Browsing by Author "Kähärä, Jaakko"

We study the properties of flat band states of bosons and their potential for all-optical switching. Flat bands are dispersionless energy bands found in certain lattice structures. The corresponding eigenstates, called flat band states, have the unique property of being localized to a small region of the lattice. High sensitivity of flat band lattices to the effects of interactions could make them suitable for fast, energy efficient switching. We use the Bose-Hubbard model and computational methods to study multi-boson systems by simulating the time-evolution of the particle states and computing the particle currents. As the systems were small, fewer than ten bosons, the results could be computed exactly. This was done by solving the eigenstates of the system Hamiltonian using exact diagonalization. We focus on a finite-length sawtooth lattice, first simulating weakly interacting bosons initially in a flat band state. Particle current is shown to typically increase linearly with interaction strength. However, fine-tuning the hopping amplitudes and boundary potentials, particle current through the lattice is highly suppressed. We use this property to construct a switch which is turned on by pumping the input with control photons. Inclusion of particle interactions disrupts the system, resulting in a large non-linear increase in particle current. We find that certain flat band lattices could be used as medium for an optical switch capable of controlling the transport of individual photons. In practice, highly optically nonlinear materials are required to reduce the switching time which is found to be inversely proportional to the interaction strength.