This series consists of talks in the area of Foundations of Quantum Theory. Seminar and group meetings will alternate.
While spacetime and quantum theory are crucial parts of modern theoretical physics, the problem of quantum gravity demonstrates that their full relationship is not yet completely understood. In my talk, I report on two recent results that aim to shed light on this relationship via ideas and tools from quantum foundations.
Consistent dynamics which couples classical and quantum systems exists, provided it is stochastic. This provides a way to
study the back-reaction of quantum systems on classical ones and has recently been explored in the context of quantum fields back-reacting
I will introduce a tool to construct self-testing Bell inequalities from the stabiliser formalism and present two applications in the framework of device-independent certification protocols. Firstly, I will show how the method allows to derive Bell inequalities maximally violated by the family of multi-qubit graph states and suited for their robust self-testing.
We often say that quantum mechanics allows to calculate the probability of future events. In fact, quantum mechanics does not discriminate between predicting the future or postdicting the past. I will present the results of a recent work by Rovelli, Donà and me, where we address the apparent tension between the time symmetry of elementary quantum mechanics and the intrinsic time orientation of the formulations of quantum theory used in the quantum information and foundations communities.
In recent years, it has become increasingly well-known that nearly all the major no-go theorems in quantum foundations can be circumvented by violating a single assumption: the hidden variables (that determine the outcomes) are uncorrelated with the measurement settings. A hidden-variable theory that violates this assumption can be local, separable, non-contextual and have an epistemic quantum state. Such a theory would be particularly well-suited to relativistic contexts. Are such theories actually feasible?
A priori, there exists no preferential temporal direction as microscopic physical laws are time-symmetric. Still, the second law of thermodynamics allows one to associate the 'forward' temporal direction to a positive variation of the total entropy produced in a thermodynamic process, and a negative variation with its 'time-reversal' counterpart.
A proposal is made for a fundamental theory, in which the history of the universe is constituted of views of itself. Views are attributes of events, and the theory's only be-ables; they comprise information about energy and momentum transferred to an event from its causal past.
Using a process-theoretic formalism, we introduce the notion of a causal-inferential theory: a triple consisting of a theory of causal influences, a theory of inferences (of both the Boolean and Bayesian varieties), and a specification of how these interact. Recasting the notions of operational and realist theories in this mold clarifies what a realist account of an experiment offers beyond an operational account.
The compatibility-hypergraph approach to contextuality (CA) and the contextuality-by-default approach (CbD) are usually presented as products of entirely different views on how physical measurements and measurement contexts should be understood: the latter is based on the idea that a physical measurement has to be seen by a collection of random variables, one for each context containing that measurement, while the imposition of the non-disturbance condition as a physical requirement in the former precludes such interpretation of measurements.
To analyze the performance of adaptive measurement protocols for the detection and quanti cation of state resources, we introduce the framework of quantum preparation games. A preparation game is a task whereby a player sequentially sends a number of quantum states to a referee, who probes each of them and announces the measurement result. The measurement setting at each round, as well as the final score of the game, are decided by the referee based on the past history of settings and measurement outcomes.