Matière dégénérée | EPFL Graph Search

On dit de la matière qu'elle est dégénérée lorsque sa densité est suffisamment élevée pour que le principe d'exclusion de Pauli intervienne à l'échelle macroscopique, ce qui a pour conséquence de modifier la relation qui lie normalement la pression et le volume d'un gaz avec sa température. À partir d'une certaine pression (ou d'une certaine densité), la matière est déstructurée et se comporte comme un gaz. Elle subit alors une force, exercée par ses électrons, qui s'oppose à sa contraction et empêche sa densité d'augmenter, la pression de dégénérescence. Cet état de la matière se rencontre à l'état naturel dans les étoiles, plus particulièrement dans les étoiles en fin de vie que sont les naines blanches et les étoiles à neutrons. On rencontre aussi la matière dégénérée dans l'hydrogène métallique. Principe général Le principe d'exclusion de Pauli interdit à deux électrons d'être dans le même état quantique, dont les deux variables sont le spin, de valeur +½ ou -½, et

Leptogenesis from first principles in the resonant regime

The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results. (c) 2012 Elsevier Inc. All rights reserved.

Academic Press Inc Elsevier Science2013

Viability of Dirac phase leptogenesis

Steve Blanchet

We discuss the conditions for a non-vanishing Dirac phase delta and mixing angle theta(13), sources of CP violation in neutrino oscillations, to be uniquely responsible for the observed matter - antimatter asymmetry of the Universe through leptogenesis. We show that this scenario, that we call delta-leptogenesis, is viable when the degenerate limit for the heavy right-handed (RH) neutrino spectrum is considered. We derive an interesting joint condition on sin theta(13) and the absolute neutrino mass scale that can be tested in future neutrino oscillation experiments. In the limit of the hierarchical heavy RH neutrino spectrum, we strengthen the previous result that delta-leptogenesis is only very marginally allowed, even when the production from the two heavier RH neutrinos is taken into account. An improved experimental upper bound on sin theta(13) and/or an account of quantum kinetic effects could completely rule out this option in the future. Therefore, delta-leptogenesis can be also regarded as motivation for models with degenerate heavy neutrino spectrum.

2008

Cavity Quantum Electrodynamics with strongly correlated fermions

Kevin Etienne Robert Roux

This thesis presents the first cavity quantum electrodynamics experiments performed with a degenerate gas of

^6

Li with strong atom-atom interactions. The first part of this manuscript describes the design and the building of the apparatus that has been especially developed to bring together a high-finesse optical cavity and a strongly interacting Fermi gas. I described how the cavity and all the laser-cooling procedure can be realized in the same vacuum chamber, thus speeding up the production cycle of the degenerate Fermi gas.This new experimental apparatus is the first of its kind combining these two field of quantum physics. Placing a quantum gas of Fermions within an optical resonator gives a important technical advantages, allowing for the fast, all-optical production of a degenerate gas of

^6

Li. We apply an technique that make it possible to modify the longitudinal structure of the cavity trap to cancel its lattice structure. It increases the phase space density after the evaporative cooling leading to a ultracold gas at temperature lower than ten percent of the Fermi temperature. We describe how magnetic field allows us to tune the interatomic interactions, making use of the broad Feshbach resonance of

^6

Li at

832

G and how we characterize the thermodynamic properties of the ultracold Fermi gas. The direct observation of phase separation for a spin-imbalanced Fermi gas between a fully paired region at the cloud center, surrounded by a spin-polarized shell experimentally proves the apparition of superfluidity at low enough temperature.The first experiment showing the strong coupling between the cavity photons and the strongly interacting Fermi gas is shown in this manuscript. The observation of large avoided-crossings when performing cavity transmission spectroscopy experiment are the experimental smoking gun of the strong light-matter coupling regime. We observe the expected scaling of the light-matter coupling strength with the number of atoms in the gas, proving the coherent coupling of the atoms with the cavity field.The thirs part of this manuscript presents the first cavity quantum electrodynamics experiment where a pairs of atoms couple to the cavity photons, forming a new dressed state: the pair-polariton. This dressed state inherits from its atomic part the characteristics of the many-body physics of the strongly interacting Fermi gas. We confirm experimentally that the properties of the short-range two-body correlation function, know as Tan's contact, can directly be measured optically, on the pair-polariton transmission spectrum. We observe the coherent coupling of the ground state Fermion pairs with the cavity photons and use the pair-polariton to perform single shot, real-time, weakly destructive measurement of the short range two body correlation function. This new measurement of Tan's contact allows to follow in-time the evolution of a single system, contrasting with existing techniques.The last part of this thesis will show experiment carried far in the dispersive regime, where both the cavity resonance and the probe laser frequency are far detuned from the atomic resonance. We will discuss how we can, in this regime, measure the atom number evolution in-time, with a weak destructivity. We show that optical non-linearity emerges and depends on the atom-atom interaction strength. Last we implement a pump not aligned with the cavity axis that allows to create long-range interactions between atoms.

EPFL2022

Cavity Quantum Electrodynamics with strongly correlated fermions

Kevin Etienne Robert Roux

This thesis presents the first cavity quantum electrodynamics experiments performed with a degenerate gas of

^6

^6

^6

Li at

832

EPFL2022