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Zenith Grant Awardee

Hendrik Ulbricht

University of Southampton


Project Title

Testing quantum theory by de Broglie interference of polystyrene spheres and viruses

Project Summary

The ultimate goal of this FQXi research project is to experimentally test the macroscopic limits of quantum physics and the role of gravity as a decohering element to serve solid ground for further investigations of the foundations of modern physics. Such tests are basing on the experimental proof of the wave- like behaviour of massive particles by demonstrating quantum mechanical superposition – the most striking feature of quantum physics, the existence of states of particles being here and there at the same time. We aim to increase the actual mass limit of particles showing quantum behaviour in matter-wave interferometry by three orders of magnitude (to a mass equivalent to 106 hydrogen atoms). Until now the most massive particle, which showed interference, is an organic molecule of the mass of 3000 hydrogen atoms. Quantum mechanics still works for such molecules. Therefore still an open question is how massive a particle can be and still be described by Schroedinger's wave function within the framework of quantum mechanics. According to quantum mechanics no limits exist as 'only' Decoherence prevents us from macroscopic quantumness. Alternative theories which extend and modify the Schroedinger equation have been developed since the birth of quantum mechanics itself and are still debated.

Technical Abstract

This project addresses foundational aspects of quantum mechanics and gravity. We aim to experimentally explore the physical reason for the quantum to classical transition of massive particles. Both Decoherence models and alternative quantum theories (including semi-classical quantum gravity) giving reason for the collapse of the wave function. The theoretically proposed parameters for the collapse have to be experimentally tested. Within this project we will set up a novel particle source and interferometer for de Broglie interference of large particles as nano-spheres and viruses to do exactly this. The mass scale for the planned experiments is up to 106 amu (atomic mass units). The novelty of this approach is to utilize the nano-optical trapping of <100 nm sized particles in the so-called SIBA trap. Here the nanoaperture in a metal thin film enhances the local optical field amplitude and spatial resolution. Launched from this static trap, accelerated by Earth's gravity, an optical phase grating will act as the diffractive element to modulate the phase of the matter-waves and the particle distribution will be detected after their deposition on surfaces. This is radically new and if successful allows an increase in mass by three orders of magnitude in comparison to our actual experiments on molecule interference.

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