The Hydrogen Atom in Combined Electric and Magnetic Fields with Arbitrary Mutual Orientations

For the hydrogen atom in combined magnetic and electric fields we investigate the dependence of the quantum spectra, classical dynamics, and statistical distributions of energy levels on the mutual orientation of the two external fields. Resonance energies and oscillator strengths are obtained by exact diagonalization of the Hamiltonian in a complete basis set, even far above the ionization threshold. At high excitation energies around the Stark saddle point the eigenenergies exhibit strong level repulsions when the angle between the fields is varied. The large avoided crossings occur between states with the same approximately conserved principal quantum number, n, and this intramanifold mixing of states cannot be explained, not even qualitatively, by conventional perturbation theory. However, it is well reproduced by an extended perturbation theory which takes into account all couplings between the angular momentum and Runge-Lenz vector. The large avoided crossings are interpreted as a quantum manifestation of classical intramanifold chaos. This interpretation is supported by both classical Poincar\'e surfaces of section, which reveal a mixed regular-chaotic intramanifold dynamics, and the statistical analysis of nearest-neighbor-spacingComment: two-column version, 10 pages, REVTeX, 10 figures, uuencoded, submitted to Rhys. Rev.

Functional-renormalization-group approach to strongly coupled Bose-Fermi mixtures in two dimensions

We study theoretically the phase diagram of strongly coupled two-dimensional Bose-Fermi mixtures interacting with attractive short-range potentials as a function of the particle densities. We focus on the limit where the size of the bound state between a boson and a fermion is small compared to the average interboson separation and develop a functional-renormalization-group approach that accounts for the bound-state physics arising from the extended Fr\"{o}hlich Hamiltonian. By including three-body correlations we are able to reproduce the polaron-to-molecule transition in two-dimensional Fermi gases in the extreme limit of vanishing boson density. We predict frequency- and momentum-resolved spectral functions and study the impact of three-body correlations on quasiparticle properties. At finite boson density, we find that when the bound-state energy exceeds the Fermi energy by a critical value, the fermions and bosons can form a fermionic composite with a well-defined Fermi surface. These composites constitute a Fermi sea of dressed Feshbach molecules in the case of ultracold atoms while in the case of atomically thin semiconductors a trion liquid emerges. As the boson density is increased further, the effective energy gap of the composites decreases, leading to a transition into a strongly correlated phase where polarons are hybridized with molecular degrees of freedom. We highlight the universal connection between two-dimensional semiconductors and ultracold atoms and we discuss perspectives for further exploring the rich structure of strongly coupled Bose-Fermi mixtures in these complementary systems.Comment: 28 pages, 12 figure

Preprint arXiv: 2209.11758 Submitted on 23 Sep 2022

An impurity interacting with an ultracold Fermi gas can form either a polaron state or a dressed molecular state in which the impurity forms a bound state with one gas particle. This molecular state features rich physics, including a first-order transition to the polaron state and a negative effective mass at small interactions. However, these features have remained so far experimentally inaccessible. In this work we show theoretically how the molecular state can be directly prepared experimentally even in its excited state using state-of-the-art cold atom Raman spectroscopy techniques. Initializing the system in the ultra-strong coupling limit, where the binding energy of the molaron is much larger than the Fermi energy, our protocol maps out the momentum-dependent spectral function of the molecule. Using a diagrammatic approach we furthermore show that the molecular spectral function serves as a direct precursor of the elusive Fulde-Ferell-Larkin-Ovchinnikov phase, which is realized for a finite density of fermionic impurity particles. Our results pave the way to a systematic understanding of how composite particles form in quantum many-body environments and provide a basis to develop new schemes for the observation of exotic phases of quantum many-body systems

Preprint arXiv: 2211.12495 Submitted on 22 Nov 2022

We study induced pairing between two identical fermions mediated by anattractively interacting quantum impurity in two-dimensional systems. Based ona Stochastic Variational Method (SVM), we investigate the influence ofconfinement and finite interaction range effects on the mass ratio beyond whichthe ground state of the quantum three-body problem undergoes a transition froma composite bosonic trimer to an unbound dimer-fermion state. We find thatconfinement as well as a finite interaction range can greatly enhance trimerstability, bringing it within reach of experimental implementations such asfound in ultracold atom systems. In the context of solid-state physics oursolution of the confined three-body problem shows that exciton-mediatedinteractions can become so dominant that they can even overcome detrimentalCoulomb repulsion between electrons in atomically-thin semiconductors. Our workthus paves the way towards a universal understanding of boson-induced pairingacross various fermionic systems at finite density, and opens perspectivestowards realizing novel forms of electron pairing beyond the conventionalparadigm of Cooper pair formation

