April 2022 - ITP-quantumseminare

Tomorrow's QIT Seminar 2pm HIT F31.1 & zoom
by Ladina Hausmann 29 Apr '22

29 Apr '22

Hi all, Tomorrow our visitor Lev Vaidman will tell us about 'Experimental demonstrations of exotic quantum measurements'. See below for the abstract. The talk will take place at 2pm in HIT F31.1 or on Zoom: https://ethz.zoom.us/j/362994444. Best, Ladina %%%%% Abstract: I will report first demonstrations of various types of quantum measurements. Nonlocal measurement - measurement of a property of a composite quantum system with spatially separated parts. Protective measurement - measuring expectation value of an observable with a single click. Robust weak measurement - measuring weak value of an observable with a single click. Modified interaction-free measurement: measurement that tells us that the place is empty without any particle passing through it.

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Tomorrow's QIT Seminar 2pm HIT F31.1 & zoom
by Ladina Hausmann 11 Apr '22

11 Apr '22

Hi all, Tomorrow our visitor from NUS Josep Lumbreras will tell us about ''Multi-armed quantum bandits'’. See below for the abstract. The talk will take place at 2pm in HIT F31.1 or on Zoom: https://ethz.zoom.us/j/362994444. Best, Ladina %%%%% Abstract: We initiate the study of tradeoffs between exploration and exploitation in online learning of properties of quantum states. Given sequential oracle access to an unknown quantum state, in each round, we are tasked to choose an observable from a set of actions aiming to maximize its expectation value on the state (the reward). Information gained about the unknown state from previous rounds can be used to gradually improve the choice of action, thus reducing the gap between the reward and the maximal reward attainable with the given action set (the regret). We provide various information-theoretic lower bounds on the cumulative regret that an optimal learner must incur, and show that it scales at least as the square root of the number of rounds played. We also investigate the dependence of the cumulative regret on the number of available actions and the dimension of the underlying space. Moreover, we exhibit strategies that are optimal for bandits with a finite number of arms and general mixed states. If we have a promise that the state is pure and the action set is all rank-1 projectors the regret can be interpreted as the infidelity with the target state and we provide some support for the conjecture that measurement strategies with less regret exist for this case.

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Tomorrow's QIT Seminar 2pm HIT F31.1 & zoom
by Hausmann Ladina 04 Apr '22

04 Apr '22

Hi all, Tomorrow our visitor from NUS Roberto Rubboli will tell us about ''Fundamental Limits on Correlated Catalytic State Transformations'’. See below for the abstract. The talk will take place at 2pm in HIT F31.1 or on Zoom: https://ethz.zoom.us/j/362994444. Best, Ladina %%%%% Abstract: Determining whether a given state can be transformed into a target state using free operations is one of the fundamental questions in the study of resources theories. Free operations in resource theories can be enhanced by allowing for a catalyst system that assists the transformation and is returned unchanged, but potentially correlated, with the target state. While this has been an active area of recent research, very little is known about the necessary properties of such catalysts. Here, we prove fundamental limits applicable to any correlated catalytic transformation by showing that a small residual correlation between catalyst and target state implies that the catalyst needs to be highly resourceful. In fact, the resources required diverge in the limit of vanishing residual correlation. We develop our results in a general resource theory framework and discuss its implications for the resource theory of athermality, the resource theory of coherence and entanglement theory. https://arxiv.org/abs/2111.13356

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