Quantum Foundations Podcast

If there really is a quantum reality for every possible outcome of a measurement, then where do measurement probabilities come from? Dr Tony Short at the University of Bristol has used a set of intuitive assumptions to derive probability in a quantum multiverse. In this episode we discuss his motivations for exploring the many-worlds interpretation; what his assumptions are and how they lead to the Born rule for measurement probabilities; and how these ideas fit within the broader landscape of research in quantum foundations, probability and the many-worlds interpretation.

The notion of true quantum nonlocality is absurd. Prof Tim Palmer from the University of Oxford suggests that there is a hidden assumption in standard quantum mechanics, and dropping it will save us from this absurdity. Namely, the reality of counterfactuals: the physics of what could have happened but did not. Inspired by chaos theory and the fractal structure widespread in atmospheric physics, Palmer has developed a new underlying structure for quantum theory, with radical implications for our fundamental principles of quantum physics; the limits of quantum computation; and perhaps even the search for quantum gravity.

What if you could put an observer in superposition on a quantum computer? Dr Will Zeng suggests that this experiment could stretch standard quantum theory so far that it might break — and radically update our understanding of physical reality. However, today's proof-of-principle experiments on quantum computers use single qubits to model observers. Zeng explains how a new programme of research aims to quantify "observer-ness" and conduct experiments with increasingly realistic observers, pushing quantum computers to the limits until they can run actual quantum Artificial General Intelligence experiments.

Our most far-reaching principles of physics are not about what changes, but what stays the same: conservation laws. In this episode of the Quantum Foundations Podcast, Dr Chiara Marletto from the University of Oxford explains how such principles enable discovery of new physical phenomena; their central role in thermodynamics; controversies about how they hold up in quantum mechanics; and how they can be used to formulate results about future theories of physics beyond quantum.

You’ve heard of cryptography. Perhaps quantum cryptography too. Maybe even post-quantum cryptography. But what about *quantum post-quantum cryptography*?! When this came up in conversation with Oxford Computer Scientist Matthew Gray recently, I’d never heard of it. I wanted to know more, so I invited him for a podcast. Turns out, there’s a whole world of layers to unravel linking quantum and cryptography — or even multiple worlds… In this discussion, we dip into those, and how this all relates to “metacomplexity” problems: the hardness of figuring out the hardness of a problem. Listen to this episode if you want to experience your perception of how quantum computing meets cryptography shift from monochrome to technicolour, as we push cryptography to its limits through the lens of fundamental assumptions about computation, quantum physics and reality.