Abstract for Talk 1:

It was once thought that if a probe quantum state exhibits high sensitivity to a particular transformation, this must come with the cost of decreased sensitivity to other transformations generated by non-commuting observables. However, particular classes of states exist that disprove this misconception, for example the “compass state” and, more recently, generation of the “tetrahedron state” was carried out in our group. The tetrahedron state is created in the symmetric subspace of four optical photons’ polarisation, and exhibits maximal sensitivity to arbitrary SU(2) rotations. In this presentation, I will talk about two quantum parameter estimation experiments, starting with the experimental generation of the tetrahedron state, the optimal four-photon state for estimating rotations. I will then discuss the experimental generation of the optimal two-photon state for simultaneous estimation of the parameters describing a rotation.

Abstract for Talk 2:

The one-dimensional p-wave superconductor with boundary Majorana modes has attracted theoretical and experimental interest due to its potential application in topological quantum computation. Spin-1/2 Kitaev ladder systems with bond-dependent Ising interactions, featuring Majorana fermions coupled with Z_2 flux, can also exhibit boundary Majorana modes when they are in a topological phase. However, due to the ground state degeneracy, a superposition of the two states may annihilate the Majorana modes. Here we demonstrate a projective measurement that selects one of the degenerate Z_2 sectors, enabling the emergence of Majorana modes. We present the phase diagram across different flux configurations and interaction strengths using analytical and numerical analysis. Our study illustrates the appearance of Majorana modes at the interfaces of topological and non-topological phases, with each corresponding to different flux sectors for a given interaction strength. These modes, along with boundary Majorana modes, can be manipulated and fused by tuning the flux sectors achievable through applying local spin operators. We discuss the engineering of a trimmed Kitaev honeycomb ladder, along with its phase diagram and open questions for future studies.