arXiv subjects

Benedetto Militello

Publications and source records attributed to Benedetto Militello.

At least 19 recordsLinked to original sources

arXiv2025

Short-time behavior of a system ruled by non-Hermitian time-dependent Hamiltonians

The short-time behavior of the survival probability of a system governed by a time-dependent non-Hermitian Hamiltonian is derived using to the second order perturbative approach. The resulting expression allows for the analysis of some situations which could be of interest in the field of quantum technology. For example, it becomes possible to predict a quantum Zeno effect even in the presence of decay processes.

quant-ph↗

arXiv2024

Generalized Cluster Correlation Expansion theory for STIRAP processes in the presence of a spin bath

The Stimulated Raman Adiabatic Passage (STIRAP) is applied to a system coupled to a bath made of fully-interacting two-level systems, whose dynamics is studied exploiting the generalized Cluster Correlation Expansion (gCCE) theory. We specialize our analysis to a negatively charged silicon vacancy (SiV-1) in non-purified 4H-SiC to assess the possibility of transferring population between two states of the ground manifold, also taking into account the interaction with a spherical nuclear spin bath formed by nuclei of 29Si and 13C. For this system, it is demonstrated that the presence of a small/medium sized bath has no effect on the protocol, finding in particular a set of parameter values for an efficient STIRAP process.

cond-mat.mes-hall↗

arXiv2024

Adiabatically-manipulated systems interacting with spin baths beyond the Rotating Wave Approximation

The Stimulated Raman Adiabatic Passage on a three-state system interacting with a spin bath is considered focusing on the efficiency of the population transfer. Our analysis is based on the perturbation treatment of the interaction term evaluated beyond the Rotating Wave Approximation, thus focusing on the limit of weak system-bath coupling. The analytical expression of the correction to the efficiency and consequent numerical analysis show that in most of the cases the effects of the environment are negligible, confirming the robustness of the population transfer.

quant-ph↗

arXiv2023

Adiabatic manipulation of a system interacting with a spin-bath

Stimulated Raman Adiabatic Passage, a very efficient technique for manipulating a quantum system based on the adiabatic theorem, is analyzed in the case where the manipulated physical system is interacting with a spin bath. Exploitation of the rotating wave approximation allows for the identification of a constant of motion which simplifies both the analytical and the numerical treatment, which allows for evaluating the total unitary evolution of system and bath. The efficiency of the population transfer process is investigated in several regimes, including the weak and strong coupling with the environment and the off-resonance. The formation of appropriate Zeno subspaces explains the lowering of the efficiency in the strong damping regime.

quant-ph↗

arXiv2023

Generation of minimum energy entangled states

Quantum technologies exploiting bipartite entanglement could be made more efficient by using states having the minimum amount of energy for a given entanglement degree. Here, we study how to generate these states in the case of a bipartite system of arbitrary finite dimension either by applying a unitary transformation to its ground state or through a zero-temperature thermalization protocol based on turning on and off a suitable interaction term between the subsystems. In particular, we explicitly identify three possible unitary operators and five possible interaction terms. On one hand, two of the three unitary transformations turn out to be easily decomposable in terms of local elementary operations and a single nonlocal one, making their implementation easier. On the other hand, since the thermalization procedures can be easily adapted to generate many different states, we numerically show that, for each degree of entanglement, generating minimum-energy entangled states costs, in general, less than generating the vast majority of the other states.

quant-ph↗

arXiv2023

Simple scheme for extracting work with a single bath

We propose a simple protocol exploiting the thermalization of a $\textit{storage}$ bipartite system $S$ to extract work from a $\textit{resource}$ system $R$. The protocol is based on a recent work definition involving only a single bath. A general description of the protocol is provided without specifying the characteristics of $S$. We quantify both the extracted work and the ideal efficiency of the process also giving maximum bounds for them. Then, we apply the protocol to two cases: two interacting qubits and the Rabi model. In both cases, for very strong couplings, an extraction of work comparable with the bare energies of the subsystems of $S$ is obtained and its peak is reached for finite values of the bath temperature, $T$. We finally show, in the Rabi model at $T=0$, how to transfer the work stored in $S$ to an external device, permitting thus a cyclic implementation of the whole work-extraction protocol. Our proposal makes use of simple operations not needing fine control.

quant-ph↗

arXiv2023

Energy bounds for entangled states

We find the minimum and the maximum value for the local energy of an arbitrary finite bipartite system for any given amount of entanglement, also identifying families of states reaching these bounds and sharing formal analogies with thermal states. Then, we numerically study the probability of randomly generating pure states close to these energy bounds finding, in all the considered configurations, that it is extremely low except for the two-qubit and highly degenerate cases. These results can be important in quantum technologies to design energetically more efficient protocols.

quant-ph↗

arXiv2023

Extraction of Work via a Thermalization Protocol

This extended abstract contains an outline of the work reported at the conference IQIS2018. We show that it is possible to exploit a thermalization process to extract work from a resource system $R$ to a bipartite system $S$. To do this, we propose a simple protocol in a general setting in the presence of a single bath at temperature $T$ and then examine it when $S$ is described by the quantum Rabi model at $T=0$. We find the theoretical bounds of the protocol in the general case and we show that when applied to the Rabi model it gives rise to a satisfactory extraction of work and efficiency.

