8 research outputs found
Griffiths phases in the strongly disordered Kondo necklace model
The effect of strong disorder on the one-dimensional Kondo necklace model is
studied using a perturbative real-space renormalization group approach which
becomes asymptotically exact in the low energy limit. The phase diagram of the
model presents a random quantum critical point separating two phases; the {\em
random singlet phase} of a quantum disordered XY chain and the random Kondo
phase. We also consider an anisotropic version of the model and show that it
maps on the strongly disordered transverse Ising model. The present results
provide a rigorous microscopic basis for non-Fermi liquid behavior in
disordered heavy fermions due to Griffiths phases.Comment: 4 pages, 4 figure
Phase diagram of the random Heisenberg antiferromagnetic spin-1 chain
We present a new perturbative real space renormalization group (RG) to study
random quantum spin chains and other one-dimensional disordered quantum
systems. The method overcomes problems of the original approach which fails for
quantum random chains with spins larger than S=1/2. Since it works even for
weak disorder we are able to obtain the zero temperature phase diagram of the
random antiferromagnetic Heisenberg spin-1 chain as a function of disorder. We
find a random singlet phase for strong disorder and as disorder decreases, the
system shows a crossover from a Griffiths to a disordered Haldane phase.Comment: 4 pages, 10 figure
Random Spin-1 Quantum Chains
We study disordered spin-1 quantum chains with random exchange and
biquadratic interactions using a real space renormalization group approach. We
find that the dimerized phase of the pure biquadratic model is unstable and
gives rise to a random singlet phase in the presence of weak disorder. In the
Haldane region of the phase diagram we obtain a quite different behavior.Comment: 13 pages, Latex, no figures, to be published in Solid State
Communication
Localization effects in disordered quantum batteries
We investigate the effect of localization on the local charging of quantum
batteries (QBs) modeled by disordered spin systems. Two distinct schemes based
on the transverse-field random Ising model are considered, with Ising couplings
defined on a Chimera graph and on a linear chain with up to next-to-nearest
neighbor interactions. By adopting a low-energy demanding charging process
driven by local fields only, we obtain that the maximum extractable energy by
unitary processes (ergotropy) is highly enhanced in the ergodic phase in
comparison with the many-body localization (MBL) scenario. As we turn off the
next-to-nearest neighbor interactions in the Ising chain, we have the onset of
the Anderson localization phase. We then show that the Anderson phase exhibits
a hybrid behavior, interpolating between large and small ergotropy as the
disorder strength is increased. We also consider the splitting of total
ergotropy into its coherent and incoherent contributions. This incoherent part
implies in a residual ergotropy that is fully robust against dephasing, which
is a typical process leading to the self-discharging of the battery in a real
setup. Our results are experimentally feasible in scalable systems, such as in
superconducting integrated circuits.Comment: 8 pages and 7 figures. Comments are welcome
Charging power and stability of always-on transitionless driven quantum batteries
The storage and transfer of energy through quantum batteries are key elements in quantum networks. Here, we propose a charger design based on transitionless quantum driving (TQD), which allows for inherent control over the battery charging time, with the speed of charging coming at the cost of the internal energy available to implement the dynamics. Moreover, the TQD-based charger is also shown to be locally stable, which means that the charger can be disconnected from the quantum battery (QB) at any time after the energy transfer to the QB, with no full energy backflow to the charger. This provides a highly charged QB in an always-on asymptotic regime. We illustrate the robustness of the QB charge against time fluctuations and the full control over the evolution time for a feasible TQD-based charger