Strongly correlated Fermions strongly coupled to light

Strong quantum correlations in matter are responsible for some of the most extraordinary properties of material, from magnetism to high-temperature superconductivity, but their integration in quantum devices requires a strong, coherent coupling with photons, which still represents a formidable technical challenge in solid state systems. In cavity quantum electrodynamics, quantum gases such as Bose-Einstein condensates or lattice gases have been strongly coupled with light. However, neither Fermionic quantum matter, comparable to electrons in solids, nor atomic systems with controlled interactions, have thus far been strongly coupled with photons. Here we report on the strong coupling of a quantum-degenerate unitary Fermi gas with light in a high finesse cavity. We map out the spectrum of the coupled system and observe well resolved dressed states, resulting from the strong coupling of cavity photons with each spin component of the gas. We investigate spin-balanced and spin-polarized gases and find quantitative agreement with ab-initio calculation describing light-matter interaction. Our system offers complete and simultaneous control of atom-atom and atom-photon interactions in the quantum degenerate regime, opening a wide range of perspectives for quantum simulation.Comment: Updated reference

Density-wave ordering in a unitary Fermi gas with photon-mediated interactions

A density wave (DW) is a fundamental type of long-range order in quantum matter tied to self-organization into a crystalline structure. The interplay of DW order with superfluidity can lead to complex scenarios that pose a great challenge to theoretical analysis. In the last decades, tunable quantum Fermi gases have served as model systems for exploring the physics of strongly interacting fermions, including most notably magnetic ordering, pairing and superfluidity, and the crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to a Bose-Einstein condensate (BEC). Here, we realize a Fermi gas featuring both strong, tunable contact interactions and photon-mediated, spatially structured long-range interactions in a transversely driven high-finesse optical cavity. Above a critical long-range interaction strength DW order is stabilized in the system, which we identify via its superradiant light scattering properties. We quantitatively measure the variation of the onset of DW order as the contact interaction is varied across the BCS-BEC crossover, in qualitative agreement with a mean-field theory. The atomic DW susceptibility varies over an order of magnitude upon tuning the strength and the sign of the long-range interactions below the self-ordering threshold, demonstrating independent and simultaneous control over the contact and long-range interactions. Therefore, our experimental setup provides a fully tunable and microscopically controllable platform for the experimental study of the interplay of superfluidity and DW order.Comment: 11 pages, 7 figure

Incidência e Estudo Morfológico de Pontes Miocárdicas no Estado do Ceará: Um Estudo Cadavérico

Resumo Fundamento As pontes miocárdicas (PM) são anomalias anatômicas com possíveis repercussões clínicas, e, portanto, seu entendimento merece atenção. Objetivo Para determinar a prevalência e caracterizar a PM em corações humanos do estado do Ceará. Métodos: Foram usados cinquenta corações de cadáveres humanos adultos da Faculdade de Medicina da Universidade Federal do Ceará, Brasil. Os corações foram dissecados para identificar PMs que passam sobre parte da artéria coronária. O segmento da artéria (proximal, médio e distal) com a ponte foi identificado. O diâmetro externo da artéria nos pontos proximal e distal da PM foi medido. O comprimento e a espessura da PM também foram medidos com um calibre eletrônico. O índice de massa muscular (IMM) da PM foi calculado como o produto do comprimento pela espessura expresso em milímetros. O nível de significância adotado para a análise estatística foi 5%. Resultados A PM foi confirmada em 40% da amostra. Aproximadamente um terço da amostra tinha apenas 1 PM. A PM foi encontrada mais frequentemente sobre o ramo interventricular anterior da artéria coronária esquerda (59,25%, p = 0,02), e sua prevalência em outros ramos foi muito mais baixa (22,23%). Os segmentos das artérias mais afetados foram o superior (44,44%) e o médio (40,74%). O diâmetro médio das artérias proximais em relação à PM foi de 2,38 ± 0,97 mm (intervalo = 0,78 - 5,15 mm), e o diâmetro distal da PM foi de 1,71 ± 0,75 mm (intervalo = 0,42 - 3,58 mm). O comprimento foi medido como média = 8,55 ± 5,27 mm, e a espessura média foi de 0,89 ± 0,33 mm. Conclusão A alta prevalência de PM tem mais probabilidade de afetar o sistema da artéria coronária esquerda com IMM maior do que outros ramos afetados

