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We introduce a new set of quantum channels: resonant multilevel amplitude damping (ReMAD) channels. Among other instances, they can describe energy dissipation effects in multilevel atomic systems induced by the interaction with a zero-temperature bosonic environment. At variance with the already known class of multilevel amplitude damping (MAD) channels, this new class of maps allows the presence of an environment unable to discriminate transitions with identical energy gaps. After characterizing the algebra of their composition rules, by analyzing the qutrit case, we show that this new set of channels can exhibit degradability and antidegradability in vast regions of the allowed parameter space. There we compute their quantum capacity and private classical capacity. We show that these capacities can be computed exactly also in regions of the parameter space where the channels aren't degradable nor antidegradable.

Advances in quantum technologies are giving rise to a revolution in the way fundamental physics questions are explored at the empirical level. At the same time, they are the seeds for future disruptive technological applications of quantum physics. Remarkably, a space-based environment may open many new avenues for exploring and employing quantum physics and technologies. Recently, space missions employing quantum technologies for fundamental or applied studies have been proposed and implemented with stunning results. The combination of quantum physics and its space application is the focus of this review: we cover both the fundamental scientific questions that can be tackled with quantum technologies in space and the possible implementation of these technologies for a variety of academic and commercial purposes., peer-reviewed

Recently, it was shown that when reference frames are associated to quantum systems, the transformation laws between such quantum reference frames need to be modified to take into account the quantum and dynamical features of the reference frames. This led to a relational description of the phase space variables of the quantum system of which the quantum reference frames are part of. While such transformations were shown to be symmetries of the system's Hamiltonian, the question remained unanswered as to whether they enjoy a group structure, similar to that of the Galilei group relating classical reference frames in quantum mechanics. In this work, we identify the canonical transformations on the phase space of the quantum systems comprising the quantum reference frames, and show that these transformations close a group structure defined by a Lie algebra, which is different from the usual Galilei algebra of quantum mechanics. We further find that the elements of this new algebra are in fact the building blocks of the quantum reference frames transformations previously identified, which we recover. Finally, we show how the transformations between classical reference frames described by the standard Galilei group symmetries can be obtained from the group of transformations between quantum reference frames by taking the zero limit of the parameter that governs the additional noncommutativity introduced by the quantum nature of inertial transformations., Comment: Version accepted in Quantum. 15 pages main text; 3 pages Appendix; 1 table

Introducing some fundamental concepts of quantum physics to high school students, and to their teachers, is a timely challenge. In this paper we describe ongoing research, in which a teaching–learning sequence for teaching quantum physics, whose inspiration comes from some of the fundamental papers about the quantum theory of radiation by Albert Einstein, is being developed. The reason for this choice goes back essentially to the fact that the roots of many subtle physical concepts, namely quanta, wave–particle duality and probability, were introduced for the first time in one of these papers, hence their study may represent a useful intermediate step towards tackling the final incarnation of these concepts in the full theory of quantum mechanics. An extended discussion of some elementary tools of statistical physics, mainly Boltzmann’s formula for entropy and statistical distributions, which are necessary but may be unfamiliar to the students, is included. This discussion can also be used independently to introduce some rudiments of statistical physics. In this case, part of the inspiration came from some of Einstein’s papers. We present preliminary, qualitative results obtained with both teachers and selected pupils from various high schools in southern Italy, in the course of several outreach activities. Although the proposal was only tested in this limited context for now, the preliminary results are very promising and they indicate that this proposal can be fruitfully employed for the task.

In the weak-coupling limit approach to open quantum systems, the presence of the bath is eliminated and accounted for by a master equation that introduces dissipative contributions to the system reduced dynamics. Within this framework, there are no bath entropy contributions to the entropy balance. We show that, as a consequence, the entropy production fails to be positive for a class of physically legitimate (i.e., completely positive and trace preserving) non-Markovian dynamical maps. Moreover, in the absence of the semigroup property, if the reduced dynamics has a thermal asymptotic state, this need not be stationary. In this case, even the integrated entropy production becomes negative. These observations imply that, when the conditions leading to reduced dynamics of semigroup type are relaxed, a consistent formulation of the second law of thermodynamics requires that the environment contribution to the entropy balance be explicitly taken into account., 10 pages, 1 figure, accepted in Scientific Reports

Quantum nanoelectronics is in a phase of great expansion, supported mainlyby the development of quantum computing. A high degree of precision isrequired to achieve current objectives, but on the other hand, the experi-ences are also more complex than ever. Nuremical tools seem necessary toachieve the required understanding while dealing with such complexity. Thetime scales involved are getting shorter and are getting closer to the intrinsicquantum time scales of the device, such as time of flight. Our group’s pre-vious work has simulated time-dependent electron transport on a quantumscale. This thesis aims to improve the previous algorithms to obtain greateraccuracy and a better description of the systems by including the electronicenvironment. This work is divided into three main areas. First, we improveof numerical time-dependent simulation tools to take into account an elec-tronic environment in a self-consistent way. The new algorithm can achievearbitrary accuracy in a controlled way. Second, the new algorithm is used todemonstrate the existence of new physical phenomena. We study Josephsonjunctions in different environments to enhance the role of quasi-particles, theeffect of a very short pulse, and to study topological junction characteriza-tion techniques. Finally, various developments are being studied to integratethe phenomenon of decoherence and quantum noise into the simulations.; La nanoélectronique quantique est dans une phase de grande expansion, soutenue principalement par le développement de l'informatique quantique. Une grande précision est nécessaire pour atteindre les objectifs actuels, mais d'un autre côté, les expériences sont aussi plus complexes que jamais. Les outils numériques semblent nécessaires pour réaliser la compréhension exigée tout en traitant une telle complexité. Les échelles de temps concernées sont de plus en plus courtes et se rapprochent des échelles de temps quantiques intrinsèques de l'appareil, comme le temps de vol. Les travaux antérieurs de notre groupe ont simulé le transport d'électrons en fonction du temps à une échelle quantique. Cette thèse vise à améliorer les algorithmes précédents pour obtenir une plus grande précision et une meilleure description des systèmes en incluant l'environnement électronique.Ce travail est divisé en trois domaines principaux. Tout d'abord, nous améliorons les outils de simulation numérique en fonction du temps pour prendre en compte un environnement électronique d'une manière cohérente. Le nouvel algorithme peut atteindre une précision arbitraire d'une manière contrôlée. Deuxièmement, le nouvel algorithme est utilisé pour démontrer l'existence de nouveaux phénomènes physiques. Nous étudions les jonctions Josephson dans différents environnements pour mettre en valeur le rôle des quasi-particules, l'effet d'une impulsion très courte, et pour étudier les techniques de caractérisation de la jonction topologique.Enfin, différents développements sont à l'étude afin d'intégrer le phénomène de décohérence et le bruit quantique dans les simulations.