INSEMINAÇÃO ARTIFICIAL INTRAUTERINA E CERVICAL EM OVELHAS UTILIZANDO SÊMEN REFRIGERADO

O presente trabalho objetivou verificar a prenhez de ovelhas inseminadas por via intrauterina ou cervical com sêmen refrigerado a 5ºC durante 8 horas nos diluentes citrato-gema e Cornell University Extender (CUE). Foram utilizados 4 carneiros da raça Suffolk. Em cada inseminação era colhido sêmen de 2 animais e após a avaliação seminal as amostras eram homogeneizadas, divididas em 2 alíquotas e diluídas na proporção de uma parte de sêmen para três de diluente em citrato-gema e CUE. A diluição ocorria a 30ºC e o abaixamento progressivo da temperatura se dava em 2 horas em caixa de isopor contendo gelo. As amostras permaneceram nesta temperatura durante 8 horas. Foram inseminadas 91 ovelhas mestiças da raça Suffolk, as quais tiveram o estro sincronizado com pessários vaginais impregnados com 50 mg de acetato de medroxiprogesterona, permanecendo por 14 dias, quando se administrou 500 UI de Gonadotrofina Coriônica (eCG) via intramuscular. Todas as ovelhas foram inseminadas independente do aparecimento do estro. A aplicação do sêmen foi realizada pela via cervical e intra-uterina por laparoscopia. A dose mínima inseminante foi de 250 milhões de espermatozóides, em volume de 0,4 ml, por ovelha. A utilização do diluente CUE resultou em 69,56% (n=23) e 8,33% (n=24) de prenhez para as vias intra-uterina e cervical, respectivamente contra 85,71% (n=21) e 21,74% (n=23) para o diluente citrato-gema. O sêmen diluído em citrato-gema forneceu índices de prenhez superiores, porém não significativos (P>0,05), nas duas vias estudadas em relação ao CUE. A fertilidade foi superior quando se utilizou a via intra-uterina (P0.05) has been found between values of pregnancy attained with suspensions of spermatozoa either in CUE or in citrate-york extender, in spite of the fact that the latter one gave higher pregnancy rates. Intrauterine insemination gave higher values of fertility (

Quantum Arnol'd Diffusion in a Simple Nonlinear System

We study the fingerprint of the Arnol'd diffusion in a quantum system of two coupled nonlinear oscillators with a two-frequency external force. In the classical description, this peculiar diffusion is due to the onset of a weak chaos in a narrow stochastic layer near the separatrix of the coupling resonance. We have found that global dependence of the quantum diffusion coefficient on model parameters mimics, to some extent, the classical data. However, the quantum diffusion happens to be slower that the classical one. Another result is the dynamical localization that leads to a saturation of the diffusion after some characteristic time. We show that this effect has the same nature as for the studied earlier dynamical localization in the presence of global chaos. The quantum Arnol'd diffusion represents a new type of quantum dynamics and can be observed, for example, in 2D semiconductor structures (quantum billiards) perturbed by time-periodic external fields.Comment: RevTex, 11 pages including 12 ps-figure

Manifestation of the Arnol'd Diffusion in Quantum Systems

We study an analog of the classical Arnol'd diffusion in a quantum system of two coupled non-linear oscillators one of which is governed by an external periodic force with two frequencies. In the classical model this very weak diffusion happens in a narrow stochastic layer along the coupling resonance, and leads to an increase of total energy of the system. We show that the quantum dynamics of wave packets mimics, up to some extent, global properties of the classical Arnol'd diffusion. This specific diffusion represents a new type of quantum dynamics, and may be observed, for example, in 2D semiconductor structures (quantum billiards) perturbed by time-periodic external fields.Comment: RevTex, 4 pages including 7 ps-figures, corrected forma