arXiv subjects

David Edward Bruschi

Publications and source records attributed to David Edward Bruschi.

At least 19 recordsLinked to original sources

arXiv2026

Gravitational redshift as a quantum channel: modeling the effects of gravitational redshift in quantum optics

The gravitational frequency shift of light is well understood in the theory of classical electromagnetism. Nevertheless, its description in quantum theory is not yet fully developed. Recent work pointed out inconsistencies in previously developed models aimed at describing the gravitational redshift as an effective multi-mode mixer (MMM) acting on modes of light, but so far a complete solution of these issues was not obtained. Here, we identify the root cause of the MMM model's inconsistency and provide two complementary approaches to correct it: a "natural" one from a field-theoretic perspective, and another adapted to the language of quantum mechanics of finite-dimensional systems. We show that the second approach allows for modeling of the redshift in a multi-mode transmission setup as a quantum channel that can be characterized using standard quantum information-theoretic techniques when restricting the input states to Gaussian states of light.

quant-ph↗

arXiv2026

Self gravity decoheres quantum systems

We study the effects of self gravity on the quantum state of a massive and static particle that initially contains quantum coherence between two positions. We employ linearized quantum gravity to obtain the self-interacting dynamics of the particle mediated by gravitons, and find that the effective evolution of the particle's state can be viewed as a quantum channel composed of a unitary, dephasing, depolarizing, and erasure part. Depolarization drives the state towards maximal mixedness while depolarization and dephasing decrease its quantum coherence. Crucially, the intrinsic diffusion and dephasing timescales of the problem determine a relation between the mass and size of the particle that naturally identifies the transition between its classical and quantum regime. Our work therefore provides an explanation for the observational difference between the quantum behavior of small and light systems and the classical behavior of larger and heavier ones.

quant-ph↗

arXiv2026

High-order interactions in quantum optomechanics: fluctuations, dynamics and thermodynamics

Quantum optomechanics describes the interaction between a confined field and a fluctuating wall due to radiation pressure. The dynamics of this system is typically understood using perturbation theory up to second order in the small coupling. Improving beyond this regime can shed light onto new phenomena. In this work we study high-order resonant wall-field interactions characterized by two- and three-phonon scattering processes. We obtain the Hamiltonian, compute the perturbed energy spectrum and explicitly calculate corrections to the ground state. Finally, we study the dynamics of the system when second- and third-order resonance conditions are activated, showing that the presence of high-order terms in the Hamiltonian drastically affects the populations of all particles, as well as the entropy production rate.

quant-ph↗

arXiv2026

Limits to the validity of gravitational redshift as a quantum-optical multimode mixer

We analyze the domain of validity of a quantum optical model that describes the effects of gravitational redshift on the quantum state of photons that propagate in curved spacetime. This model assumes that the modes defining the initial state of the photon are mixed with an auxiliary environment mode via an effective multimode mixer. We find that the model, as proposed, is consistent only to first order for small redshift, where the range of validity is conditional not only to the gravitational parameters, but also to those that define the photonic modes. We identify the problem and provide a partial solution in terms of a necessary condition on the transformation matrix representing the process, which requires the use of a number of auxiliary modes that is at least equal to the number of modes that define the photonic state. We conclude by discussing implications for theoretical quantum optics and photonics in curved spacetime, as well as for the development of quantum technologies.

quant-ph↗

arXiv2026

Gravitational redshift of broadband relativistic quantum photons

We employ linearized quantum gravity to study gravitational redshift of photons in the context of relativistic and quantum physics, where photons interact in flat spacetime with a classical massive body via graviton exchange. We find that gravitational redshift, as predicted by general relativity, occurs only in the case of localized photons with a well defined momentum that interact with a classical source of gravitons. On the contrary, photons initially prepared in states with nonclassical features, such as quantum coherence in the position degree of freedom, witness no well-defined redshift in general. Our work not only shows that gravitational redshift can be found in flat spacetime as a consequence of the interaction of quantum fields, but it also challenges the robustness of one of the most important predictions of general relativity, furthermore indicating that deviations from the theory can already be observed at low energies using highly nonclassical photonic states.

gr-qc↗

arXiv2026

On the structural properties of Lie algebras via associated labeled directed graphs

We present a method for associating labeled directed graphs to finite-dimensional Lie algebras, thereby enabling rapid identification of key structural algebraic features. To formalize this approach, we introduce the concept of graph-admissible Lie algebras and analyze properties of valid graphs given the antisymmetry property of the Lie bracket as well as the Jacobi identity. Based on these foundations, we develop graph-theoretic criteria for solvability, nilpotency, presence of ideals, simplicity, semisimplicity, and reductiveness of an algebra. Practical algorithms are provided for constructing such graphs and those associated with the lower central series and derived series via an iterative pruning procedure. This visual framework allows for an intuitive understanding of Lie algebraic structures that goes beyond purely visual advantages, since it enables a simpler and swifter grasping of the algebras of interest beyond computational-heavy approaches. Examples, which include the Schrödinger and Lorentz algebra, illustrate the applicability of these tools to physically relevant cases. We further explore applications in physics, where the method facilitates computation of similtude relations essential for determining quantum mechanical time evolution via the Lie algebraic factorization method. Extensions to graded Lie algebras and related conjectures are discussed. Our approach bridges algebraic and combinatorial perspectives, offering both theoretical insights and computational tools into this area of mathematical physics.