Quantum nanoelectronics is in a phase of great expansion, supported mainlyby the development of quantum computing. A high degree of precision isrequired to achieve current objectives, but on the other hand, the experi-ences are also more complex than ever. Nuremical tools seem necessary toachieve the required understanding while dealing with such complexity. Thetime scales involved are getting shorter and are getting closer to the intrinsicquantum time scales of the device, such as time of flight. Our group’s pre-vious work has simulated time-dependent electron transport on a quantumscale. This thesis aims to improve the previous algorithms to obtain greateraccuracy and a better description of the systems by including the electronicenvironment. This work is divided into three main areas. First, we improveof numerical time-dependent simulation tools to take into account an elec-tronic environment in a self-consistent way. The new algorithm can achievearbitrary accuracy in a controlled way. Second, the new algorithm is used todemonstrate the existence of new physical phenomena. We study Josephsonjunctions in different environments to enhance the role of quasi-particles, theeffect of a very short pulse, and to study topological junction characteriza-tion techniques. Finally, various developments are being studied to integratethe phenomenon of decoherence and quantum noise into the simulations.; La nanoélectronique quantique est dans une phase de grande expansion, soutenue principalement par le développement de l'informatique quantique. Une grande précision est nécessaire pour atteindre les objectifs actuels, mais d'un autre côté, les expériences sont aussi plus complexes que jamais. Les outils numériques semblent nécessaires pour réaliser la compréhension exigée tout en traitant une telle complexité. Les échelles de temps concernées sont de plus en plus courtes et se rapprochent des échelles de temps quantiques intrinsèques de l'appareil, comme le temps de vol. Les travaux antérieurs de notre groupe ont simulé le transport d'électrons en fonction du temps à une échelle quantique. Cette thèse vise à améliorer les algorithmes précédents pour obtenir une plus grande précision et une meilleure description des systèmes en incluant l'environnement électronique.Ce travail est divisé en trois domaines principaux. Tout d'abord, nous améliorons les outils de simulation numérique en fonction du temps pour prendre en compte un environnement électronique d'une manière cohérente. Le nouvel algorithme peut atteindre une précision arbitraire d'une manière contrôlée. Deuxièmement, le nouvel algorithme est utilisé pour démontrer l'existence de nouveaux phénomènes physiques. Nous étudions les jonctions Josephson dans différents environnements pour mettre en valeur le rôle des quasi-particules, l'effet d'une impulsion très courte, et pour étudier les techniques de caractérisation de la jonction topologique.Enfin, différents développements sont à l'étude afin d'intégrer le phénomène de décohérence et le bruit quantique dans les simulations.

Passive states are special configurations of a quantum system which exhibit no energy decrement at the end of an arbitrary cyclic driving of the model Hamiltonian. When applied to an increasing number of copies of the initial density matrix, the requirement of passivity induces a hierarchical ordering which, in the asymptotic limit of infinitely many elements, pinpoints ground states and thermal Gibbs states. In particular, for large values of N the energy content of a N-passive state which is also structurally stable (i.e. capable to maintain its passivity status under small perturbations of the model Hamiltonian), is expected to be close to the corresponding value of the thermal Gibbs state which has the same entropy. In the present paper we provide a quantitative assessment of this fact, by producing an upper bound for the energy of an arbitrary N-passive, structurally stable state which only depends on the spectral properties of the Hamiltonian of the system. We also show the condition under which our inequality can be saturated. A generalization of the bound is finally presented that, for sufficiently large N, applies to states which are N-passive, but not necessarily structurally stable., Comment: 36 pages, 2 figures. Accepted for publication in Quantum

We present a technique for recovering the spectrum of a non-Markovian bosonic bath and/or non-Markovian noises coupled to an harmonic oscillator. The treatment is valid under the conditions that the environment is large and hot compared to the oscillator, and that its temporal auto-correlation functions are symmetric with respect to time translation and reflection -- criteria which we consider fairly minimal. We model a demonstration of the technique as deployed in the experimental scenario of a nanosphere levitated in a Paul trap, and show that it would effectively probe the spectrum of an electric field noise source from $10^2\,-\,10^6$ Hz with a resolution inversely proportional to the measurement time. This technique may be deployed in quantum sensing, metrology, computing, and in experimental probes of foundational questions, 5 pages plus supplementary

The Lieb-Robinson bound sets a theoretical upper limit on the speed at which information can propagate in non-relativistic quantum spin networks. In its original version, it results in an exponentially exploding function of the evolution time, which is partially mitigated by an exponentially decreasing term that instead depends upon the distance covered by the signal (the ratio between the two exponents effectively defining an upper bound on the propagation speed). In the present paper, by properly accounting for the free parameters of the model, we show how to turn this construction into a stronger inequality where the upper limit only scales polynomially with respect to the evolution time. Our analysis applies to any chosen topology of the network, as long as the range of the associated interaction is explicitly finite. For the special case of linear spin networks we present also an alternative derivation based on a perturbative expansion approach which improves the previous inequality. In the same context we also establish a lower bound to the speed of the information spread which yields a non trivial result at least in the limit of small propagation times., Comment: 10 pages, 5 figures

A generalized multi-parameter Hong-Ou-Mandel interferometer is presented which extends the conventional "Mandel dip" configuration to the case where a symmetric biphoton source is used to monitor the contemporary presence of k independent time-delays. Our construction results in a two-input/two-output setup, obtained by concatenating 50:50 beam splitters with a collection of adjustable achromatic wave-plates. For k=1,2 and k=4 explicit examples can be exhibited that prove the possibility of uniquely linking the zero value of the coincidence counts registered at the output of the interferometer, with the contemporary absence of all the time-delays. Interestingly enough the same result cannot be extended to k=3. Besides, the sensitivity of the interferometer is analyzed when the time-delays are affected by the fluctuations over time-scales that are larger than the inverse of the frequency of the pump used to generate the biphoton state., Comment: 12 pages, 5 figures

