IMPRS monthly meeting

Title: Testing the foundations of quantum mechanics with multi-path interferometers

Time and Place: Tuesday June 18th, 10:00 a.m.; SRLP 0.179 at Staudtstr. 1

Speaker: Dr. Robert Keil (University of Innsbruck, Austria)

Organisation: Marc Pleinert (FAU/ IOIP)


Quantum mechanics in its modern formulation relies on several fundamental axioms. One of these axioms is that states of a system are represented by complex wavefunctions. Another, the Born rule, relates these wavefunction to measurable probabilities by stating that the probability density equates the squared magnitude of the wavefunction.
As it is the very nature of axioms in physics, they cannot be theoretically proven, but only tested against experiments. Interestingly, it turns out that both axioms can be tested against potential generalisations by one and the same experiment in a multi-path interferometer: Complexity of the wavefunction implies that the relative phases of all path combinations add up to zero, whereas the Born rule dictates the absence of higher-order interference with more than two contributing amplitudes. Both phenomena can be tested by measuring the output signal of an interferometer with individually blocked paths and comparing the arising interferences with each other.
In this talk, I will give an introduction into the topic and present the state of the art. The most precise experiment on the Born rule so far has been implemented via an actively stabilised five-path MachZehnder interferometer in free space. In combination with a thorough characterisation of detector nonlinearities, this allowed us to bound the magnitude of higher-order interferences relative to the usual (first-order) interference to lower than 10^(-4), which also bounds the parameters of generalised interference models.
Making statements about the complexity of the wavefunction is more subtle, however, as the applied measure is biased by a variety of effects, particularly a limited coherence in the interferometer. Therefore, we have started working towards integrated waveguide interferometers, which promise reduced footprint and superior stability. First attempts in this direction have been made and show promising results.

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