https://quantum-journal.org/papers/q-2024-02-27-1267/
Presentations of quantum mechanics often include a postulate that the state
of a system undergoes an instantaneous change following a measurement.
This is clearly incompatible with special and general relativity and raises
questions concerning the description of measurement in quantum field theory (QFT).
Attempts to extend measurement postulates to QFT by hand have produced
pathologies,...
It is by now well recognized that the naive application of the projection postulate on composite quantum systems can induce signalling between their constituent components, indicative of a break- down of causality in a relativistic spacetime context. Here we introduce a necessary and sufficient condition for an ideal measurement of an observable to be nonsignalling. As well as being...
The formulation of local measurement theory for QFT has recently been an active area of research. In contrast to the asymptotic measurement framework that was enshrined in QED the new proposals aim to supply a measurement framework for measurement in local spacetime regions. In the history of QFT, in parallel to the establishment of the asymptotic scattering paradigm, there is a series of...
Experimental metaphysics is the study of how empirical results can reveal facts about the fundamental nature of the world, independent of any theory. It is a field born from Bell’s 1964 theorem, and the experiments it inspired. I argue that the high frontier for the field will come from combining Bell’s 1964 paper with those of two other scientists of roughly the same era. Specifically,...
A natural response to Einstein's hole argument is that the spacetime points on a manifold have no a priori physical meaning. But if that is so, what are the experientialists trying to achieve when they conduct experiments towards macroscopic superpositions in space?
The link to the paper: https://arxiv.org/abs/2402.10267
Bell’s theorem history ran from a cold reception in the first years of its inception to a diversified plethora of scientists working on it, which included Nobel prize winners. I have coined the term quantum dissidents to portray the physicists who worked on it in its early decades. They believed, against the views shared by most physicists, that there was good physics to be done about hidden...
In his contributions to the foundations of quantum mechanics, John S. Bell turned out to be also a true natural philosopher, sensitive to the conceptual implications of physics. In my talk, I will focus on some aspects of the ideal dialogue that Bell developed with Albert Einstein and Niels Bohr, two of the main natural philosophers of the twentieth century.
https://www.nature.com/articles/s41586-022-04941-5
Quantum networks are promising tools for the implementation
of long-range quantum communication. The characterization of
quantum correlations in networks and their usefulness for
information processing is therefore central for the progress
of the field, but so far only results for small basic network
structures or pure quantum states are known.
In my talk I will discuss two topics...
Proving the nonlocality of a distribution in a general quantum network that goes beyond the Bell scenario is generally a difficult task, due to the non-convex nature of the problem. Only few examples of proven quantum nonlocality exist even in the simple triangle network. The Elegant Joint Measurement is a quantum measurement scheme that can be used to obtain an outcome distribution in the...
Understanding the fundamental nature of gravity at the interface with quantum theory is a major open question in theoretical physics. Recently, the study of gravitating quantum systems, for instance a massive quantum system prepared in a quantum superposition of positions and sourcing a gravitational field, has attracted a lot of attention: experiments are working towards realising such a...
One of the most surprising aspects of quantum theory is that it tells us that we live in a nonlocal universe in which random correlations seem to appear instantaneously between arbitrarily distant locations. This idea was completely abhorrent to Einstein, who dismissed it as "spooky action at a distance", yet the 2022 Nobel Prize in Physics was awarded for experimental demonstrations half a...
Recently, a prominent critic of the Many Worlds (MW) interpretation summarised: 'Its main shortcoming is simply this: The interpretation is completely contentless.' In my talk, I will adopt a more generous approach and ask: What if we equip the MW interpretation, specifically its central notions of 'worlds' and 'branching,' with physical content? I will then present a no-go theorem, asserting...
The measurement postulate of quantum theory stands in conflict with the laws of thermodynamics and has evoked debate regarding what actually constitutes a measurement. With the help of modern quantum statistical mechanics, we take some first steps in formalising the hypothesis that quantum measurements are driven by the natural tendency of closed systems to maximize entropy. In this paradigm,...
The standard method for detecting entanglement and steering is via measuring suitable witness operators. This requires that some prescribed measurements are performed on the local systems. I discuss what happens when the assumption of perfect measurements no longer is employed but instead the measurements are allowed to have tiny imprecisions. I argue that small specific imprecisions can give...