In the VIP2 (VIolation of the Pauli Exlusion Principle) experiment at the Gran Sasso underground laboratory (LNGS) we are searching for possible violations of standard quantum mechanics predictions. With high precision we investigate the Pauli Exclusion Principle and the collapse of the wave function (collapse models). We will present our experimental method of searching for possible small violations of the Pauli Exclusion Principle for electrons, via the search for "anomalous" X-ray transitions in copper atoms, produced by "new" electrons (brought inside a copper bar by circulating current) which could have the probability to undergo Pauli-forbidden transition to the ground state (1 s level) already occupied by two electrons. We will describe the concept of the VIP2 experiment taking data at LNGS presently. The goal of VIP2 is to test the PEP for electrons with unprecedented accuracy, down to a limit in the probability that PEP is violated at the level of 10$^{-31}$. We will show preliminary experimental results obtained at LNGS and discuss implications of a possible violation., Comment: Proceedings TAUP 2017

As the possibility to decouple temporal and spatial variations of the electromagnetic field, leading to a wavelength stretching, has been recognized to be of paramount importance for practical applications, we generalize the idea of stretchability from the framework of electromagnetic waves to massive particles. A necessary and sufficient condition which allows one to identify energetically stable configuration of a 1D quantum particle characterized by arbitrary large spatial regions where the associated wave-function exhibit a flat, non-zero profile is presented, together with examples on well-known and widely used potential profiles and an application to 2D models., Comment: 11 pages, 7 figures

In this paper we discuss the implementation of 2-qubit quantum state transfer (QST) in inhomogeneous spin chains where the sender and the receiver blocks are coupled through the bulk channel via weak links. The fidelity and the typical timescale of the QST are discussed as a function of the parameters of the weak links. Given the possibility of implementing with cold atoms in optical lattices a variety of condensed matter systems, including spin systems, we also discuss the possible implementation of the discussed 2-qubit QST with cold gases with weak links, together with a discussion of the applications and limitations of the presented results.

These days there is no educational text for the issue freely available that would be adequate for the students of the course Radiology assistant and for related fields. The work set the following aims: 1. To choose a theory of transmission of the knowledge to the level of the fields mentioned. 2. To create an educational text so that the theory would be respected. 3. To verify the educational text experimentally from the point of view of the students'possibilities. 4. To apply selected statistical methods. Based on the present analysis of the issue and set aims the following hypotheses were formulated: 1. The educational text for radiology assistants can be created through the application of curricular process. 2. The knowledge of the students acquiered through the developed educational system will be divided in a similar way as it is divided normally. The aims mentioned above were accomplished thanks to use of all the aspects of the curricular process. Based on this process it was first necessary to analyse the current scientific system of classical and quantum physics. Adjusted physical knowledge were written up into an adequate educational text for radiology assistants. The hypothesis that an educational text for radiology assistants can be created through the application of the curricural process was verified. The text was provided electronically to the students of South Bohemian University and to radiology assistants. A test of 15 questions was created to verify the knowledge acquired by students. The educational test was also provided electronically. The results were then processed statistically. It was made use of methods of descriptive statistics, but also of nonparametrical testing of hypotheses. It was found out that the knowledge of the students can be described with Gaussian division based on the nonparametrical testing. Thanks to this the adequacy of the text and the second hypothesis that the knowledge of the students acquired through the developed educational system would be divided in a similar way as it is divided normally were verified.

The Schr\"odinger-Newton equation has gained attention in the recent past as a nonlinear modification of the Schr\"odinger equation due to a gravitational self-interaction. Such a modification is expected from a fundamentally semi-classical theory of gravity, and can therefore be considered a test case for the necessity of the quantisation of the gravitational field. Here we provide a thorough study of the effects of the Schr\"odinger-Newton equation for a micron-sized sphere trapped in a harmonic oscillator potential. We discuss both the effect on the energy eigenstates and the dynamical behaviour of squeezed states, covering the experimentally relevant parameter regimes., Comment: 22 pages, 14 figures

The concept of quantum correlation matrix for observables leads to the application of the PCA (Principal Component Analysis) also for quantum system in Hilbert space. It is shown that, in the case of a 2x2 spin system where the observables are the Pauli matrices and a polarization vector is acting on the density matrix, meaningful results can be obtained by the PCA in terms of qubit properties. In particular, it is shown that by choosing, for example, the (x,z) spinors, the axes of the principal components (PC) coincide with the circular polarization basis on the Block Sphere.

Fluctuations of the atomic positions are at the core of a large class of unusual material properties ranging from quantum para-electricity to high temperature superconductivity. Their measurement in solids is the subject of an intense scientific debate focused on seeking a methodology capable of establishing a direct link between the variance of the atomic displacements and experimentally measurable observables. Here we address this issue by means of non-equilibrium optical experiments performed in shot-noise limited regime. The variance of the time dependent atomic positions and momenta is directly mapped into the quantum fluctuations of the photon number of the scattered probing light. A fully quantum description of the non-linear interaction between photonic and phononic fields is benchmarked by unveiling the squeezing of thermal phonons in $\alpha$-quartz., Comment: 7 pages (main text), 5 figures, 11 pages (supplementary information)

Do the laws of quantum physics still hold for macroscopic objects - this is at the heart of Schr\"odinger's cat paradox - or do gravitation or yet unknown effects set a limit for massive particles? What is the fundamental relation between quantum physics and gravity? Ground-based experiments addressing these questions may soon face limitations due to limited free-fall times and the quality of vacuum and microgravity. The proposed mission MAQRO may overcome these limitations and allow addressing those fundamental questions. MAQRO harnesses recent developments in quantum optomechanics, high-mass matter-wave interferometry as well as state-of-the-art space technology to push macroscopic quantum experiments towards their ultimate performance limits and to open new horizons for applying quantum technology in space. The main scientific goal of MAQRO is to probe the vastly unexplored "quantum-classical" transition for increasingly massive objects, testing the predictions of quantum theory for truly macroscopic objects in a size and mass regime unachievable in ground-based experiments. The hardware for the mission will largely be based on available space technology. Here, we present the MAQRO proposal submitted in response to the (M4) Cosmic Vision call of the European Space Agency for a medium-size mission opportunity with a possible launch in 2025., Comment: 38 pages, 10 tables, 23 figures

We present a quantifier of non-classical correlations for bipartite, multi-mode Gaussian states. It is derived from the Discriminating Strength measure, introduced for finite dimensional systems in A. Farace et al., New. J. Phys. 16, 073010 (2014). As the latter the new measure exploits the Quantum Chernoff Bound to gauge the susceptibility of the composite system with respect to local perturbations induced by unitary gates extracted from a suitable set of allowed transformations (the latter being identified by posing some general requirements). Closed expressions are provided for the case of two-mode Gaussian states obtained by squeezing or by linearly mixing via a beam-splitter a factorized two-mode thermal state. For these density matrices, we study how non-classical correlations are related with the entanglement present in the system and with its total photon number., 11+6 pages, 4 figures

