This Thursday (April 27th), we will have a Purdue Quantum Center theory seminar in Birck Nanotechnology Center at 11:00 am in Room 2001. The speaker is Prof. Francesco Ciccarello. Title: What is Markovian and non-Markovian in Quantum Mechanics: new approaches and viewpoints Title: What is Markovian and non-Markovian in Quantum Mechanics: new approaches and viewpoints Abstract While in classical physics the notion of what is Markovian or not is well defined, this is not the case when it comes to open quantum systems. What makes a quantum dynamics Markovian or non-Markovian (NM)? Traditional answers to this question involve the celebrated Lindblad master equation (ME) and/or the ability of an open dynamics to be governed by a time-local ME. The last few years, yet, witnessed a thorough revision of such concepts with the aim to establish in a rigorous way exact criteria for assessing whether or not a dynamics is NM and even quantifying its degree of quantum “non-Markovianity”. This resulted in a number of “non-Markovianity measures” that have been put forward. Based on these and a number of theoretical advancements, the lack of a Lindblad ME or time-local ME turns out not to be a reliable criterion. For instance, there are Markovian dynamics that are not described by a Lindblad ME, while, on the other hand, many open dynamics that are strongly NM can be shown to effectively obey a time-local ME. After reviewing these new concepts, in the last part of the talk I discuss a problem where they are used to tackle the question as to whether or not the dynamics of a qubit undergoing single-photon scattering in a waveguide is Markovian. It turns out that, in the infinite-waveguide case, the dynamics is NM when the photon-wavepacket width is comparable with the qubit-field coupling rate. In the semi-infinite waveguide case (mirror-like boundary condition), this source of non-Markovianity adds to that due to the photon delay time (owing to the finite qubit-mirror distance). Bio Francesco Ciccarello is an Italian Assistant Professor (“Ricercatore”) at University of Palermo, Italy and member of NEST, Scuola Normale Superiore, Pisa, Italy. He is currently a Fulbright Research Scholar at Duke University, Duhram, NC, in the Harold Baranger group. He works within the broad area of quantum information, his present research interests being focused on open quantum systems theory, waveguide QED and cavity QED. In recent years, he in particular made contributions to quantum collision models, quantum correlations beyond entanglement and scattering-based implementations of quantum information processing tasks.