math-ph↗

arXiv2025

Finite-dimensional Lie algebras in bosonic quantum dynamics: The single-mode case

We study, classify, and explore the mathematical properties of finite-dimensional Lie algebras occurring in the quantum dynamics of single-mode and self-interacting bosonic systems. These Lie algebras are contained in the real skew-hermitian Weyl algebra $\hat{A}_1$, defined as the real subalgebra of the Weyl algebra $A_1$ consisting of all skew-hermitian polynomials. A central aspect of our analysis is the choice of basis for $\hat{A}_1$, which is composed of skew-symmetric combinations of two elements of the Weyl algebra called monomials, namely strings of creation and annihilation operators combined with their hermitian conjugate. Motivated by the quest for analytical solutions in quantum optimal control and dynamics, we aim at answering the following three fundamental questions: (i) What are the finite-dimensional Lie subalgebras in $\hat{A}_1$ generated by monomials alone? (ii)~What are the finite-dimensional Lie subalgebras in $\hat{A}_1$ that contain the free Hamiltonian? (iii) What are the non-abelian and finite-dimensional Lie subalgebras that can be faithfully realized in $\hat{A}_1$? We answer the first question by providing all possible realizations of all finite-dimensional non-abelian Lie algebras that are generated by monomials alone. We answer the second question by proving that any non-abelian and finite-dimensional subalgebra of $\hat{A}_1$ that contains a free Hamiltonian term must be a subalgebra of the Schrödinger algebra. We partially answer the third question by classifying all nilpotent and non-solvable Lie algebras that can be realized in $\hat{A}_1$, and comment on the remaining cases. Finally, we also discuss the implications of our results for quantum control theory. Our work constitutes an important stepping stone to understanding quantum dynamics of bosonic systems in full generality.

quant-ph↗

arXiv2025

Bounding the rotating wave approximation for coupled harmonic oscillators

In this work we study the validity of the rotating wave approximation of an ideal system composed of two harmonic oscillators evolving with a quadratic Hamiltonian and arbitrarily strong interaction. We prove its validity for arbitrary states by bounding the error introduced. We then restrict ourselves to the dynamics of Gaussian states and are able to fully quantify the deviation of arbitrary pure Gaussian states that evolve through different dynamics from a common quantum state. We show that this distance is fully determined by the first and second moments of the statistical distribution of the number of excitations created from the vacuum during an appropriate effective time-evolution. We use these results to completely control the dynamics for this class of states, therefore providing a toolbox to be used in quantum optics and quantum information. Applications and potential physical implementations are also discussed.

quant-ph↗

arXiv2024

Quantum heat engine based on quantum interferometry: the SU(1,1) Otto cycle

We present a quantum heat engine based on a quantum Otto cycle, whose working substance reproduces the same outcomes of a SU(1,1) interference process at the end of each adiabatic transformation. This device takes advantage of the extraordinary quantum metrological features of the SU(1,1) interferometer to better discriminate the sources of uncertainty of relevant observables during each adiabatic stroke of the cycle. Applications to circuit QED platforms are also discussed.

quant-ph↗

arXiv2024

Particle creation in left-handed metamaterial transmission lines

Transmission lines are excellent examples of quantum simulators of quantum fields. By appropriately driving specific circuit elements, these devices can reproduce relativistic and quantum such as particle creation due to the non-adiabatic stimulation of the quantum vacuum. We investigate particle creation in left-handed transmission lines induced by the modulation of the Josephson energy in superconducting quantum interference devices. Our results show that, as a consequence of the peculiar dispersion relations present in these systems, particle production occurs with much more favorable conditions with respect to the usual right-handed transmission lines.

quant-ph↗

arXiv2024

Deciding finiteness of bosonic dynamics with tunable interactions

In this work we are motivated by factorization of bosonic quantum dynamics and we study the corresponding Lie algebras, which can potentially be infinite dimensional. To characterize such factorization, we identify conditions for these Lie algebras to be finite dimensional. We consider cases where each free Hamiltonian term is itself an element of the generated Lie algebra. In our approach, we develop new tools to systematically divide skew-hermitian bosonic operators into appropriate subspaces, and construct specific sequences of skew-hermitian operators that are used to gauge the dimensionality of the Lie algebras themselves. The significance of our result relies on conditions that constrain only the independently controlled generators in a particular Hamiltonian, thereby providing an effective algorithm for verifying the finiteness of the generated Lie algebra. In addition, our results are tightly connected to mathematical work where the polynomials of creation and annihilation operators are known as the Weyl algebra. Our work paves the way for better understanding factorization of bosonic dynamics relevant to quantum control and quantum technology.

