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Cavity quantum phonon dynamics

Periodic Report Summary 2 - CAVITYQPD (Cavity quantum phonon dynamics)

According to the Heisenberg uncertainty principle in quantum mechanics, the position and momentum of a particle cannot be well defined at a given instant of time. However, in so-called squeezed quantum state, one of them can be very well defined. We have achieved this kind of quantum state for a nearly macroscopic system, that is, a vibrating micromechanical drum.

Besides that the position and momentum of a particle cannot exist well-defined the same time, an observer cannot simultaneously obtain accurate information of both of them. This principle sets a fundamental limit to any measurement. In quantum mechanics even electromagnetic waves can be represented by particles, photons, and thus their detection is subject to the uncertainty principle. Without any uncertainties, even faintest signals could be measured and for example mobile phone network would operate anywhere in the world with a single access point.

For radio- and microwaves used in telecommunication, the measurement uncertainties result from the technical imperfections. They pose much more serious limitations to the measurement of signals than the quantum limit. However, quantum limit of microwave measurement has so far been reached with superconducting circuits used in quantum computing.

In the project we have devised various approaches for sensitive measurements using novel techniques involving nanodrums. Our measurements even go beyond the quantum limit. For the particle this would be possible by measuring only either the position or momentum, and completely discarding the information about the other property. For a light wave, accessing only part of the wave and discarding the information in the other part realizes an analogous measurement. It can be used in accessing tiny signals for example in quantum computing and perhaps also in measurement of gravitational waves.