Portail HAL du Collège de France
Not a member yet
22122 research outputs found
Sort by
Floquet dynamical chiral spin liquid at finite frequency
No full textInternational audienceChiral Spin Liquids (CSL) are quantum spin analogs of electronic Fractional Chern Insulators. Their realizations on ultracold-atom or Rydberg-atom platforms remain very challenging. Recently, a setup of time-periodic modulations of nearest-neighbor Heisenberg couplings applied on an initial genuine spin liquid state on the square lattice has been proposed to stabilize a (Abelian) CSL phase. In the high-frequency limit, it was shown that time evolution can be described in terms of a static effective chiral Hamiltonian. Here we revisit this proposal and consider drives at lower frequency in a regime where the high-frequency Magnus expansion fails. We show that a Dynamical CSL (DCSL) is nevertheless stabilized in a finite range of frequency. The topological nature of this dynamical phase, as well as its instability below a critical frequency, is connected to specific features of the Floquet pseudo-energy spectrum. We also show that the DCSL can be represented faithfully by a two-dimensional time-periodic tensor network and, as in the static case, topological order is associated to a tensor gauge symmetry ( in that case)
Between the Lines: Editorial
No full textInternational audienceThe editorial committee is pleased to present volume 5 of the Journal of the European Association for Chinese Studies, which opens with a special section on “Commentary and Exegesis”.編委會榮幸地推出《歐洲漢學學會學刊》第五期。本期特設“註釋與詮釋”專題，作為開篇內容
The Galaxy Activity, Torus, and Outflow Survey (GATOS). V: Unveiling PAH survival and resilience in the circumnuclear regions of AGN with JWST
No full textInternational audienceWe analyze JWST MIRI/MRS observations of the infrared PAH bands in the nuclear and circumnuclear regions of local AGN from the GATOS Survey. In this work, we examine the PAH properties in the circumnuclear regions of AGN and AGN-outflows, and compare them to those in star-forming regions and the innermost regions of AGN. This study employs 4.9-28.1 micron sub-arcsecond angular resolution data to investigate the properties of PAH in three nearby sources (DL~30-40 Mpc). Our findings align with previous JWST studies, showing that the central regions of AGN show a larger fraction of neutral PAH molecules (i.e. elevated 11.3/6.2 and 11.3/7.7 PAH ratios) compared to star-forming galaxies. We find that the AGN might affect not only the PAH population in the innermost region but also in the extended regions up to ~kpc scales. By comparing our observations to PAH diagnostic diagrams, we find that, in general, regions located in the projected direction of the AGN-outflow occupy similar positions on the PAH diagnostic diagrams as those of the innermost regions of AGN. Star-forming regions that are not affected by the AGN in these galaxies share the same part of the diagram as Star-forming galaxies. We examine the potential of the PAH-H2 diagram to disentangle AGN versus star-forming activity. Our results suggest that in Sy-like AGN, illumination and feedback from the AGN might affect the PAH population at nuclear and kpc scales, in particular, the ionization state of the PAH grains. However, PAH sizes are rather similar. The carriers of the ionized PAH bands (6.2 and 7.7 micron) are less resilience than those of neutral PAH bands (11.3 micron), which might be particularly important for strongly AGN-host coupled systems. Therefore, caution must be applied when using PAH bands as star-formation rate indicators in these systems even at kpc scales, with the ionized ones being more affected by the AGN
Certification of non-Gaussian Einstein-Podolsky-Rosen Steering
No full textInternational audienceNon-Gaussian quantum states are a known necessary resource for reaching a quantum advantage and for violating Bell inequalities in continuous variable systems. As one kind of manifestation of quantum correlations, Einstein-Podolsky-Rosen (EPR) steering enables verification of shared entanglement even when one of the subsystems is not characterized. However, how to detect and classify such an effect for non-Gaussian states is far from being well understood. Here, we present an efficient non-Gaussian steering criterion based on the high-order observables and conduct a systematic investigation into the hierarchy of non-Gaussian steering criteria. Moreover, we apply our criterion to three experimentally-relevant non-Gaussian states under realistic conditions and, in particular, propose a feasible scheme to create multi-component cat states with tunable size by performing a suitable high-order quadrature measurement on the steering party. Our work reveals the fundamental characteristics of non-Gaussianity and quantum correlations, and offers new insights to explore their applications in quantum information processing
Encounters with the Invisible. Revisiting Spirit Possession in the Himalayas
