arXiv subjects

Giovanni Francesco Diotallevi

Publications and source records attributed to Giovanni Francesco Diotallevi.

5 recordsLinked to original sources

arXiv2026

Closed-Form Generators for Perturbative Transformations in Static and Periodically Driven Quantum Systems

We introduce a unified framework for the practical implementation of perturbative transformations that overcomes the limitations of existing construction methods. The central result is a closed-form operator expression for the generator of a broad class of perturbative transformations in systems composed of finite-dimensional and bosonic subspaces. We further generalize the construction to time-dependent systems with periodic perturbations, obtaining a solution that remains valid across low-, intermediate-, and high-frequency regimes, provided that the transition channels eliminated by the transformation remain sufficiently detuned. The derived framework remains independent of the particular perturbative scheme and therefore applies to a large class of perturbative approaches for both time independent and time dependent transformations. We demonstrate the scope and accuracy of the method by deriving effective dispersive interactions in exemplary anharmonic and periodically driven light--matter systems.

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arXiv2025

Maximal steady-state entanglement in autonomous quantum thermal machines

We devise an autonomous quantum thermal machine consisting of three pairwise-interacting qubits, two of which are locally coupled to thermal reservoirs. The machine operates autonomously, as it requires no time-coherent control, external driving or quantum bath engineering, and is instead propelled by a chemical potential bias. Under ideal conditions, we show that this out-of-equilibrium system can deterministically generate a maximally entangled steady-state between two of the qubits, or any desired pure two-qubit entangled state, emerging as a dark state of the system. We study the robustness of entanglement production with respect to several relevant parameters, obtaining nearly-maximally-entangled states well-away from the ideal regime of operation. Furthermore, we show that our machine architecture can be generalised to a configuration with $2n-1$ qubits, in which only a potential bias and two-body interactions are sufficient to generate genuine multipartite maximally entangled steady states in the form of a W state of $n$ qubits.

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arXiv2024

SymPT: a comprehensive tool for automating effective Hamiltonian derivations

The Schrieffer-Wolff transformation (SWT) is a foundational perturbative method for deriving effective Hamiltonians in quantum systems by systematically eliminating couplings between pairs of energy distant subspaces. Despite recent advancements, the implementation of SWTs for sufficiently complex systems remains computationally challenging and often requires extensive calculations that are prone to errors. In this work, we introduce an analytical software tool, SymPT (Symbolic Perturbation Theory), designed to automate the SWT and its extensions. Building on a universal framework developed in recent research, SymPT provides a systematic and generalizable solution for deriving the generator of the transformation, enabling accurate computation of effective Hamiltonians for arbitrary perturbative systems. The tool supports both time-independent and time-periodic Hamiltonians, extending beyond standard SWT to incorporate arbitrary coupling elimination, block-diagonalization and full-diagonalization routines, thus enabling precise handling of systems with intricate energy structures.

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arXiv2024

Fundamental limits on anomalous energy flows in correlated quantum systems

In classical thermodynamics energy always flows from the hotter system to the colder one. However, if these systems are initially correlated, the energy flow can reverse, making the cold system colder and the hot system hotter. This intriguing phenomenon is called ``anomalous energy flow'' and shows the importance of initial correlations in determining physical properties of thermodynamic systems. Here we investigate the fundamental limits of this effect. Specifically, we find the optimal amount of energy that can be transferred between quantum systems under closed and reversible dynamics, which then allows us to characterize the anomalous energy flow. We then explore a more general scenario where the energy flow is mediated by an ancillary quantum system that acts as a catalyst. We show that this approach allows for exploiting previously inaccessible types of correlations, ultimately resulting in an energy transfer that surpasses our fundamental bound. To demonstrate these findings, we use a well-studied quantum optics setup involving two atoms coupled to an optical cavity.

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arXiv2023

Steady-state entanglement production in a quantum thermal machine with continuous feedback control

Quantum thermal machines can generate steady-state entanglement by harvesting spontaneous interactions with local environments. However, using minimal resources and control, the entanglement is typically very noisy. Here, we study entanglement generation in a two-qubit quantum thermal machine in the presence of a continuous feedback protocol. Each qubit is measured continuously and the outcomes are used for real-time feedback to control the local system-environment interactions. We show that there exists an ideal operation regime where the quality of entanglement is significantly improved, to the extent that it can violate standard Bell inequalities and uphold quantum teleportation. In particular, we find, for ideal operation, that the heat current across the system is proportional to the entanglement concurrence. Finally, we investigate the robustness of entanglement production when the machine operates away from the ideal conditions.

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