Theory Seminar - Jacob Barandes

On Monday, Oct. 6, at 1 p.m., Jacob Barandes of Harvard University will present "Probability, Indivisibility and Quantum Theory" via Zoom. The seminar will be livestreamed in CEBAF Center rm. L102.

Abstract: In textbooks, quantum theory is usually defined in terms of a complicated collection of abstract mathematical ingredients, such as wave functions, Hilbert spaces and self-adjoint operators. One then plugs these ingredients into special formulas that produce probabilities that we can verify with laboratory measurements. But the axioms of the textbook theory do not explain why these special formulas are true, nor how probabilities emerge from them. The axioms also exhibit various ambiguities and gaps, the most famous of which is known as “the measurement problem.”

Quantum foundations is an area of research devoted to studying and resolving these sorts of problems. Over the past century, these efforts have produced a remarkable number of important spinoffs, including entanglement, decoherence, quantum advantage and the Bell inequality (which led to the 2022 Nobel Prize in Physics). It would be an understatement to say that a large fraction of current research in physics relies on these spinoffs.

In this talk, I will describe a novel approach to quantum foundations based on a newly discovered correspondence between quantum systems and “indivisible” stochastic processes. After explaining what indivisible stochastic processes are, starting from their first appearance in the research literature in 2021, I will show how to use this correspondence to reconstruct quantum theory in terms of ordinary notions of probability playing out through a classical picture of the world. The resulting indivisible formulation of quantum theory does not include wave functions or Hilbert spaces among its physical objects, nor does it involve parallel universes, pilot waves, alive-and-dead cats or other famously exotic ingredients.

The indivisible theory makes the world safe for ordinary probability theory, potentially opens the door to new generalizations of quantum theory, and suggests that quantum theory and quantum computers might provide more efficient techniques for simulating stochastic processes beyond the Markov approximation, with potential applications for statistical modeling, finance, neuroscience, ecology and other areas.