We search for the optimal quantum pure states of identical bosonic particles for applications in quantum metrology, in particular in the estimation of a single parameter for the generic two-mode interferometric setup. We consider the general case in which the total number of particles is fluctuating around an average $N$ with variance $\Delta N^2$. By recasting the problem in the framework of classical probability, we clarify the maximal accuracy attainable and show that it is always larger than the one reachable with a fixed number of particles (i.e., $\Delta N=0$). In particular, for larger fluctuations, the error in the estimation diminishes proportionally to $1/\Delta N$, below the Heisenberg-like scaling $1/N$. We also clarify the best input state, which is a "quasi-NOON state" for a generic setup, and for some special cases a two-mode "Schr\"odinger-cat state" with a vacuum component. In addition, we search for the best state within the class of pure Gaussian states with a given average $N$, which is revealed to be a product state (with no entanglement) with a squeezed vacuum in one mode and the vacuum in the other., Comment: 13 pages, 4 figures

International audience; In the VIP (VIolation of Pauli exclusion principle) and its follow-up VIP-2 experiments at the Laboratori Nazionali del Gran Sasso, we test the validity of the Pauli Exclusion Principle, by searching for x-rays from copper atomic transitions from a 2p orbit electron to the ground state which is already occupied by two electrons. Such transitions are prohibited by the Pauli Exclusion Principle. The physics run of the VIP-2 experiment started in late 2016 and will collect data for three years. From the first data taking period of two months we have obtained a new limit better than the VIP result from three years of running. In this article we present the published first physics result from the VIP-2 experiment and discuss about the future perspectives. © The Authors, published by EDP Sciences.

We study the dynamics of heat flux in the thermalization process of a pair of identical quantum systems that interact dissipatively with a reservoir in a cascaded fashion. Despite that the open dynamics of the bipartite system $S$ is globally Lindbladian, one of the subsystems ``sees'' the reservoir in a state modified by the interaction with the other subsystem and hence it undergoes a non-Markovian dynamics. As a consequence, the heat flow exhibits a nonexponential time behavior which can greatly deviate from the case where each party is independently coupled to the reservoir. We investigate both thermal and correlated initial states of $S$ and show that the presence of correlations at the beginning can considerably affect the heat-flux rate. We carry out our study in two paradigmatic cases---a pair of harmonic oscillators with a reservoir of bosonic modes and two qubits with a reservoir of fermionic modes---and compare the corresponding behaviors. In the case of qubits and for initial thermal states, we find that the trace distance discord is at any time interpretable as the correlated contribution to the total heat flux.

The "problem of time" in present physics substantially consists in the fact that a straightforward quantization of the general relativistic evolution equation and constraints generates for the Universe wave function the Wheeler-De Witt equation, which describes a static Universe. Page and Wootters considered the fact that there exist states of a system composed by entangled subsystems that are stationary, but one can interpret the component subsystems as evolving: this leads them to suppose that the global state of the universe can be envisaged as one of this static entangled state, whereas the state of the subsystems can evolve. Here we synthetically present an experiment, based on PDC polarization entangled photons, that allows showing with a practical example a situation where this idea works, i.e. a subsystem of an entangled state works as a "clock" of another subsystem. The ”problem of time” in present physics substantially consists in the fact that a straightforward quantization of the general relativistic evolution equation and constraints generates for the Universe wave function the Wheeler-De Witt equation, which describes a static Universe. Page and Wootters considered the fact that there exist states of a system composed by entangled subsystems that are stationary, but one can interpret the component subsystems as evolving: this leads them to suppose that the global state of the universe can be envisaged as one of this static entangled state, whereas the state of the subsystems can evolve. Here we synthetically present an experiment, based on PDC polarization entangled photons, that shows a practical example where this idea works, i.e. a subsystem of an entangled state works as a ”clock” of another subsystem.

An all-optical scheme for simulating non-Markovian evolution of a quantum system is proposed. It uses only linear optics elements and by controlling the system parameters allows one to control the presence or absence of information backflow from the environment. A sufficient and necessary condition for the non-Markovianity of our channel based on Gaussian inputs is proved. Various criteria for detecting non-Markovianity are also investigated by checking the dynamical evolution of the channel., 7 figures. Typos are corrected and new reference is added

We study optimal control strategies to optimize the relaxation rate towards the fixed point of a quantum system in the presence of a non-Markovian dissipative bath. Contrary to naive expectations that suggest that memory effects might be exploited to improve optimal control effectiveness, non-Markovian effects influence the optimal strategy in a non trivial way: we present a necessary condition to be satisfied so that the effectiveness of optimal control is enhanced by non-Markovianity subject to suitable unitary controls. For illustration, we specialize our findings for the case of the dynamics of single qubit amplitude damping channels. The optimal control strategy presented here can be used to implement optimal cooling processes in quantum technologies and may have implications in quantum thermodynamics when assessing the efficiency of thermal micro-machines., Comment: 7 pages, 3 figures

We propose a technique that enables the creation of quantum discord between two distant nodes, each containing a cavity consisting of the Bose-Einstein condensate (BEC), by applying a nonideal Bell-like detection on the output modes of optical cavities. We find the covariance matrix of the system after the nonideal Bell-like detection, showing explicitly that one enables manipulation of the quantum correlations, and particularly quantum discord, between remote BECs. We also find that the nonideal Bell-like detection can create entanglement between distant BECs at the two remote sites. (C) 2015 Optical Society of America

The problem of estimating a parameter of a quantum system through a series of measurements performed sequentially on a quantum probe is analyzed in the general setting where the underlying statistics is explicitly non-i.i.d. We present a generalization of the central limit theorem in the present context, which under fairly general assumptions shows that as the number $N$ of measurement data increases the probability distribution of functionals of the data (e.g., the average of the data) through which the target parameter is estimated becomes asymptotically normal and independent of the initial state of the probe. At variance with the previous studies [M. Gu\c{t}\u{a}, Phys. Rev. A 83, 062324 (2011); M. van Horssen and M. Gu\c{t}\u{a}, J. Math. Phys. 56, 022109 (2015)] we take a diagrammatic approach, which allows one to compute not only the leading orders in $N$ of the moments of the average of the data but also those of the correlations among subsequent measurement outcomes. In particular our analysis points out that the latter, which are not available in usual i.i.d. data, can be exploited in order to improve the accuracy of the parameter estimation. An explicit application of our scheme is discussed by studying how the temperature of a thermal reservoir can be estimated via sequential measurements on a quantum probe in contact with the reservoir., Comment: 20 pages, 10 figures