Fraqueza muscular adquirida na UTI (ICU-AW): efeitos sistêmicos da eletroestimulação neuromuscular

Com os avanços tecnológicos alcançados atualmente na terapia intensiva e maior sobrevida dos pacientes, outros desafios têm surgido para os profissionais de saúde. Dentre alguns, destaca-se a fraqueza muscular adquirida na UTI (ICU-AW), caracterizada por paresia esquelética e respiratória dos músculos promovendo aumento nastaxas de mortalidade e comprometimento da qualidade de vida. Sua incidência varia de 30% a 60% e tem na síndrome da resposta inflamatória sistêmica (SIRS) e na disfunção de múltiplos órgãos (DMO) sua principal etiologia. Outros fatores de risco como a hiperglicemia,o uso de bloqueadores neuromusculares e sedativos, a imobilidade e a própria ventilação mecânica estão entre os mais comuns. Entre as medidas de combate à ICU-AW, está o conceito de mobilização precoce, bem como despertar diário e controle estreito da glicemia. Nesse contexto, a eletroestimulação muscular apresenta-se como recurso de grande valia. Sua principal vantagem está no fato de poder ser empreendida independentemente da cooperação do paciente, epor ser capaz de gerar respostas musculares eficientes, bem como resultados satisfatórios na preservação da massa muscular, condicionamento físico e funcionalidade dos que usam essa ferramenta. Desfechos interessantes têm sido observados em diversos perfis de pacientes, como os de doença pulmonar obstrutiva crônica (DPOC)e traumatismo raquimedular (TRM). No paciente crítico, seu uso tem mostrado redução nos tempos de ventilação mecânica (VM), internação na UTI e maior funcionalidade dos pacientes. A relevância dos efeitos sistêmicos e metabólicos provenientes da eletroestimulação neuromuscular (ENM) tem sido a base para os estudos nos pacientes críticos. Portanto, a ICU-AW é uma realidade no cenário da terapia intensiva e sua prevenção tem dado margem à aparição de novas propostas e ferramentas na prevenção dessas complicações

Many-body physics with strongly interacting fermions coupled to light

This thesis reports on the realization of the first experiments conducted with superfluid, strongly interacting Fermi gases of 6Li coupled to the light field of an optical cavity. In the scope of existing ultracold atomic platforms, this is the first time that a system with strong ground state fermionic correlations is operated in the framework of cavity quantum electrodynamics (cQED). From a condensed matter perspective, the system features a fully controllable microscopic Hamiltonian with control over both the strength of the ground state and light-matter interactions and the geometry of the latter. This contrasts with usual solid-state systems, in which the properties of the ground states are hardly tunable. As such our experiment is the perfect platform to simulate the physics of strongly correlated matter coupled to light fields. The manuscript is divided in three parts. The first part is dedicated to the presentation of technical details of the experiment and of measurement techniques we routinely employ to create and probe our strongly interacting gases coupled to light. We introduce the use of the cavity as a probing tool by presenting the achievement of strong light-matter coupling between the atomic ensemble and the cavity field. Similarly, we present a robust thermometry technique for the unitary Fermi gas, with which we measure temperature of the gases deep in the superfluid, quantum degenerate regime. In a second part we focus on the measurements of the strong atom-atom correlations which emerge from the energy spectrum of the atoms-cavity system. We start by laying down the theoretical basis needed for the understanding of the origin of the strong atom-atom interaction, and present its consequence on the many-body wavefunction of the gas by introducing the two-body contact as a universal thermodynamic quantity. We then report on the observation of strong light-matter coupling between pairs of atoms and the cavity field via photoassociation transitions. We describe the resulting light-matter coupling strength in terms of the two-body contact, imprinting many-body correlations onto cavity spectra for the first time. In the following experiment we study the optomechanical response of the gas in the dispersive regime. We observe distorted cavity transmission profiles, signatures of the nonlinear Kerr effect. The strength of the nonlinearity is governed by the density response of the gas, which we express via an operator product expansion in terms of the contact. In the last part, we investigate the effects of engineering long-range, photon-mediated interactions in the gas. We formally show how the system is expected, above a critical value for the strength of the long-range interaction, to undergo a phase transition to a density ordered state. The onset of density-ordering is observed by the superradiant properties of the ordered phase, and we show that it is also controlled by the density response of the unperturbed gas. In addition, we measure the divergence of the density wave susceptibility as the strength of the long-range interactions approaches the critical points: a striking feature of phase transitions. By measuring its temperature after the experiment, we prove that the gas remains superfluid.LQ

