Universiteit Leiden

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Proefschrift

Smoothly breaking unitarity : studying spontaneous collapse using two entangled, tuneable, coherent amplifiers

The Copenhagen interpretation of quantum mechanics states that a measurement collapses a wavefunction onto an eigenstate of the corresponding measurement operator.

Auteur
Reep, T.H.A. van der
Datum
13 juni 2019
Links
Thesis in Leiden Repository

The Copenhagen interpretation of quantum mechanics states that a measurement collapses a wavefunction onto an eigenstate of the corresponding measurement operator. This causes a quantum mechanical wavefunction to break its unitary evolution described by the Schrödinger equation and is the source of the quantum measurement problem. In this thesis we take the first steps to an experiment that might shed light on this century-old problem. We envision a single-microwave-photon interferometer that has a travelling-wave parametric amplifier (TWPA) added to each of its arms. We wonder if the process of amplification of the quantum state causes the wavefunction to collapse, as it might turn into a detector while smoothly increasing the amplifier's gain. To this end we introduce necessary concepts from the field of microwave engineering. Then, we develop a quantum theory to describe TWPAs. This is followed by preliminary calculations on the expected interference visibility of the envisioned interferometer as a function of amplifier gain and losses. Furthermore, we describe how wavefunction collapse might reveal itself in the experimental results. Finally, the thesis describes our efforts to develop a low-loss TWPA based on Josephson junctions.

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