We study two different models of optomechanical systems where a temperature gradient between two radiation baths is exploited for inducing self-sustained coherent oscillations of a mechanical resonator. Viewed from a thermodynamic perspective, such systems represent quantum instances of self-contained thermal machines converting heat into a periodic mechanical motion and thus they can be interpreted as nano-scale analogues of macroscopic piston engines. Our models are potentially suitable for testing fundamental aspects of quantum thermodynamics in the laboratory and for applications in energy efficient nanotechnology., 10 pages, 6 figures

The long-standing conjectures of the optimality of Gaussian inputs for Gaussian channel and Gaussian additivity are solved for a broad class of covariant or contravariant Bosonic Gaussian channels (which includes in particular thermal, additive classical noise, and amplifier channels) restricting to the class of states with finite second moments. We show that the vacuum is the input state which minimizes the entropy at the output of such channels. This allows us to show also that the classical capacity of these channels (under the input energy constraint) is additive and is achieved by Gaussian encodings.

We give a consistent quantum description of time, based on Page and Wootters' conditional probabilities mechanism, that overcomes the criticisms that were raised against similar previous proposals. In particular we show how the model allows to reproduce the correct statistics of sequential measurements performed on a system at different times., Final version accepted for publication on Phys. Rev. D

1 ar X iv :1 50 1. 04 46 2v 1 [ qu an tph ] 1 9 Ja n 20 15 The development of mathematically complete and consistent models solving the so-called ”measurement problem”, strongly renewed the interest of the scientific community for the foundations of quantum mechanics, among these the Dynamical Reduction Models posses the unique characteristic to be experimentally testable. In the first part of the paper an upper limit on the reduction rate parameter of such models will be obtained, based on the analysis of the X-ray spectrum emitted by an isolated slab of germanium and measured by the IGEX experiment. The second part of the paper is devoted to present the results of the VIP (Violation of the Pauli exclusion principle) experiment and to describe its recent upgrade. The VIP experiment established a limit on the probability that the Pauli Exclusion Principle (PEP) is violated by electrons, using the very clean method of searching for PEP forbidden atomic transitions in copper. 1 Upper limit on the wave function collapse mean rate parameter λ The first consistent and satisfying Dynamical Reduction Model, known as Quantum Mechanics with Spontaneous Localization (QMSL) [1], considers particles undergoing spontaneous localizations around definite positions, following a Possion distribution characterized by a mean frequency λ = 10−16 s−1. This brought to the development of the CSL theory [2] based on the introduction of new, non linear and stochastic terms, in the Shrodinger equation besides to the standard Hamiltonian. Such terms induce, for the state vector, a diffusion process, which is responsible for the wave packet reduction. As demonstrated by Q. Fu [3] the particle interaction with the stochastic field also causes an enhancement of the energy expectation value. This implies, for a charged particle, the emission of electromagnetic radiation (known as spontaneous radiation) not present in the standard quantum mechanics. The radiation spectrum spontaneously emitted by a free electron was calculated by Fu [3] in the framework of the non-relativistic CSL model, and it is given by: dΓ(E) dE = eλ 4π2a2m2E , where m represents the electron mass, E is the energy of the emitted photon, λ and a are respectively the reduction rate parameter and the correlation length of the reduction model which is assumed to be a = 10−7 m. If the stochastic field is assumed to be coupled to the particle mass density (mass proportional CSL model) (see for example [4]) then the previous expression for the emission rate is to be multiplied by the factor (me/mN ) , with mN the nucleon mass. Using the measured radiation appearing in an isolated slab of Germanium [5] corresponding to an energy of 11 KeV, Fu obtained the limit λ ≤ 0.55 · 10−16s−1. In Ref. [6] the author argues that, in evaluating his numerical result, Fu uses for the electron charge the value e = 17137.04, whereas the standard adopted Feynman rules require the identification e/(4π) = 17137.04. We took into account this correction when evaluating the new limit. In order to reduce possible biases introduced on the λ value by the punctual evaluation of the rate at one single energy bin, the X-ray emission spectrum measured by the IGEX experiment [7, 8] was fitted in the range ∆E = 4.5÷ 48.5 KeV m, compatible with the non-relativistic assumption (for electrons) used in the calculation of the predicted rate. A Bayesian model was

We study a set of new functionals (called entanglement--breaking indices) which characterize how many local iterations of a given (local) quantum channel are needed in order to completely destroy the entanglement between the system of interest over which the transformation is defined and an external ancilla. The possibility of contrasting the noisy effects introduced by the channel iterations via the action of intermediate ({\it filtering}) transformations is analyzed. We provide some examples in which our functionals can be exactly calculated. The differences between unitary and non-unitary filtering operations are analyzed showing that, at least for systems of dimension $d$ larger than or equal to 3, the non-unitary choice is preferable (the gap between the performances of the two cases being divergent in some cases). For $d=2$ (qubit case) on the contrary no evidences of the presence of such gap is revealed: we conjecture that for this special case unitary filtering transformations are optimal. The scenario in which more general filtering protocols are allowed is also discussed in some detail. The case of a depolarizing noise acting on a two--qubit system is exactly solved in a general case., 17 pages, 2 figures. A new section on generalized filtering protocols has been added

The ability of quantum systems to host exponentially complex dynamics has the potential to revolutionize science and technology. Therefore, much effort has been devoted to developing of protocols for computation, communication and metrology, which exploit this scaling, despite formidable technical difficulties. Here we show that the mere frequent observation of a small part of a quantum system can turn its dynamics from a very simple one into an exponentially complex one, capable of universal quantum computation. After discussing examples, we go on to show that this effect is generally to be expected: almost any quantum dynamics becomes universal once ‘observed’ as outlined above. Conversely, we show that any complex quantum dynamics can be ‘purified’ into a simpler one in larger dimensions. We conclude by demonstrating that even local noise can lead to an exponentially complex dynamics., It is an old adage in quantum physics that the observation of a system changes its properties, as exemplified by the quantum Zeno effect. Now, Burgarth et al. show that such repeated measurement of a quantum system actually enriches its dynamics, letting it explore a much larger algebra than it did before.

