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Dynamics of a qubit in a high-impedance transmission line from a bath perspective

Publication ,  Journal Article
Bera, S; Baranger, HU; Florens, S
Published in: Physical Review A
March 28, 2016

We investigate the quantum dynamics of a generic model of light-matter interaction in the context of high-impedance waveguides, focusing on the behavior of the photonic states generated in the waveguide. The model treated consists simply of a two-level system coupled to a bosonic bath (the Ohmic spin-boson model). Quantum quenches as well as scattering of an incident coherent pulse are studied using two complementary methods. First, we develop an approximate ansatz for the electromagnetic waves based on a single multimode coherent state wave function; formally, this approach combines in a single framework ideas from adiabatic renormalization, the Born-Markov approximation, and input-output theory. Second, we present numerically exact results for scattering of a weak intensity pulse by using numerical renormalization group (NRG) calculations. NRG provides a benchmark for any linear response property throughout the ultrastrong-coupling regime. We find that in a sudden quantum quench, the coherent state approach produces physical artifacts, such as improper relaxation to the steady state. These previously unnoticed problems are related to the simplified form of the ansatz that generates spurious correlations within the bath. In the scattering problem, NRG is used to find the transmission and reflection of a single photon, as well as the inelastic scattering of that single photon. Simple analytical formulas are established and tested against the NRG data that predict quantitatively the transport coefficients for up to moderate environmental impedance. These formulas resolve pending issues regarding the presence of inelastic losses in the spin-boson model near absorption resonances, and could be used for comparison to experiments in Josephson waveguide quantum electrodynamics. Finally, the scattering results using the coherent state wave-function approach are compared favorably to the NRG results for very weak incident intensity. We end our study by presenting results at higher power where the response of the system is nonlinear.

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Published In

Physical Review A

DOI

EISSN

2469-9934

ISSN

2469-9926

Publication Date

March 28, 2016

Volume

93

Issue

3

Related Subject Headings

  • 51 Physical sciences
  • 49 Mathematical sciences
  • 34 Chemical sciences
 

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Bera, S., Baranger, H. U., & Florens, S. (2016). Dynamics of a qubit in a high-impedance transmission line from a bath perspective. Physical Review A, 93(3). https://doi.org/10.1103/PhysRevA.93.033847
Bera, S., H. U. Baranger, and S. Florens. “Dynamics of a qubit in a high-impedance transmission line from a bath perspective.” Physical Review A 93, no. 3 (March 28, 2016). https://doi.org/10.1103/PhysRevA.93.033847.
Bera S, Baranger HU, Florens S. Dynamics of a qubit in a high-impedance transmission line from a bath perspective. Physical Review A. 2016 Mar 28;93(3).
Bera, S., et al. “Dynamics of a qubit in a high-impedance transmission line from a bath perspective.” Physical Review A, vol. 93, no. 3, Mar. 2016. Scopus, doi:10.1103/PhysRevA.93.033847.
Bera S, Baranger HU, Florens S. Dynamics of a qubit in a high-impedance transmission line from a bath perspective. Physical Review A. 2016 Mar 28;93(3).

Published In

Physical Review A

DOI

EISSN

2469-9934

ISSN

2469-9926

Publication Date

March 28, 2016

Volume

93

Issue

3

Related Subject Headings

  • 51 Physical sciences
  • 49 Mathematical sciences
  • 34 Chemical sciences