Special CPM Seminar

Testing the reality of the quantum wavefunction

Stephanie Simmons

Department of Physics
Simon Fraser University

Is a quantum wavefunction exclusively an abstract mathematical tool - perhaps something which encodes our knowledge of a quantum system? Or is the quantum wavefunction instead a concrete physical entity which exists in reality? Until fairly recently it seemed like the answers to such epistemic/ontic questions could not be provided experimentally. Surprisingly, the Pusey-Barrett-Rudolph test, further developed by Barrett-Cavalcanti-Lal-Maroney (‘BCLM’) and later Branciard, offers an experimental avenue to rule out ‘maximally psi-epistemic’ models of quantum mechanics. Here we report a successful (2.8 sigma) demonstration of the BCLM/Branciard test, free from the fair sampling loophole, which indicates that the quantum wavefunction cannot be purely a state of knowledge. To accomplish this we employed a single electron-nuclear two spin system in isotopically purified silicon. We identified and removed the dominant remaining sources of initialisation and measurement error in this system to achieve a simultaneous >99.9% fidelity for each of initialisation, manipulation and readout. Such a high degree of perfection is required to successfully perform the BCLM test, and also to surpass a number of modern quantum error correction thresholds.