No full textInternational audienceThis volume considers spirit possession in the Himalayas and the various ways in which invisible powers are made present. It does so by examining material representations of these powers through artefacts, animals, plants and natural substances, while also focusing on narratives of people’s encounters with the invisible that may help them to reconfigure reality. Through these two approaches, the contributions examine new phenomena associated with the concepts of "possession" and "shamanism", which otherwise tend to lead research into well-worn furrows. The book addresses a range of themes, including the gods of the Western Himalayas, death and ritual dissolution among Hyolmo Buddhists in Nepal, gods and rivers as legal persons in India, and the problem of conversion disorder in Nepal.Rich in ethnography, this book will be indispensable for scholars and researchers of anthropology, religion, spiritualism, sociology of religion, Himalayan studies, sociology and South Asia
Gaussian quantum metrology for mode-encoded parameters: general theory and imaging applications
No full textInternational audienceQuantum optical metrology aims to identify ultimate sensitivity bounds for the estimation of parameters econded into quantum states of the electromagnetic field. In many practical applications, including imaging, microscopy, and remote sensing, the parameter of interest is not only encoded in the quantum state of the field, but also in its spatio-temporal distribution, i.e. in its mode structure. In this mode-encoded parameter estimation setting, we derive an analytical expression for the quantum Fisher information valid for arbitrary multimode Gaussian fields. To illustrate the power of our approach, we apply our results to the estimation of the transverse separation between two point sources observed with a diffraction-limited imaging system. In this context, we determine the ultimate resolution provided by mutual coherence and squeezing of the sources
Loss features in ultracold <math><mmultiscripts><mi>Dy</mi><mprescripts/><none/><mn>162</mn></mmultiscripts></math> gases: Two- versus three-body processes
No full textInternational audienceDipolar gases like erbium and dysprosium have a dense spectrum of resonant loss features associated with their strong anisotropic interaction potential. These resonances display various behaviors with density and temperature, implying diverse microscopic properties. Here we quantitatively investigate the low-field (B<6G) loss features in ultracold thermal samples of Dy162. The atoms are spin polarized in their lowest internal state so that pure two-body losses due to spin relaxation are forbidden. However, our analysis reveals that some resonances lead to a two-body-like decay law, while others show the expected three-body decay. We present microscopic one-step and two-step models for these losses, investigate their temperature dependence, and detect a feature compatible with a d-wave Fano-Feshbach resonance that has not been observed before. We also report the variation of the scattering length around these resonances, inferred from the time-of-flight expansion of the condensate
Lecciones de la historia africana: Lección inaugural pronunciada en el Collège de France el jueves 3 de octubre de 2019
No full textInternational audienceSi nunca está de más señalar que las sociedades africanas están constituidas por el mismo tejido histórico que todas las demás sociedades, el pasado de África ha permanecido desconocido durante mucho tiempo. Ser historiador o arqueólogo especializado en África consiste tanto en desbrozar el pasado como captar su diversidad: la riqueza de la literatura oral y de la documentación escrita, la pluralidad de lenguas y religiones, la inventiva técnica y social, la cohabitación de formas políticas. Atento a las múltiples trayectorias históricas presentes, François-Xavier Fauvelle nos invita a escuchar lo que la historia de África tiene que enseñarnos
The Annual Difference: How a Four-Century Debate Between Confucian, Daoist, and Buddhist Thinkers on a Problem of Classical Exegesis Shaped a Predictive Mathematical Construct
No full textInternational audienceIn China, the precession of the equinoxes was conceptualized as an "annual difference" (suicha 歲差) between the tropical and sidereal year. The idea was introduced in the fourth century, it saw universal acceptance from the eighth century on, and it was in the four centuries in between that it was tried, debated, and spread whilst a Mediterranean-origin concept thereof arrived from India. Its four-century journey from fringe idea to universal truth is a well-studied point of interest in the history of astronomy. In this article, we will shift focus to the idea's polymathic protagonists and epistemic foundations to explore how a scientific idea was born, debated, transmitted, and taught in Confucian commentary and, no less important, how politics, geography, regional schools, foreign transmission, and the Buddhist and Daoist religions shaped how thinkers engaged with it as individuals and as communities. Inspired by the work of Chen Kanli and Randall Collins, the goal is to show that there is nothing simple or inexorable about how even an empirically useful tool of predictive astronomical modeling is received in the relevant expert community, as it is but one element in a complex network of people and ideas aligning and opposing in ever-evolving strategies to assert relevance