A density matrix approach to the dynamical properties of a two-site Holstein model

The two-site Holstein model represents a first non-trivial paradigm for the interaction between an itinerant charge with a quantum oscillator, a very common topic in different ambits. Exact results can be achieved both analytically and numerically, nevertheless it can be useful to compare them with approximate, semi-classical techniques in order to highlight the role of quantum effects. In this paper we consider the adiabatic limit in which the oscillator is very much slow than the electron. A density matrix approach is introduced for studying the charge dynamics and the exact results are compared with two different approximations: a Born-Oppenheimer-based Static Approximation for the oscillator (SA) and a Quantum-classical (QC) dynamics

Current transport properties and phase diagram of a Kitaev chain with long-range pairing

We describe a method to probe the quantum phase transition between the short-range topological phase and the long-range topological phase in the superconducting Kitaev chain with long-range pairing, both exhibiting subgap modes localized at the edges. The method relies on the effects of the finite mass of the subgap edge modes in the long-range regime (which survives in the thermodynamic limit) on the single-particle scattering coefficients through the chain connected to two normal leads. Specifically, we show that, when the leads are biased at a voltage V with respect to the superconducting chain, the Fano factor is either zero (in the short-range correlated phase) or 2e (in the long-range correlated phase). As a result, we find that the Fano factor works as a directly measurable quantity to probe the quantum phase transition between the two phases. In addition, we note a remarkable "critical fractionalization effect" in the Fano factor, which is exactly equal to e along the quantum critical line. Finally, we note that a dual implementation of our proposed device makes it suitable as a generator of large-distance entangled two-particle states.Comment: 24 pages, 8 .eps figures Published versio

Conditional sign flip via teleportation

We present a model to realize a probabilistic conditional sign flip gate using only linear optics. The gate operates in the space of number state qubits and is obtained by a nonconventional use of the teleportation protocol. Both a destructive and a nondestructive version of the gate are presented. In the former case an Hadamard gate on the control qubit is combined with a projective teleportation scheme mixing control and target. The success probability is 1/2. In the latter case we need a quantum encoder realized via the interaction of the control qubit with an ancillary state composed of two maximally entangled photons. The success probability is 1/4

Bose-glass phases of ultracold atoms due to cavity backaction

We determine the quantum ground-state properties of ultracold bosonic atoms interacting with the mode of a high-finesse resonator. The atoms are confined by an external optical lattice, whose period is incommensurate with the cavity mode wave length, and are driven by a transverse laser, which is resonant with the cavity mode. While for pointlike atoms photon scattering into the cavity is suppressed, for sufficiently strong lasers quantum fluctuations can support the build-up of an intracavity field, which in turn amplifies quantum fluctuations. The dynamics is described by a Bose-Hubbard model where the coefficients due to the cavity field depend on the atomic density at all lattice sites. Quantum Monte Carlo simulations and mean-field calculations show that for large parameter regions cavity backaction forces the atoms into clusters with a checkerboard density distribution. Here, the ground state lacks superfluidity and possesses finite compressibility, typical of a Bose-glass. This system constitutes a novel setting where quantum fluctuations give rise to effects usually associated with disorder.Comment: 5 pages, 3 figures, new numerical simulations are adde

Observation of the Quantum Zeno Effect on a NISQ Device

We study the Quantum Zeno Effect (QZE) on a single qubit on IBM Quantum Experience devices under the effect of multiple measurements. We consider two possible cases: the Rabi evolution and the free decay. In both cases we observe the occurrence of the QZE as an increasing of the survival probability with the number of measurements

Routing quantum information in spin chains

Two different models for performing efficiently routing of a quantum state are presented. Both cases involve an XX spin chain working as data bus and additional spins that play the role of sender and receivers, one of which is selected to be the target of the quantum state transmission protocol via a coherent quantum coupling mechanism making use of local/global magnetic fields. Quantum routing is achieved, in the first of the models considered, by weakly coupling the sender and the receiver to the data bus. In the second model, strong magnetic fields acting on additional spins located between the sender/receiver and the data bus allow us to perform high fidelity routing.Comment: added references in v

Investigation on the feasibility of integration of high temperature solar energy in a textile factory

Thermal energy production from fossil fuels is very common in many applications, especially in industrial processes. In a global context where great attention is being focused on reducing pollution and greenhouse gas production, the integration of renewable energy in industrial applications is very interesting. This is even more important considering that greenhouse gas emission for industrial processes is a great portion of their total emission. Considering the above, it appears that the integration of high temperature solar panels in industrial processes is quite an attractive prospect. The working temperatures of parabolic solar collectors are, for example, generally close to those of the thermal fluids used in many industrial processes, and parabolic solar collectors are a well known technology with several applications primarily used in electric production systems. Nonetheless, only a few examples of industrial integration have been studied or built. In this study, the integration of a concentrating solar thermal plant in a textile factory has been examined both from the thermodynamic and economic point of view. An existing textile factory was chosen as a case study and its annual consumption of thermal energy characterized. A model of the plant with solar energy integration was developed and simulated with TRNSYS over a one year time period. The plant was simulated considering the panel characteristics provided by the manufacturer and the local irradiation data. The influence of several plant parameters has been investigated in order to estimate their importance on performance and plant suitability

Mutual information for fermionic systems

We study the behavior of the mutual information (MI) in various quadratic fermionic chains, with and without pairing terms and both with short- and long-range hoppings. The models considered include the short-range Kitaev model and also cases in which the area law for the entanglement entropy is - logarithmically or non-logarithmically - violated. When the area law is violated at most logarithmically, the MI is a monotonically increasing function of the conformal four-point ratio x, also for the Kitaev model. Where non-logarithmic violations of the area law are present, then non-monotonic features of MI can be observed, with a structure of peaks related to the spatial configuration of Bell pairs, and the four-point ratio x is found to be not sufficient to capture the whole structure of the MI. For the model exhibiting perfect volume law, the MI vanishes identically. For the Kitaev model, when it is gapped or the range of the pairing is large enough, then the results have vanishing MI for small x. A discussion of the comparison with the results obtained by the AdS/CFT correspondence in the strong coupling limit is presented