quant-ph↗

arXiv2022

Quantum correlations beyond entanglement in a classical-channel model of gravity

A direct quantization of the Newtonian interaction between two masses is known to establish entanglement, which if detected would witness the quantum nature of the gravitational field. Gravitational interaction is yet compatible also with gravitational decoherence models relying on classical channels, hence unable to create entanglement. Here, we show in paradigmatic cases that, despite the absence of entanglement, a classical-channel model of gravity can still establish quantum correlations in the form of quantum discord between two masses. This is demonstrated for the Kafri-Taylor-Milburn (KTM) model and a recently proposed dissipative extension of this. In both cases, starting from an uncorrelated state, a significant amount of discord is generally created. This eventually decays in the KTM model, while it converges to a small stationary value in its dissipative extension. We also find that initial local squeezing on the state of the masses can significanlty enhance the generated discord.

quant-ph↗

arXiv2021

Quantum synchronisation and clustering in chiral networks

We study the emergence of synchronisation in a chiral network of harmonic oscillators. The network consists of a set of locally incoherently pumped harmonic oscillators coupled pairwise in cascade with travelling field modes. Such cascaded coupling leads to feedback-less dissipative interaction between the harmonic oscillators of the pair which can be described in terms of an effective pairwise hamiltonian a collective pairwise decay. The network is described mathematically in terms of a directed graph. By analysing geometries of increasing complexity we show how the onset of synchronisation depends strongly on the network topology, with the emergence of synchronised communities in the case of complex networks. The quantum nature of the non local correlation between network nodes is assessed.

quant-ph↗

arXiv2021

Evanescent Wave Approximation for Non-Hermitian Hamiltonians

The counterpart of the rotating wave approximation for non-Hermitian Hamiltonians is considered, which allows for the derivation of a suitable effective Hamiltonian for systems with some states undergoing decays. In the limit of very high decay rates, on the basis of this effective description we can predict the occurrence of a quantum Zeno dynamics which is interpreted as the removal of some coupling terms and the vanishing of an operatorial pseudo-Lamb shift.

quant-ph↗

arXiv2020

Open multistate Majorana model

The multistate Majorana model in the presence of dissipation and dephasing is considered. It is proven that increasing the Hilbert space dimension the system becomes more and more fragile to quantum noise. The impossibility to recast the problem in the form of a set of independent spin-$1/2$ problems because of the presence of the noise is pointed out.

quant-ph↗

arXiv2020

Hilbert space partitioning for non-Hermitian Hamiltonians: From off-resonance to Zeno subspaces

Effective non-Hermitian Hamiltonians describing decaying systems are derived and analyzed in connection with the occurrence of possible Hilbert space partitioning, resulting in a confinement of the dynamics. In some cases, this fact can be interpreted properly as Zeno effect or Zeno dynamics, according to the dimension of the subspace one focuses on; in some other cases, the interpretation is more complicated and traceable back to a mix of Zeno phenomena and lack of resonance. Depending on the complex phases of the diagonal terms of the Hamiltonian, the system reacts in different ways, requiring larger moduli for the dynamical confinement to occur when the complex phase is close to $π/2$.

quant-ph↗

arXiv2019

Master equation approach to the three-state open Majorana model

The three-state Majorana model in the presence of dissipation is considered. Different models of system-environment interaction are explored, ranging from situation where dissipation is the main effect to regimes where dephasing is mainly produced. It is shown that the detrimental effects of the noise are stronger in the presence of dissipation than in the presence of dephasing. The role of temperature is also discussed.

quant-ph↗

arXiv2019

Degenerate Landau-Zener model in the presence of quantum noise

The degenerate Landau-Zener-Majorana-Stückelberg model consists of two degenerate energy levels whose energies vary with time and in the presence of an interaction which couples the states of the two levels. In the adiabatic limit, it allows for the populations transfer from states of one level to states of the other level. The presence of an interaction with the environment influences the efficiency of the process. Nevertheless, identification of possible decoherence-free subspaces permits to engineer coupling schemes for which quantum noise can be minimized.

quant-ph↗

arXiv2019

Three-state Landau-Zener model in the presence of dissipation

A population transfer based on adiabatic evolutions in a three-state system undergoing an avoided crossing is considered. The efficiency of the process is analyzed in connection with the relevant parameters, bringing to light an important role of the phases of the coupling constants. The role of dissipation is also taken into account, focusing on external decays that can be described by effective non-Hermitian Hamiltonians. Though the population transfer turns out to be quite sensitive to the decay processes, for very large decay rates the occurrence of a Zeno-phenomenon allows for restoring a very high efficiency.

quant-ph↗

arXiv2018

Steepest Entropy Ascent for Two-State Systems with Slowly Varying Hamiltonians

The Steepest Entropy Ascent approach is considered and applied to few-state systems. When the Hamiltonian of the system is time dependent, the principle of maximum entropy production can still be exploited; arguments to support this fact are given. In the limit of slowly varying Hamiltonians which allows for the adiabatic approximation for the unitary part of the dynamics, the system exhibits significant robustness to the thermalization process. Specific examples such as a spin in a rotating field and a generic two-state system undergoing an avoided crossing are considered.

quant-ph↗

arXiv2017

Competition of Direct and Indirect Sources of Thermal Entanglement in a spin star network

A spin star system consisting of three peripheral two-state systems and a central one is considered, with the peripheral spins assumed to interact with each other, as well as with the central one. It is shown that such two couplings, each one being a thermal entanglement source, can significantly compete in the formation of quantum correlations in the thermal state, to the point that they can destroy any thermal entanglement of the peripheral spins.

quant-ph↗