Dynamics of a qubit in a high-impedance transmission line from a bath perspective
Abstract
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.
Type
Journal articleSubject
Science & TechnologyPhysical Sciences
Optics
Physics, Atomic, Molecular & Chemical
Physics
VARIATIONAL CALCULATION
SYSTEM
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https://hdl.handle.net/10161/26457Published Version (Please cite this version)
10.1103/PhysRevA.93.033847Publication Info
Bera, S; Baranger, HU; & Florens, S (2016). Dynamics of a qubit in a high-impedance transmission line from a bath perspective.
Physical Review A, 93(3). 10.1103/PhysRevA.93.033847. Retrieved from https://hdl.handle.net/10161/26457.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Harold U. Baranger
Professor of Physics
The broad focus of Prof. Baranger's group is quantum open systems at the nanoscale,
particularly the generation of correlation between particles in such systems. Fundamental
interest in nanophysics-- the physics of small, nanometer scale, bits of solid-- stems
from the ability to control and probe systems on length scales larger than atoms but
small enough that the averaging inherent in bulk properties has not yet occurred.
Using this ability, entirely unanticipated phenomena ca

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