September 2021

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Author:
Ludovico Lami
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Given a system of massive quantum harmonic oscillators, how can we test whether their gravitational interaction is classical or quantum? Here we propose a general Gedankenexperiment to do so and benchmark it, i.e. we show how to determine the threshold beyond which one can claim that gravity behaves as a quantum interaction Hamiltonian instead of a classical field. The remarkable aspect of our approach is that it bypasses completely the problem of how a classical gravitational field may interact with the quantum oscillators. Using a delightfully simple trick from quantum information, we are able to give a bound that applies to all physically conceivable scenarios at once. We find that in a certain regime the best classical strategy introduces an error that grows linearly with time, with a coefficient that depends on the geometry of the system.

 
 
 
 
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Author:
Simon Morelli
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Entanglement shared among multiple parties presents complex challenges for the characterisation of different types of entanglement. One of the most basic insights is the fact that some mixed states can feature entanglement across every possible cut of a multipartite system, yet can be produced via a mixture of partially separable states. To distinguish states that genuinely cannot be produced from mixing partially separable states, the term genuine multipartite entanglement was coined. All these considerations originate in a paradigm where only a single copy of the state is distributed and locally acted upon. In contrast, advances in quantum technologies prompt the question of how this picture changes when multiple copies of the same state become locally accessible. Here we show that multiple copies unlock genuine multipartite entanglement from partially separable states, even from undistillable ensembles, and even more than two copies can be required to observe this effect. With these findings, we characterise the notion of partial separability in the paradigm of multiple copies and conjecture a strict hierarchy of activatable states and an asymptotic collapse of hierarchy. https://arxiv.org/abs/2106.01372

 

 
 
 
 
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Author:
Matt Hoogsteder Riera
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Metrics between quantum states all share the property that they are calculated relying only on the vectorial structure of the space. This makes it so other potentially interesting properties of the states, such as energy, are ignored in these distinguishability measures. We aim to characterise a distance between quantum states that can take into account such properties. To this purpose, we are trying to extend the concept of transport metrics from probability distributions to density matrices. This rises some problems and questions that we aim to solve. In this talk, I will briefly explain the topic of both classical and quantum transport. I will explain our motivations and objectives as well as our latest attempts at fulfiling these objectives.

 
 
 
 
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