a parameter-dependent process. Quantum metrology deals with the ultimate precision limits in estimation procedures, taking into account the constraints imposed by quantum mechanics. The parameters of interest could be for instance a phase displacement in an optical interferometer, the time durations of a physical process, a tiny force acting on a mesoscopic object, or the frequency of an atomic transition. The estimation error decreases with the number of resources employed in the measurement (number of probes, probe energy). Quantum mechanics imposes restrictions on the precision of the estimation, since two outgoing states corresponding to two different values of the parameter are not necessarily distinguishable, and furthermore measurements must conform to quantum constraints. On the other hand, quantum features, like entanglement and squeezing, help to increase the estimation accuracy beyond the standard limit, yielding better precision for the same amount of resources. However, the precision of recent experiments, while beginning to reach the limits imposed by quantum mechanics, is spoiled by the unavoidable influence of noise. Evaluating this effect is a difficult task. While exact results and analytical solutions are known for noiseless situations, the determination of the ultimate precision limit in the presence of noise is still a challenging problem in quantum mechanics. This talk will review some of the achievements and difficulties of quantum metrology, and will present a recently proposed method that allows the determination of precision limits for noisy systems. This method has been applied to obtain very good bounds for the precision in optical interferometry and atomic spectroscopy, as well as for the quantum speed of physical processes. Joan Hamilton Faculty Assistant to Profs. Greiner and Lukin HQOC Laboratory Administrator HUCTW Local Union Representative Harvard University Department of Physics 17 Oxford Street Cambridge, MA 02138 P: (617) 496-2544 F: (617) 496-2545