3,993 research outputs found
Kondo Resonance of a Microwave Photon
We emulate renormalization group models, such as the Spin-Boson Hamiltonian
or the anisotropic Kondo model, from a quantum optics perspective by
considering a superconducting device. The infra-red confinement involves photon
excitations of two tunable transmission lines entangled to an artificial
spin-1/2 particle or double-island charge qubit. Focusing on the propagation of
microwave light, in the underdamped regime of the Spin-Boson model, we identify
a many-body resonance where a photon is absorbed at the renormalized qubit
frequency and reemitted forward in an elastic manner. We also show that
asymptotic freedom of microwave light is reached by increasing the input signal
amplitude at low temperatures which allows the disappearance of the
transmission peak.Comment: Final Version: Main text and Supplementary Materia
Shot Noise in SU(N) Quantum Dot Kondo Effects
We study shot noise in the current of quantum dots whose low-energy behaviour
corresponds to an SU(N) Kondo model, focusing on the case N=4 relevant to
carbon nanotube dots. For general N, two-particle Fermi liquid interactions
have two distinct effects: they can enhance the noise via back-scattering
processes with an N-dependent effective charge, and can also modify the
coherent partition noise already present without interactions. For N=4, in
contrast to the SU(2) case, interactions enhance shot noise solely through an
enhancement of partition noise. This leads to a non-trivial prediction for
experiment.Comment: 4+ pages; error in numerical prefactor describing interaction effect
on noise correcte
Neutral scalar Higgs bosons in the USSM at the LHC
We study the possibility of discovering neutral scalar Higgs bosons in the
-extended supersymmetric standard model (USSM) at the CERN Large Hadron
Collider (LHC), by examining their productions via the exotic quark loop in the
gluon fusion process at leading order. It is possible in some parameter region
that the neutral scalar Higgs bosons may have stronger couplings with the
exotic quarks than with top quark. In this case, the exotic quarks may
contribute more significantly than top quark in productions of the neutral
scalar Higgs bosons in the gluon fusion process. We find that there is indeed
some parameter region in the USSM that supports our speculations.Comment: 18 pages; changed content; JPhys
Double symmetry breaking and 2D quantum phase diagram in spin-boson systems
The quantum ground state properties of two independent chains of spins
(two-levels systems) interacting with the same bosonic field are theoretically
investigated. Each chain is coupled to a different quadrature of the field,
leading to two independent symmetry breakings for increasing values of the two
spin-boson interaction constants and . A phase diagram is
provided in the plane (,) with 4 different phases that can
be characterized by the complex bosonic coherence of the ground states and can
be manipulated via non-abelian Berry effects. In particular, when
and are both larger than two critical values, the fundamental
subspace has a four-fold degeneracy. Possible implementations in
superconducting or atomic systems are discussed
Quantum criticality in spin chains with non-ohmic dissipation
We investigate the critical behavior of a spin chain coupled to bosonic baths
characterized by a spectral density proportional to , with .
Varying changes the effective dimension of the
system, where is the dynamical critical exponent and the number of spatial
dimensions is set to one. We consider two extreme cases of clock models,
namely Ising-like and U(1)-symmetric ones, and find the critical exponents
using Monte Carlo methods. The dynamical critical exponent and the anomalous
scaling dimension are independent of the order parameter symmetry for
all values of . The dynamical critical exponent varies continuously from for to for , and the anomalous scaling dimension
evolves correspondingly from to . The latter
exponent values are readily understood from the effective dimensionality of the
system being for , while for the anomalous
dimension takes the well-known exact value for the 2D Ising and XY models,
since then . A noteworthy feature is, however, that
approaches unity and approaches 1/4 for values of , while naive
scaling would predict the dissipation to become irrelevant for . Instead,
we find that for for both Ising-like and U(1)
order parameter symmetry. These results lead us to conjecture that for all
site-dissipative chains, these two exponents are related by the scaling
relation . We also connect our results to
quantum criticality in nondissipative spin chains with long-range spatial
interactions.Comment: 8 pages, 6 figure
Hidden Caldeira-Leggett dissipation in a Bose-Fermi Kondo model
We show that the Bose-Fermi Kondo model (BFKM), which may find applicability
both to certain dissipative mesoscopic qubit devices and to heavy fermion
systems described by the Kondo lattice model, can be mapped exactly onto the
Caldeira-Leggett model. This mapping requires an ohmic bosonic bath and an
Ising-type coupling between the latter and the impurity spin. This allows us to
conclude unambiguously that there is an emergent Kosterlitz-Thouless quantum
phase transition in the BFKM with an ohmic bosonic bath. By applying a bosonic
numerical renormalization group approach, we thoroughly probe physical
quantities close to the quantum phase transition.Comment: Final version appearing in Physical Review Letter
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