Manipulation of the dynamics of many-body systems via quantum control methods

We investigate how dynamical decoupling methods may be used to manipulate the time evolution of quantum many-body systems. These methods consist of sequences of external control operations designed to induce a desired dynamics. The systems considered for the analysis are one-dimensional spin-1/2 models, which, according to the parameters of the Hamiltonian, may be in the integrable or non-integrable limits, and in the gapped or gapless phases. We show that an appropriate control sequence may lead a chaotic chain to evolve as an integrable chain and a system in the gapless phase to behave as a system in the gapped phase. A key ingredient for the control schemes developed here is the possibility to use, in the same sequence, different time intervals between control operations.Comment: 10 pages, 3 figure

Delocalization and wave-packet dynamics in one-dimensional diluted Anderson models

We study the nature of one-electron eigen-states in a one-dimensional diluted Anderson model where every Anderson impurity is diluted by a periodic function $f(l)$ . Using renormalization group and transfer matrix techniques, we provide accurate estimates of the extended states which appear in this model, whose number depends on the symmetry of the diluting function $f(l)$. The density of states (DOS) for this model is also numerically obtained and its main features are related to the symmetries of the diluting function $f(l)$. Further, we show that the emergence of extended states promotes a sub-diffusive spread of an initially localized wave-packet.Comment: 6 pages, 6 figures, to appear in EPJ

Updating constraints on phantom crossing f(T)f(T) gravity

We establish constraints on $f(T)$ gravity by considering the possibility of a scenario that supports a phantom crossing of the equation of state parameter $\omega_{DE}$. After determining the viable parameter space of the model, while checking the impact on the background dynamics, we perform an analysis to obtain constraints on cosmological parameters and determine the viability of this scenario. To this end, we use combined data sets from cosmic chronometers (CC), baryonic acoustic oscillations (BAO), redshift space distortion (RSD) and Type Ia supernovae (SN) measurements from the latest Pantheon$+$ set, in which the impact on the absolute magnitude due to the change of the effective gravitational constant is also considered. It is found that a state where a phantom crossing of $\omega_{DE}$ happens is favored by data, and the $f(T)$ model is competitive with the $\Lambda$CDM one by statistical criteria, such as AIC and BIC. Additionally, we find evidence of the Hubble tension being alleviated within the $f(T)$ model, at the same time that it does not worsen the growth one, indicating a possibility of the present scenario as an option to address the current cosmic tensions.Comment: 18 pages, 6 figures, 2 tables. Updated results and references; published in JCA

Many-particle confinement by constructed disorder and quantum computing

Many-particle confinement (localization) is studied for a 1D system of spinless fermions with nearest-neighbor hopping and interaction, or equivalently, for an anisotropic Heisenberg spin-1/2 chain. This system is frequently used to model quantum computers with perpetually coupled qubits. We construct a bounded sequence of site energies that leads to strong single-particle confinement of all states on individual sites. We show that this sequence also leads to a confinement of all many-particle states in an infinite system for a time that scales as a high power of the reciprocal hopping integral. The confinement is achieved for strong interaction between the particles while keeping the overall bandwidth of site energies comparatively small. The results show viability of quantum computing with time-independent qubit coupling.Comment: An invited paper for the topical issue of J. Opt. B on quantum contro