Masters Thesis defence by Christian Anker Rosiek

Enhancing the Formation of Wigner Negativity in a Kerr Oscillator via Quadrature Squeezing


Quantum mechanics is a well-established theory which describes the world at microscopic scales. Yet the classical laws of physics are comfortably able to explain most macroscopic phenomena that we observe. An important part of research into quantum mechanics is pushing the size of quantum systems to better understand this transition. The Wigner function can be used to describe the state of a quantum system
and in turn calculate probabilities of the system. It differs from an ordinary probability distribution though, since it can take on negative values. This ability can be used to establish a hierarchy of quantum states in order of increasing nonclassicality. The possibility of observing negative states in larger quantum systems is however currently severely limited by decoherence effects such as damping and dephasing present in  hese systems. Identifying a way to reduce these effects is therefore of great benefit to the future experiments within the field of quantum science. Motivated by experiments with nanomechanical systems, the evolution of a Kerr oscillator with specific focus on creation of states with a negative Wigner function is investigated. Results are presented that demonstrate an asymptotic behavior in the large squeezing regime for the negativity of a squeezed vacuum state under unitary evolution. The analysis and model are extended to squeezed vacuum states of open systems, adding the decoherence effects of damping and dephasing. These effects are investigated, yielding similar asymptotic results for the behavior of these effects in the large squeezing regime. Combining these results, it is shown that a weak nonlinearity as compared to damping may be improved by increasing the squeezing of the initial state. It is also shown that this may be done without  xacerbating the effects of dephasing.