A new measure of non-classical correlations is introduced and characterized. It tests the ability of using a state {\rho} of a composite system AB as a probe for a quantum illumination task [e.g. see S. Lloyd, Science 321, 1463 (2008)], in which one is asked to remotely discriminate among the two following scenarios: i) either nothing happens to the probe, or ii) the subsystem A is transformed via a local unitary R_A whose properties are partially unspecified when producing {\rho}. This new measure can be seen as the discrete version of the recently introduced Intereferometric Power measure [G. Girolami et al. e-print arXiv:1309.1472 (2013)] and, at least for the case in which A is a qubit, it is shown to coincide (up to an irrelevant scaling factor) with the Local Quantum Uncertainty measure of D. Girolami, T. Tufarelli, and G. Adesso, Phys. Rev. Lett. 110, 240402 (2013). Analytical expressions are derived which allow us to formally prove that, within the set of separable configurations, the maximum value of our non-classicality measure is achieved over the set of quantum-classical states (i.e. states {\rho} which admit a statistical unravelling where each element of the associated ensemble is distinguishable via local measures on B)., Comment: 11+2 pages, 2+1 figures

In previous years several theoretical papers discussed if time can be an emergent property deriving from quantum correlations. Here, to provide insight into how this phenomenon can occur, we present an experiment that illustrates Page and Wootters' mechanism of "static" time [D. N. Page and W. K. Wootters, Phys. Rev. D 27, 2885 (1983)0556-282110.1103/PhysRevD.27.2885], and Gambini et al. for subsequent refinements [R. Gambini, Phys. Rev. D 79, 041501(R) (2009)PRVDAQ1550-799810.1103/PhysRevD.79.041501]. A static, entangled state between a clock system and the rest of the universe is perceived as evolving by internal observers that test the correlations between the two subsystems. We implement this mechanism using an entangled state of the polarization of two photons, one of which is used as a clock to gauge the evolution of the second: An "internal" observer that becomes correlated with the clock photon sees the other system evolve, while an "external" observer that only observes global properties of the two photons can prove it is static. © 2014 American Physical Society.

Spontaneous synchronization is a fundamental phenomenon, important in many theoretical studies and applications. Recently this effect has been analyzed and observed in a number of physical systems close to the quantum mechanical regime. In this work we propose the mutual information as a useful order parameter which can capture the emergence of synchronization in very different contexts, ranging from semi-classical to intrinsically quantum mechanical systems. Specifically we first study the synchronization of two coupled Van der Pol oscillators in both classical and quantum regimes and later we consider the synchronization of two qubits inside two coupled optical cavities. In all these contexts, we find that mutual information can be used as an appropriate figure of merit for determining the synchronization phases, independently of the specific details of the system.

Optical channels, such as fibers or free-space links, are ubiquitous in today's telecommunication networks. They rely on the electromagnetic field associated with photons to carry information from one point to another in space. As a result, a complete physical model of these channels must necessarily take quantum effects into account in order to determine their ultimate performances. Specifically, Gaussian photonic (or bosonic) quantum channels have been extensively studied over the past decades given their importance for practical purposes. In spite of this, a longstanding conjecture on the optimality of Gaussian encodings has yet prevented finding their communication capacity. Here, this conjecture is solved by proving that the vacuum state achieves the minimum output entropy of a generic Gaussian bosonic channel. This establishes the ultimate achievable bit rate under an energy constraint, as well as the long awaited proof that the single-letter classical capacity of these channels is additive. Beyond capacities, it also has broad consequences in quantum information sciences.

We consider the problem of time-optimal control of a continuous bosonic quantum system subject to the action of a Markovian dissipation. In particular, we consider the case of a one-mode Gaussian quantum system prepared in an arbitrary initial state and which relaxes to the steady state due to the action of the dissipative channel. We assume that the unitary part of the dynamics is represented by Gaussian operations which preserve the Gaussian nature of the quantum state, i.e., arbitrary phase rotations, bounded squeezing, and unlimited displacements. In the ideal ansatz of unconstrained quantum control (i.e., when the unitary phase rotations, squeezing, and displacement of the mode can be performed instantaneously), we study how control can be optimized for speeding up the relaxation towards the fixed point of the dynamics and we analytically derive the optimal relaxation time. Our model has potential and interesting applications to the control of modes of electromagnetic radiation and of trapped levitated nanospheres.

Recently, the longstanding Gaussian optimizer conjecture was proven for bosonic Gaussian gauge-covariant or contravariant channels in the work of Giovannetti, Holevo and Garcia-Patron [3]. In the paper of Mari, Giovannetti and Holevo [11] this result was strengthened for one-mode channels by establishing that the output for the vacuum or coherent input majorizes the output for any other input. In the present paper we give the multimode extension of the result of [11], including sufficient conditions under which the coherent states are the only optimizers. We also discuss direct implications of this multimode majorization result to the positive solution of the additivity problem for the Gaussian channels. In particular, we demonstrate the additivity of the output Renyi entropies of arbitrary order p>1. Finally, we present an alternative derivation of a majorization property of Glauber's coherent states by Lieb and Solovej [10], basing on the method of the work [3]., Sec. 6 with the proof of attainability of the infimum in question is added

Quantum communication theory explores the implications of quantum mechanics to the tasks of information transmission. Many physical channels can be formally described as quantum Gaussian operations acting on bosonic quantum states. Depending on the input state and on the quality of the channel, the output suffers certain amount of noise. For a long time it has been conjectured, but never proved, that output states of Gaussian channels corresponding to coherent input signals are the less noisy ones (in the sense of a majorization criterion). In this work we prove this conjecture. Specifically we show that every output state of a phase insensitive Gaussian channel is majorized by the output state corresponding to a coherent input. The proof is based on the optimality of coherent states for the minimization of strictly concave output functionals. Moreover we show that coherent states are the unique optimizers., 7 pages, 1 figure. Published version

