État fondamental

L'état fondamental est, en physique, une notion polysémique renvoyant généralement à un état de plus basse énergie pour un électron, ou de plus grande neutralité électrique pour un atome.vignette|Différents niveaux d'énergie d'un électron dans un atome : l'état fondamental et les états excités. Après avoir absorbé de l'énergie, un électron peut passer de l'état fondamental à un état excité de plus haute énergie. Physique quantique En physique quantique, les états fondamentaux d'un système sont les états quantiques de plus basse énergie. Tout état d'énergie supérieure à celle des états fondamentaux est un état excité. S'il existe plusieurs états excités correspondant à un même niveau d'énergie, ces derniers sont dits dégénérés. L'orbitale la plus stable ou état fondamental de l'atome d'hydrogène est celle dont l'énergie est la plus basse, E= . Autres acceptions On désigne parfois par état fondamental d'un élément chimique, l'état électriquement

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Électron

L'électron, un des composants de l'atome avec les neutrons et les protons, est une particule élémentaire qui possède une charge élémentaire de signe négatif. Il est fondamental en chimie, car il part

Fonction d'onde

thumb|300px|right|Illustration de la notion de fonction d'onde dans le cas d'un oscillateur harmonique. Le comportement en mécanique classique est représenté sur les images A et B et celui en mécaniqu

Spin

Le 'spin' () est, en physique quantique, une des propriétés internes des particules, au même titre que la masse ou la charge électrique. Comme d'autres observables quantiques, sa mesure donne des val

PHYS-462: Quantum transport in mesoscopic systems

This course will focus on the electron transport in semiconductors, with emphasis on the mesoscopic systems. The aim is to understand the transport of electrons in low dimensional systems, where even particles with statistics different than fermions and bosons will be discussed.

PHYS-640: Neutron and X-ray Scattering of Quantum Materials

NNeutron and X-ray scattering are some of the most powerful and versatile experimental methods to study the structure and dynamics of materials on the atomic scale. This course covers basic theory, instrumentation and scientific applications of these experimental methods.

MICRO-422: Lasers: theory and modern applications

This course gives an introduction to Lasers by both considering fundamental principles and applications. Topics that are covered include the theory of lasers, laser resonators and laser dynamics. In addition to the basic concepts, a variety of interesting laser systems and applications are covered

High-dimensional optimization under nonconvex excluded volume constraints

Antonio Sclocchi

We consider high-dimensional random optimization problems where the dynamical variables are subjected to nonconvex excluded volume constraints. We focus on the case in which the cost function is a simple quadratic cost and the excluded volume constraints are modeled by a perceptron constraint satisfaction problem. We show that depending on the density of constraints, one can have different situations. If the number of constraints is small, one typically has a phase where the ground state of the cost function is unique and sits on the boundary of the island of configurations allowed by the constraints. In this case, there is a hypostatic number of marginally satisfied constraints. If the number of constraints is increased one enters a glassy phase where the cost function has many local minima sitting again on the boundary of the regions of allowed configurations. At the phase transition point, the total number of marginally satisfied constraints becomes equal to the number of degrees of freedom in the problem and therefore we say that these minima are isostatic. We conjecture that by increasing further the constraints the system stays isostatic up to the point where the volume of available phase space shrinks to zero. We derive our results using the replica method and we also analyze a dynamical algorithm, the Karush-Kuhn-Tucker algorithm, through dynamical mean-field theory and we show how to recover the results of the replica approach in the replica symmetric phase.

AMER PHYSICAL SOC2022

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The S-matrix Bootstrap Reloaded

Aditya Hebbar

Quantum field theories (QFTs) are the backbone upon which the edifice of modern physics is built. In this thesis we explore the S-matrix bootstrap which is a non-perturbative method that constrains the vast space of QFTs by using consistency conditions that they must satisfy. The thesis is divided into two parts.In part I of the thesis we study the S-matrix bootstrap for particles with spin in 4 spacetime dimensions and apply the formalism to scattering of identical Majorana fermions to estimate bounds on their quartic couplings and their cubic (Yukawa) coupling to scalar particles. In part II of the thesis, we consider the scattering of massless (Goldstone) excitations on a long flux tube. We use the S-matrix bootstrap to constrain Wilson coefficients of higher dimension operators in the low energy flux tube effective field theory. These constraints naturally translate to bounds on the ground state and excited state energy levels of long flux tubes. The techniques used in this thesis should be extendable to many other systems, both massive and massless. We conclude by discussing some of these possibilities.

EPFL2021

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Unconventional quantum ordered and disordered states in the highly frustrated spin-1/2 Ising-Heisenberg model on triangles-in-triangles lattices

Jana Cisárová

The spin-1/2 Ising-Heisenberg model on two geometrically related triangles-in-triangles lattices is exactly solved through the generalized star-triangle transformation, which establishes a rigorous mapping correspondence with the effective spin-1/2 Ising model on a triangular lattice. Basic thermodynamic quantities were exactly calculated within this rigorous mapping method along with the ground-state and finite-temperature phase diagrams. Apart from the classical ferromagnetic phase, both investigated models exhibit several unconventional quantum ordered and disordered ground states. A mutual competition between two ferromagnetic interactions of basically different character generically leads to the emergence of a quantum ferromagnetic phase, in which a symmetric quantum superposition of three up-up-down states of the Heisenberg trimers accompanies a perfect alignment of all Ising spins. In the highly frustrated regime, we have either found the disordered quantum paramagnetic phase with a substantial residual entropy or a similar but spontaneously ordered phase with a nontrivial criticality at finite temperatures. The latter quantum ground state exhibits a striking coexistence of imperfect spontaneous order with partial disorder, which is evidenced by a quantum reduction of the spontaneous magnetization of Heisenberg spins that indirectly causes a small reduction of the spontaneous magnetization of otherwise classical Ising spins. DOI: 10.1103/PhysRevB.87.024421

Amer Physical Soc2013

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