arXiv subjects

Rajesh Asapanna

Publications and source records attributed to Rajesh Asapanna.

3 recordsLinked to original sources

arXiv2026

Accessing Chern Numbers From Bloch Eigenstates Singularities

We propose two methods to extract the Chern numbers of the Bloch bands of a two dimensional insulator, and apply them to a photonic lattice experiment. These two methods require the knowledge of the complex-valued components of the Bloch eigenvectors, or their ratios. Unlike other tomography methods relying on the approximate reconstruction of the Berry curvature and its integration over the Brillouin zone, our methods boil down to the observation of phase vorticities in the eigensates structure. Those measurements, robust to experimental noise, yield exactly quantized values. One of the two methods exploits the non-normalization of the eigenmodes, making it particularly relevant for classical wave systems.

cond-mat.mes-hall↗

arXiv2026

Decoherence-free subspaces in the noisy dynamics of discrete-step quantum walks in a photonic lattice

We study the noisy dynamics of periodically driven, discrete-step quantum walks in a one-dimensional photonic lattice. We find that in the bulk, temporal noise that is constant within a Floquet period leads to decoherence-free momentum subspaces, whereas fully random noise destroys coherence in a few time steps. When considering topological edge states, we observe decoherence no matter the type of temporal noise. To explain these results, we derive a non-perturbative master equation to describe the system's dynamics. We experimentally confirm our findings in a time multiplexed photonic lattice implemented in a double-fiber ring setup subject to laser pulse input states, in which we engineer different types of temporal noise.

quant-ph↗

arXiv2024

Observation of extrinsic topological phases in Floquet photonic lattices

Discrete-step walks describe the dynamics of particles in a lattice subject to hopping or splitting events at discrete times. Despite being of primordial interest to the physics of quantum walks, the topological properties arising from their discrete-step nature have been hardly explored. Here we report the observation of topological phases unique to discrete-step walks. We use light pulses in a double-fibre ring setup whose dynamics maps into a two-dimensional lattice subject to discrete splitting events. We show that the number of edge states is not simply described by the bulk invariants of the lattice (i.e., the Chern number and the Floquet winding number) as would be the case in static lattices and in lattices subject to smooth modulations. The number of edge states is also determined by a topological invariant associated to the discrete-step unitary operators acting at the edges of the lattice. This situation goes beyond the usual bulk-edge correspondence and allows manipulating the number of edge states without the need to go through a gap closing transition. Our work opens new perspectives for the engineering of topological modes for particles subject to quantum walks.

quant-ph↗