This PhD entitled "Nanoscale structuration effect on the phonon transport at low temperature" take place for three years in the Thermodynamique et Biophysique des Petits Systèmes of the Institut Néel.The context of this PhD is to understand and control the heat transport in samples with variations at the nanoscale. These samples were mostly suspended silicon nanowires. The production was performed in the Néel Institute. During these three years, three important results have been demonstrated.First, we verify that heat transport is not dominated by an effect due to the contact between the suspended nanowire and the thermal bath. This has been demonstrated by the agreement between the measurements and the model called Casimir-Ziman. It was also mainly verified with wires whose junction to the thermal bath has been adapted to allow transmission close to unity. These profiles nanowires have the same thermal conductance as a nanowire with abrupt junction to the thermal bath. This proves that the transmission is always close to 1.Then measurements on nanowires whose section is corrugated have shown a reduction in thermal conductance. This reduction is explained by the presence of backscatter phonons at the surface, resulting in a large reduction of their mean free path. Thus, the phonons in a smooth nanowire have a mean free path up to 9 times greater than in these corrugated nanowires. Simulations with the Monte-Carlo method also demonstrate this effect.If these first results were achieved for monocrystalline silicon nanowires, my last work has focused on the study sample of silicon nitride. This material is an amorphous one. Physics of heat transport in amorphous materials is not yet fully understood. However, measurements on these materials show a similar behavior, both qualitatively and quantitatively, for almost all amorphous materials. We have measured samples of different kinds, to see if this behavior was still valid when the sample size is reduced. The result of our measurements is that the size plays a role in transport. As in crystalline materials, the small sample size will limit the heat transport. However transport in low-dimensional samples shows the same behavior qualitatively as in bulk amorphous materials. This can help provide clues for understanding the heat transport in amorphous materials.In conclusion, this work has allowed me to make and measure the heat transport in different types of samples. The results allow a better knowledge of the phonon transport, thus helping to pave the way towards a better control of heat transport., Cette thèse, intitulé « Effet de structuration à l'échelle du nanomètre sur le transport de phonon à basse température » c'est déroulé pendant trois ans au sein du groupe Thermodynamique et Biophysique des Petits Systèmes de l'Institut Néel.Il s'agit de comprendre et de contrôler le transport de chaleur au sein d'échantillons ayant des variations de l'ordre du nanomètre. Ces échantillons ont surtout été des nanofils suspendus en silicium. La fabrication a été réalisée au sein de l'Institut Néel. Lors de ces trois années, trois résultats importants ont été réalisés.Tout d'abord, il a fallu vérifier que le transport de chaleur ne soit pas dominé par un effet dû aux contacts entre le nanofil suspendu et le bain thermique. Cela a pu être mis en évidence grâce à la concordance entre les mesures et le modèle appelé Casimir-Ziman. Mais cela a surtout été vérifié avec des fils dont la jonction au bain thermique a été adaptée afin de permettre une transmission proche de l'unité. Ces fils profilés ayant la même conductance thermique que les fils avec une jonction abrupte au bain thermique, cela prouve que la transmission est toujours proche de 1.Ensuite des mesures sur des fils dont la section est ondulée ont permis de montrer une réduction de la conductance thermique. Cette réduction est expliquée par la présence de rétrodiffusion des phonons à la surface, ce qui entraîne une grande réduction de leur libre parcours moyen. Ainsi, les phonons dans un nanofil droit ont un libre parcours moyen jusqu'à 9 fois plus grand que dans ces nanofils à la section ondulée. Des simulations avec la méthode de Monte-Carlo ont permis de mettre en évidence cet effet.Si ces premiers résultats ont été réalisés pour des fils de silicium monocristallin, le dernier travail a porté sur l'étude d'échantillon en nitrure de silicium. Ce matériau est un matériau amorphe. La physique du transport de chaleur au sein des matériaux amorphes n'est pas encore complètement comprise. Cependant les mesures faites sur ces matériaux montrent un comportement similaire, tant qualitatif que quantitatif, pour presque tous les matériaux amorphes. Nous avons donc mesurés des échantillons de différentes sortes, afin de vérifier si ce comportement était toujours valable, lorsque la dimension de l'échantillon est réduite. Le résultat de nos mesures est que la dimension joue un rôle sur le transport. Tout comme dans les matériaux cristallins, la basse dimension de l'échantillon va limiter le transport de chaleur. Cependant le transport dans les échantillons de basses dimensions montre le même comportement qualitatif que les matériaux amorphes massifs. Ce travail peut permettre de donner des pistes pour la compréhension du transport de chaleur au sein des matériaux amorphes.En conclusion ce travail m'a permis de fabriquer puis de mesurer le transport de chaleur dans différents types d'échantillons. Les résultats obtenus permettent une meilleur connaissance du transport des phonons, et donc aident à ouvrir la voie vers un meilleur contrôle du transport de la chaleur.

