This Week's Discoveries | 12 May 2020
- Tuesday 12 May 2020
- Kaltura Live Room
What is a measurement?
What is a measurement? Crossing over from the quantum world to the classical world and back
Tjerk Oosterkamp (LION)
Tjerk is professor of Experimental Physics in de Quantum Matter and Optics group at LION.
Quantum mechanics led to a revolution in our understanding of nature and in practical applications. Despite this progress, there remains the question of how the classical world emerges from the underlying quantum physics. Some people even say there isn't really a classical world, and prefer to talk about many parallel universes, in which superpositions remain forever.
Textbooks on quantum mechanics typically repeat the postulate made by Von Neumann that measurement occurs when a quantum state interacts with a classical measurement machine, and results in a probabilistic measurement outcome. Exactly how this postulate should be implemented has been at the center of debates ever since its formulation, and led to various theoretical proposals for an underlying dynamical description, in terms of either interactions with thus far undetected properties of the vacuum environment, or of fundamental nonlinear corrections to Schrödinger’s equation.
With a recently granted ENW-Groot grant, we (Dirk Bouwmeester, Jasper van Wezel [UvA] and Tjerk Oosterkamp) aim to approach this outstanding problem, by providing experimental input coming from both the microscopic and macroscopic sides. At the quantum level, we aim to scale up the mass and/or displacements associated to quantum superposition states and measure their dynamics by highly controlled interactions with the surrounding. Coming from the classical side, we will cool down mechanical resonators that are in thermal equilibrium with their environment at a well-defined temperature, but are only weakly coupled to the thermal bath.
We aim to improve these experiments so that we can measure the slight deviations in temperature between the resonator and its bath, that are predicted to arise from changes in entanglement entropy during measurement. Both approaches will result in experimental constraints on various theoretical proposals for the dynamics of quantum measurement, and possibly on an experimental demarcation of what constitutes a quantum measurement.