51 research outputs found
Scattering of two photons from two distant qubits: Exact solution
We consider the inelastic scattering of two photons from two qubits separated
by an arbitrary distance and coupled to a one-dimensional transmission
line. We present an exact, analytical solution to the problem, and use it to
explore a particular configuration of qubits which is transparent to
single-photon scattering, thus highlighting non-Markovian effects of inelastic
two-photon scattering: Strong two-photon interference and momentum dependent
photon (anti-)bunching. This latter effect can be seen as an inelastic
generalization of the Hong--Ou--Mandel effect.Comment: 5 pages + 11 pages in the supplement, v2: published versio
Quantum theory of light scattering in a one-dimensional channel: Interaction effect on photon statistics and entanglement entropy
We provide a complete and exact quantum description of coherent light
scattering in a one-dimensional multi-mode transmission line coupled to a
two-level emitter. Using recently developed scattering approach we discuss
transmission properties, power spectrum, the full counting statistics and the
entanglement entropy of transmitted and reflected states of light. Our approach
takes into account spatial parameters of an incident coherent pulse as well as
waiting and counting times of a detector. We describe time evolution of the
power spectrum as well as observe deviations from the Poissonian statistics for
reflected and transmitted fields. In particular, the statistics of reflected
photons can change from sub-Poissonian to super-Poissonian for increasing
values of the detuning, while the statistics of transmitted photons is strictly
super-Poissonian in all parametric regimes. We study the entanglement entropy
of some spatial part of the scattered pulse and observe that it obeys the area
laws and that it is bounded by the maximal entropy of the effective four-level
system.Comment: 22 pages, 6 figures; discussion extended, references adde
Relaxation vs decoherence: Spin and current dynamics in the anisotropic Kondo model at finite bias and magnetic field
Using a nonequilibrium renormalization group method we study the real-time
evolution of spin and current in the anisotropic Kondo model (both
antiferromagnetic and ferromagnetic) at finite magnetic field and bias
voltage . We derive analytic expressions for all times in the weak-coupling
regime ( strong coupling scale). We find that
all observables decay both with the spin relaxation and decoherence rates
. Various -dependent logarithmic, oscillatory, and power-law
contributions are predicted. The low-energy cutoff of logarithmic terms is
generically identified by the difference of transport decay rates. For small
times , we obtain universal dynamics for spin and
current
Topologically protected strongly-correlated states of photons
Hybrid photonic nanostructures allow the engineering of novel interesting
states of light. One recent example is topological photonic crystals where a
nontrivial Berry phase of the photonic band structure gives rise to
topologically protected unidirectionally-propagating (chiral) edge states of
photons. Here we demonstrate that by coupling an array of emitters to the
chiral photonic edge state one can create strongly correlated states of photons
in a highly controllable way. These are topologically protected and have a
number of remarkable universal properties: The outcome of scattering does not
depend on the positions of emitters and is given only by universal numbers, the
zeroes of Laguerre polynomials; two-photon correlation functions manifest a
well-pronounced even-odd effect with respect to the number of emitters, and the
result of scattering is robust with respect to fluctuations in the emitters'
transition frequencies.Comment: 23 pages, 4 figure
Kondo model in nonequilibrium: Interplay between voltage, temperature, and crossover from weak to strong coupling
We consider an open quantum system in contact with fermionic metallic
reservoirs in a nonequilibrium setup. For the case of spin, orbital or
potential fluctuations, we present a systematic formulation of real-time
renormalization group at finite temperature, where the complex Fourier variable
of an effective Liouvillian is used as flow parameter. We derive a universal
set of differential equations free of divergencies written as a systematic
power series in terms of the frequency-independent two-point vertex only, and
solve it in different truncation orders by using a universal set of boundary
conditions. We apply the formalism to the description of the weak to strong
coupling crossover of the isotropic spin-1/2 nonequilibrium Kondo model at zero
magnetic field. From the temperature and voltage dependence of the conductance
in different energy regimes we determine various characteristic low-energy
scales and compare their universal ratio to known results. For a fixed finite
bias voltage larger than the Kondo temperature, we find that the
temperature-dependence of the differential conductance exhibits non-monotonic
behavior in the form of a peak structure. We show that the peak position and
peak width scale linearly with the applied voltage over many orders of
magnitude in units of the Kondo temperature. Finally, we compare our
calculations with recent experiments.Comment: 48 pages, 10 figure
Supersymmetry in quantum optics and in spin-orbit coupled systems
Light-matter interaction is naturally described by coupled bosonic and
fermionic subsystems. This suggests that a certain Bose-Fermi duality is
naturally present in the fundamental quantum mechanical description of photons
interacting with atoms. We reveal submanifolds in parameter space of a basic
light-matter interacting system where this duality is promoted to a
supersymmetry (SUSY) which remains unbroken. We show that SUSY is robust with
respect to decoherence and dissipation. In particular, a stationary density
matrix at the supersymmetric lines in the parameter space has a degenerate
subspace. A dimension of this subspace is given by the Witten index and thus
topologically protected. As a consequence of this SUSY, dissipative dynamics at
the supersymmetric lines is constrained by an additional conserved quantity
which translates some part of information about an initial state into the
stationary state subspace. We also demonstrate a robustness of this additional
conserved quantity away from the supersymmetric lines. In addition, we
demonstrate that the same SUSY structures are present in condensed matter
systems with spin-orbit couplings of Rashba and Dresselhaus types, and
therefore spin-orbit coupled systems at the SUSY lines should be robust with
respect to various types of disorder and decoherences. Our findings suggest
that optical and condensed matter systems at the SUSY points can be used for
quantum information technology and can open an avenue for quantum simulation of
the SUSY field theories.Comment: 15 pages, 3 figure
Control over few photon pulses by a time-periodic modulation of the photon-emitter coupling
We develop a Floquet scattering formalism for the description of
quasistationary states of microwave photons in a one-dimensional waveguide
interacting with a nonlinear cavity by means of a periodically modulated
coupling. This model is inspired by the recent progress in engineering of
tunable coupling schemes with superconducting qubits. We argue that our model
can realize the quantum analogue of an optical chopper. We find strong periodic
modulations of the transmission and reflection envelopes in the scattered
few-photon pulses, including photon compression and blockade, as well as
dramatic changes in statistics. Our theoretical analysis allows us to explain
these non-trivial phenomena as arising from non-adiabatic memory effects.Comment: 12 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1603.0549
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