Universal pair polaritons in a strongly interacting Fermi gas

Cavity quantum electrodynamics (QED) manipulates the coupling of light with matter, and allows several emitters to couple coherently with one light mode1. However, even in a many-body system, the light–matter coupling mechanism has so far been restricted to one-body processes. Leveraging cavity QED for the quantum simulation of complex, many-body systems has thus far relied on multi-photon processes, scaling down the light–matter interaction to the low energy and slow time scales of the many-body problem. Here we report cavity QED experiments using molecular transitions in a strongly interacting Fermi gas, directly coupling cavity photons to pairs of atoms. The interplay of strong light–matter and strong interparticle interactions leads to well-resolved pair polaritons—hybrid excitations coherently mixing photons, atom pairs and molecules. The dependence of the pair-polariton spectrum on interatomic interactions is universal, independent of the transition used, demonstrating a direct mapping between pair correlations in the ground state and the optical spectrum. This represents a magnification of many-body effects by two orders of magnitude in energy. In the dispersive regime, it enables fast, minimally destructive measurements of pair correlations, and opens the way to their measurement at the quantum limit and their coherent manipulation using dynamical, quantized optical fields.LQ

Compact bulk-machined electromagnets for quantum gas experiments

We present an electromagnet combining a large number of windings in a constrained volume with efficient cooling. It is based on bulk copper where a small pitch spiral is cut out and impregnated with epoxy, forming an ensemble which is then machined at will to maximize the use of the available volume. Water cooling is achieved in parallel by direct contact between coolant and the copper windings. A pair of such coils produces magnetic fields suitable for exploiting the broad Feshbach resonance of $^6$Li at 832.2 G. It offers a compact and cost-effective solution for quantum gas experiments

Compact bulk-machined electromagnets for quantum gas experiments

We present an electromagnet combining a large number of windings in a constrained volume with efficient cooling. It is based on bulk copper where a small pitch spiral is cut out and impregnated with epoxy, forming an ensemble which is then machined at will to maximize the use of the available volume. Water cooling is achieved in parallel by direct contact between coolant and the copper windings. A pair of such coils produces magnetic fields suitable for exploiting the broad Feshbach resonance of Li-6 at 832.2 G. It offers a compact and cost-effective alternative solution for quantum gas experiments

Optomechanical Response of a Strongly Interacting Fermi Gas

We study a Fermi gas with strong, tunable interactions dispersively coupled to a high-finesse cavity. Upon probing the system along the cavity axis, we observe a strong optomechanical Kerr nonlinearity originating from the density response of the gas to the intracavity field and measure it as a function of interaction strength. We find that the zero-frequency density response function of the Fermi gas increases by a factor of two from the Bardeen-Cooper-Schrieffer to the Bose-Einstein condensate regime. The results are in quantitative agreement with a theory based on operator-product expansion, expressing the density response in terms of universal functions of the interactions, the contact and the internal energy of the gas. This provides an example of a driven-dissipative, strongly correlated system with a strong nonlinear response, opening up perspectives for the sensing of weak perturbations or inducing long-range interactions in Fermi gases