Non Gaussian States and Operations

In recent years the role of state generation using large interferometers and non classical light has become increasingly popular. This is due to these optical networks’ ability to enable a wide range of applications which range from quantum computing and sensing to advanced communication systems. Although recently fully programmable photonic chips have allowed for implementations of interferometers of up to 10 modes but any large scale implementations are hampered due to losses and a steeply increasing number of optical components.
The work in this thesis is oriented towards exploring and experimentally demonstrating highly scalable, low-loss multimode squeezed light interferometer schemes and parametric Gaussian states, exploiting measurement-induced operations to realize very large interferometers accurately although at the cost of decreased programmability. We validate our approach experimentally first through a 6-mode interferometer and subsequently showcase its scalability by extending the design to 400 modes and demonstrating large Haar random interferometers with very high precision.
Subsequent sections then deviate from Gaussian states and focus on degaussifying the discussed parametric Gaussian states in order to control and generate various interesting non-Gaussian states. In particular we also discuss the generation of some exotic multi-photon subtracted states and breeding schemes that can utilized to generate some highly coveted grid states.
We then discuss and evaluate entanglement beyond the Gaussian context. The currently used entanglement test often fail to detect quantum entanglement in non-Gaussian states. While entanglement in non-Gaussian states can be detected by performing a tomography of the Wigner function, these methods are computationally heavy and are are very expensive to perform in terms of resources. To this end we first theoretically derive, analytically and numerically test and then experimentally demonstrate an inseparability criterion that out-performs its currently known and used counterparts for two party two mode states.