This PhD entitled "Nanoscale structuration effect on the phonon transport at low temperature" take place for three years in the Thermodynamique et Biophysique des Petits Systèmes of the Institut Néel.The context of this PhD is to understand and control the heat transport in samples with variations at the nanoscale. These samples were mostly suspended silicon nanowires. The production was performed in the Néel Institute. During these three years, three important results have been demonstrated.First, we verify that heat transport is not dominated by an effect due to the contact between the suspended nanowire and the thermal bath. This has been demonstrated by the agreement between the measurements and the model called Casimir-Ziman. It was also mainly verified with wires whose junction to the thermal bath has been adapted to allow transmission close to unity. These profiles nanowires have the same thermal conductance as a nanowire with abrupt junction to the thermal bath. This proves that the transmission is always close to 1.Then measurements on nanowires whose section is corrugated have shown a reduction in thermal conductance. This reduction is explained by the presence of backscatter phonons at the surface, resulting in a large reduction of their mean free path. Thus, the phonons in a smooth nanowire have a mean free path up to 9 times greater than in these corrugated nanowires. Simulations with the Monte-Carlo method also demonstrate this effect.If these first results were achieved for monocrystalline silicon nanowires, my last work has focused on the study sample of silicon nitride. This material is an amorphous one. Physics of heat transport in amorphous materials is not yet fully understood. However, measurements on these materials show a similar behavior, both qualitatively and quantitatively, for almost all amorphous materials. We have measured samples of different kinds, to see if this behavior was still valid when the sample size is reduced. The result of our measurements is that the size plays a role in transport. As in crystalline materials, the small sample size will limit the heat transport. However transport in low-dimensional samples shows the same behavior qualitatively as in bulk amorphous materials. This can help provide clues for understanding the heat transport in amorphous materials.In conclusion, this work has allowed me to make and measure the heat transport in different types of samples. The results allow a better knowledge of the phonon transport, thus helping to pave the way towards a better control of heat transport.; Cette thèse, intitulé « Effet de structuration à l'échelle du nanomètre sur le transport de phonon à basse température » c'est déroulé pendant trois ans au sein du groupe Thermodynamique et Biophysique des Petits Systèmes de l'Institut Néel.Il s'agit de comprendre et de contrôler le transport de chaleur au sein d'échantillons ayant des variations de l'ordre du nanomètre. Ces échantillons ont surtout été des nanofils suspendus en silicium. La fabrication a été réalisée au sein de l'Institut Néel. Lors de ces trois années, trois résultats importants ont été réalisés.Tout d'abord, il a fallu vérifier que le transport de chaleur ne soit pas dominé par un effet dû aux contacts entre le nanofil suspendu et le bain thermique. Cela a pu être mis en évidence grâce à la concordance entre les mesures et le modèle appelé Casimir-Ziman. Mais cela a surtout été vérifié avec des fils dont la jonction au bain thermique a été adaptée afin de permettre une transmission proche de l'unité. Ces fils profilés ayant la même conductance thermique que les fils avec une jonction abrupte au bain thermique, cela prouve que la transmission est toujours proche de 1.Ensuite des mesures sur des fils dont la section est ondulée ont permis de montrer une réduction de la conductance thermique. Cette réduction est expliquée par la présence de rétrodiffusion des phonons à la surface, ce qui entraîne une grande réduction de leur libre parcours moyen. Ainsi, les phonons dans un nanofil droit ont un libre parcours moyen jusqu'à 9 fois plus grand que dans ces nanofils à la section ondulée. Des simulations avec la méthode de Monte-Carlo ont permis de mettre en évidence cet effet.Si ces premiers résultats ont été réalisés pour des fils de silicium monocristallin, le dernier travail a porté sur l'étude d'échantillon en nitrure de silicium. Ce matériau est un matériau amorphe. La physique du transport de chaleur au sein des matériaux amorphes n'est pas encore complètement comprise. Cependant les mesures faites sur ces matériaux montrent un comportement similaire, tant qualitatif que quantitatif, pour presque tous les matériaux amorphes. Nous avons donc mesurés des échantillons de différentes sortes, afin de vérifier si ce comportement était toujours valable, lorsque la dimension de l'échantillon est réduite. Le résultat de nos mesures est que la dimension joue un rôle sur le transport. Tout comme dans les matériaux cristallins, la basse dimension de l'échantillon va limiter le transport de chaleur. Cependant le transport dans les échantillons de basses dimensions montre le même comportement qualitatif que les matériaux amorphes massifs. Ce travail peut permettre de donner des pistes pour la compréhension du transport de chaleur au sein des matériaux amorphes.En conclusion ce travail m'a permis de fabriquer puis de mesurer le transport de chaleur dans différents types d'échantillons. Les résultats obtenus permettent une meilleur connaissance du transport des phonons, et donc aident à ouvrir la voie vers un meilleur contrôle du transport de la chaleur.

This paper aims at supporting the claim that some forms of hyper-simplification, by making physics seem easy, are at risk of dangerously distorting the content as well as the process of learning physics. The paper presents examples of dangerous simplifications in the teaching of quantum physics. Then, examples of productive forms of complexity are discussed, both as criteria for designing teaching proposals, and for realizing appropriate learning environments, namely properly complex territories. Empirical results, from a teaching/learning experiment on quantum physics at upper secondary school (grade 13), are reported. These results show examples of students’ reactions to travelling through a complex territory, and allow us to argue that unavoidable difficulty in learning quantum physics can be transformed into cultural challenges within reach of secondary school students.

The conflict between classical and quantum physics can be identified through a series of yes-no tests on quantum systems, without it being necessary that these systems be in special quantum states. Kochen-Specker (KS) sets of yes-no tests have this property and provide a quantum-versus-classical advantage that is free of the initialization problem that affects some quantum computers. Here, we report the first experimental implementation of a complete KS set that consists of 18 yes-no tests on four-dimensional quantum systems and show how to use the KS set to obtain a state-independent quantum advantage. We first demonstrate the unique power of this KS set for solving a task while avoiding the problem of state initialization. Such a demonstration is done by showing that, for 28 different quantum states encoded in the orbital-angular-momentum and polarization degrees of freedom of single photons, the KS set provides an impossible-to-beat solution. In a second experiment, we generate maximally contextual quantum correlations by performing compatible sequential measurements of the polarization and path of single photons. In this case, state independence is demonstrated for 15 different initial states. Maximum contextuality and state independence follow from the fact that the sequences of measurements project any initial quantum state onto one of the KS set's eigenstates. Our results show that KS sets can be used for quantum-information processing and quantum computation and pave the way for future developments., REVTeX, 15 pages, 4 figures

This research aims at the application of the models extracted from the many-body quantum mechanics to describe social dynamics. It is intended to draw macroscopic characteristics of communities starting from the analysis of microscopic interactions with respect to the node model. In the aim to experiment the validity of the proposed mathematical model, the Q.NET project is intended to define an open-source platform able to model nodes and interactions of a network, to simulate its behaviour starting from specific defined models. Q.NET project will allow to visualize the macroscopic results emerging during the analysis and simulation phases through a digital representation of the social network.

[Excerpt from the Introduction]: This thesis focuses on neutral excitations of few-electrons states in nanofabricatedQDsmeasured by inelastic light scattering. The analysis of the spectra demonstrate that this technique can open a venue in the study of quasi-particles at the nanoscale. A model of electronic states confined in QDs is presented in the first chapter, while the second one provides a survey of the relevant experimental studies in this field. Special attention is paid to the process of inelastic light scattering by introducing a description of the selection rules for the scattering processes by electrons in semiconductor QDs. Chapter 3 describes the nano-fabrication techniques of doped AlGaAs/GaAs QDs and the different setups used for the measurements. Experiments performedwith μ-photoluminescence that demonstrate the confinement and the homogeneity of the fabricated QDs are reported at the end of this chapter. Chapter 4 reports inelastic light scattering spectra fromQDs with many electrons. In these experiments the atomic-like shell structure of the electronic states is demonstrated. The framework used to describe this regime of highly populated QDs is similar to the one used for transport experiments in the Coulomb blockade regime.Observations of tunneling excitations in coupled quantumdots with inelastic light scattering will also be presented. The most innovative results of this work are presented in chapter 5 that focuses on the study of interaction phenomena that take place in QDs in the few electron regime. The correlations that occur among the electrons deeply affect the inelastic light spectra in these systems. Themain outcome regards the case of QDs with four electrons where strong correlation effects have been found in the behavior of spin and charge collective excitations. Light scattering spectra from these dots at zero and finite perpendicularmagnetic fieldswill be presented. The evaluation of the excitation spectra as a function of the magnetic field reveals a ground-state transition between correlated states of the four electrons with different spin configurations.