quant-ph↗

arXiv2023

Phonon-photon conversion as mechanism for cooling and coherence transfer

The dynamical Casimir effect is the physical phenomenon where the mechanical energy of a movable wall of a cavity confining a quantum field can be converted into quanta of the field itself. This effect has been recognized as one of the most astonishing predictions of quantum field theory. At the quantum scale, the energy conversion can also occur incoherently, namely without an physical motion of the wall. We employ quantum thermodynamics to show that this phenomenon can be employed as a tool to cool down the wall when there is a non-vanishing temperature gradient between the wall and the cavity. At the same time, the process of heat-transfer enables to share the coherence from one cavity mode, driven by a laser, to the wall, thereby forcing its coherent oscillation. Finally, we show how to employ one laser drive to cool the entire system including the case when it is composed of other subsystems.

quant-ph↗

arXiv2023

Relativistic quantum communication between harmonic oscillator detectors

We propose a model of communication employing two harmonic oscillator detectors interacting through a scalar field in a background Minkowski spacetime. In this way, the scalar field plays the role of a quantum channel, namely a Bosonic Gaussian channel. The classical and quantum capacities of the communication channel are found, assuming that the detectors' spatial dimensions are negligible compared to their distance. In particular, we study the evolution in time of the classical capacity after the detectors-field interaction is switched on for various detectors' frequencies and coupling strengths with the field. As a result, we find a finite value of these parameters optimizing the communication of classical messages. Instead, a reliable communication of quantum messages turns out to be always inhibited.

gr-qc↗

arXiv2023

Gravity-induced electric currents

We study the generation of an electric current in an ideal conducting coil, immersed in a magnetic field, due to the occurrence of a gravitational perturbation. We show that this effect can be used to detect gravitational waves impinging on the coil as well as gravitational gradients when the coil moves in a static background gravitational field. Our work opens the way to employing induced electric signals to detect dynamical gravitational fields and for gradiometry.

gr-qc↗

arXiv2023

Introduction to gravitational redshift of quantum photons propagating in curved spacetime

Gravitational redshift is discussed in the context of quantum photons propagating in curved spacetime. A brief introduction to modelling realistic photons is first presented and the effect of gravity on the spectrum computed for photons largely confined along the direction of propagation. It is then shown that redshift-induced transformations on photon operators with sharp momenta are not unitary, while a unitary transformation can be constructed for realistic photons with finite bandwidth. The unitary transformation obtained is then characterized as a multimode mixing operation, which is a generalized rotation of the Hilbert-space basis. Finally, applications of these results are discussed with focus on performance of quantum communication protocols, exploitation of the effects for quantum metrology and sensing, as well as potential for tests of fundamental science.

quant-ph↗

arXiv2023

Quantum field heat engine powered by phonon-photon interactions

We present a quantum heat engine based on a cavity with two oscillating mirrors that confine a quantum field as the working substance. The engine performs an Otto cycle during which the walls and a field mode interact via a nonlinear Hamiltonian. Resonances between the frequencies of the cavity mode and the walls allow to transfer heat from the hot and the cold bath by exploiting the conversion between phononic and photonic excitations. We study the time evolution of the system and show that net work can be extracted after a full cycle. We evaluate the efficiency of the process.

quant-ph↗

arXiv2023

Quantum memories for fundamental science in space

Investigating and verifying the connections between the foundations of quantum mechanics and general relativity will require extremely sensitive quantum experiments. To provide ultimate insight into this fascinating area of physics, the realization of dedicated experiments in space will sooner or later become a necessity. Quantum technologies, and among them quantum memories in particular, are providing novel approaches to reach conclusive experimental results due to their advanced state of development backed by decades of progress. Storing quantum states for prolonged time will make it possible to study Bell tests on astronomical baselines, to increase measurement precision for investigations of gravitational effects on quantum systems, or enable distributed networks of quantum sensors and clocks. We here promote the case of exploiting quantum memories for fundamental physics in space, and discuss both distinct experiments as well as potential quantum memory platforms and their performance.

quant-ph↗

arXiv2022

Gravitational redshift induces quantum interference

We use quantum field theory in curved spacetime to show that gravitational redshift induces a unitary transformation on the quantum state of propagating photons. This occurs for realistic photons characterized by a finite bandwidth, while ideal photons with sharp frequencies do not transform unitarily. We find that the transformation is a mode-mixing operation, and we devise a protocol that exploits gravity to induce a Hong-Ou-Mandel-like interference effect on the state of two photons. Testing the results of this work can provide a demonstration of quantum field theory in curved spacetime.

quant-ph↗