Hi all,
Tomorrow we will have two talks. Carla Ferradini will tell us about her semester project with Vilasini, entitled 'A causal modelling framework for classical and quantum cyclic causal structures' and Arman Pour Tak Dost will tell us about his master thesis with Mischa Woods entitled 'Quantum advantages in low-dimensional timekeeping'. See below for the abstracts. The talks will take place at 2pm in F31.1 or on Zoom: https://ethz.zoom.us/j/362994444.
Best, Ladina
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Title: A causal modelling framework for classical and quantum cyclic causal structures
Abstract: In 1937 the theoretical existence of closed time-like curves (CTCs) as solutions in General Relativity was discovered. These are time-like curves that allow a particle to return to its starting point in space-time and, thus, seem to imply that time travel backwards in time is theoretically possible. This gives rise to several paradoxes such as the well-known grandfather paradox. Therefore, it is of physical interest to characterise and give a description of such closed time-like curves from a causal point of view and derive logically consistent solutions. The study of these solutions requires to introduce cyclic causal models and deduce how to evaluate probability distributions. Here, we provide a method that allows us to determine whether an arbitrary cyclic causal graph admits a logically consistent solution and eventually evaluate probabilities. This method can be used both in classical or quantum scenarios. In both cases, we prescribe how to reduce the initial causal graph to an acyclic one and then recover cyclicity through post-selection. Classically, we show that for an acyclic graph this reduces to the joint probability distribution that can be derived using the classical theory of acyclic causality. In the quantum scenario, we also show the equivalence between loop composition of the causal box framework and post-selected CTCs in our formalism. The obtained results do not only describe CTCs that may arise in exotic solutions of General Relativity, but also can be used to model ordinary feedback processes.
Title: Quantum advantages in low-dimensional timekeeping
Abstract: This presentation will discuss quantum advantages in timekeeping. We derive analytical formulas for the regularity of quantum clocks, numerically optimized to prove the quantum advantage in low dimensions. We provide heuristics based on a dynamical approach that reveals the clock as a damped harmonic oscillator. Further, we propose an experimental setup that uses weak coupling, spontaneous emission, and large decay rates to obtain a Lindblad equation beyond the rotating wave approximation, which can be viewed as a fingerprint of the energy-time uncertainty relation. Lastly, we provide a connection between clocks and the fundamental linewidth of lasers.