arXiv subjects

Poornima Shakya

Publications and source records attributed to Poornima Shakya.

3 recordsLinked to original sources

arXiv2025

Shot noise as a probe for Andreev reflection in graphene-based heterojunctions

Shot noise emerges due to the discrete nature of charge transport and provides direct access to the underlying microscopic transport mechanisms governing current flow in mesoscopic conductors. In this work, we demonstrate that quantum shot noise offers a direct and robust fingerprint of Andreev reflection, distinguishing between retro and specular processes in graphene-superconductor, graphene-superconductor-graphene, and superconductor-graphene-superconductor junctions. At the graphene-superconductor interface, exact reflection amplitudes obtained from full wavefunction matching within the Bogoliubov-de Gennes formalism capture retro and specular regimes. The associated Fano factor exhibits distinct Fermi-level-dependent signatures, with retro Andreev reflection suppressing and specular Andreev reflection enhancing the shot noise. Extensions to graphene-superconductor-graphene and superconductor-graphene-superconductor configurations reveal how the transmission spectrum and, consequently, the noise profile are modified in the presence of multiple interfaces, coherent quasiparticle interference, and superconducting phase variations. Our findings establish shot noise spectroscopy as a potent and experimentally viable probe for differentiating Andreev reflection types in graphene-based quantum devices, providing complementary insights beyond conventional conductance measurements.

cond-mat.mes-hall↗

arXiv2024

Generation, manipulation and detection of snake state trajectories of a neutral atom in a ring-cavity

We propose a set-up to create and detect the atomic counterpart of snake state trajectories which occur at the interface where the magnetic field reverses direction. Such a magnetic field is generated by coupling two counter-propagating modes of a ring cavity to a two-level atom. The spatial distribution and the strength of the induced magnetic field are controlled by the transverse mode profile of the cavity modes and the number of photons in the two modes, respectively. By analysing the atomic motion in such a magnetic field while including the cavity back-action, we find that the atom follows snake state trajectories which can be non-destructively detected and reconstructed from the phase and the intensity of the light field leaking from the cavity. We finally show that the system parameters can be tuned to modify the transport properties of the snake states and even amplify the effect of cavity feedback which can completely alter their topology.

cond-mat.quant-gas↗

arXiv2023

Dimensional crossover in self-organised super-radiant phases of ultra cold atoms inside a cavity

We consider a condensate of ultra cold bosonic atoms in a linear optical cavity illuminated by a two-pump configuration where each pump is making different angles with the direction of the cavity axis. We show such configuration allows a smooth transition from a one-dimensional quantum optical lattice configuration to a two-dimensional quantum optical lattice configuration induced by the cavity-atom interaction. Using a Holstein-Primakoff transformation, we find out the atomic density profile of such self-organised ground state in the super-radiant phase as a function of the angular orientations of the pump in such dynamical quantum optical lattice, and, also provide an analysis of their structures in coordinate and momentum space. In the later part of the paper, we show how the corresponding results can also be qualitatively understood in terms of an Extended Bose-Hubbard model in such quantum optical lattice potential.

cond-mat.quant-gas↗