Condensed Matter Seminar Series

Emerging Nonadiabatic Wavefunction in Strongly Coupled Qubits

Soumya Bera

Institut Neel, Grenoble France

Thursday Feb 27,  11:30 am,  Room 298,  Physics Building

Abstract: In nature real systems are coupled to a large number of macroscopic degrees of freedom which play an important role in determining their phase coherence. To understand the role of the environment it is customary to begin with a simple model of a qubit (two level system) coupled with an infinite number of quantum oscillators (bosons). While the weak coupling limit of this model is well understood by using perturbative approaches, a complete analytical theory beyond the perturbation theory still needs to be addressed. In this work we present a generalized variational coherent state ansatz for the ground state of the qubit-photon system, which is supported by constructing quantum tomography of the states using Numerical Renormalization Group calculations. We show that at strong coupling the ground state wave-function of the joint spin-boson system is highly entangled with emerging non-adiabatic features (Schrodinger cat like states of the environment). The Wigner distributions of the bosonic wave-function projected in different spin sectors support this strongly non-adiabatic nature of the wave-function. Furthermore, we calculate the entanglement entropy of the spin and a single bosonic mode subsystem. The joint entropy shows a peak structure around the Kondo scale, which further confirms the non-polaronic effect in the ground state wave-function.