Fragility of the Schrödinger Cat in thermal environments

Sandip Bera; Kenny L S Yip; Sajeev John

doi:10.1038/s41598-023-45701-3

Fragility of the Schrödinger Cat in thermal environments

Sci Rep. 2023 Oct 31;13(1):18691. doi: 10.1038/s41598-023-45701-3.

Authors

Sandip Bera¹, Kenny L S Yip¹, Sajeev John²

Affiliations

¹ Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON, M5S 1A7, Canada.
² Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON, M5S 1A7, Canada. john@physics.utoronto.ca.

Abstract

We describe the decoherence instability of Schrödinger Cat states in the two-site Bose-Hubbard model with an attractive on-site interaction between particles. For N particles with onsite attractive energy U and hopping amplitude between sites t, Cat states exist for [Formula: see text] at zero temperature. However, they are increasingly unstable to small thermal fluctuations as the Cat itself is increasingly well-defined and its components become well-separated. For any given [Formula: see text], the decoherence temperature becomes smaller for large N. The loss of off-diagonal coherence peaks in the equilibrium density matrix is dominated by the thermal admixture of the first excited state of the many-body system with its ground state. Particle number fluctuations, described in the grand canonical ensemble also reduce coherence, but to a lesser degree than thermal fluctuations. The full density matrix of the Schrödinger Cat is obtained by exact numerical diagonalization of the many-body Hamiltonian and a narrow regime in the parameter space of the particle number, temperature, and U/t is identified where small Cat states may survive decoherence in a physical environment.