Tomorrow Mischa will tell us about one of his recent projects, entitled "How to tell the time with a clock that's always off." See below for the abstract. We'll start at 2pm in zoom: https://ethz.zoom.us/j/362994444. 

Best,

Joe

Abstract:Conventional wisdom suggests that in order for a clock to be able to tell the time, the clock cannot be a static device, since if it were, the clock at different times would be indistinguishable. In other words, the clock must be switched on. This widely held belief is indeed true for all classical clocks. We show however, that somewhat counter-intuitively, a quantum clock can be proven to measure to arbitrary high precision how much time has passed between two events, even though it has always been off during and before these events took place. Our results use counterfactual reasoning to show that the mere fact that a clock could have been switched on  allows us to predict time even if it was never switched on in the past, present, or future. Our protocols provide fresh insight into an over 2000 year old debate regarding the nature of time | lending support for the substantival theory of time.