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Emerging non-adiabatic wavefunction in strongly dissipative qubits

Soumya Bera, Institut Neel, CNRS, Grenoble

22.11.2013 at 10:15 


In nature real systems are coupled to a large number of macroscopic degrees of freedom which plays an important role in determining their coherence properties. To understand the role of environment it is customary to begin with a simple model of a qubit (two level system) coupled with 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 need 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 environment). The Wigner distributions of the bosonic wave-function projected in different spin sectors support this strong 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 Kondo scale, which further confirms the non-polaronic effect in the ground state wave-function.

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