Measurement of the superfluid fraction of a supersolid by Josephson effect.

A new class of superfluids and superconductors with spatially periodic modulation of the superfluid density is arising1-12. It might be related to the supersolid phase of matter, in which the spontaneous breaking of gauge and translational symmetries leads to a spatially modulated macroscopic wavefunction13-16. This relation was recognized only in some cases1,2,5-9 and there is the need for a universal property quantifying the differences between supersolids and ordinary matter, such as the superfluid fraction, which measures the reduction in superfluid stiffness resulting from the spatial modulation16-18. The superfluid fraction was introduced long ago16, but it has not yet been assessed experimentally. Here we demonstrate an innovative method to measure the superfluid fraction based on the Josephson effect, a ubiquitous phenomenon associated with the presence of a physical barrier between two superfluids or superconductors19, which might also be expected for supersolids20, owing to the spatial modulation. We demonstrate that individual cells of a supersolid can sustain Josephson oscillations and we show that, from the current-phase dynamics, we can derive directly the superfluid fraction. Our study of a cold-atom dipolar supersolid7 reveals a relatively large sub-unity superfluid fraction that makes realistic the study of previously unknown phenomena such as partially quantized vortices and supercurrents16-18. Our results open a new direction of research that may unify the description of all supersolid-like systems.

Spatial Bloch Oscillations of a Quantum Gas in a "Beat-Note" Superlattice.

We report the experimental realization of a new kind of optical lattice for ultracold atoms where arbitrarily large separation between the sites can be achieved without renouncing to the stability of ordinary lattices. Two collinear lasers, with slightly different commensurate wavelengths and retroreflected on a mirror, generate a superlattice potential with a periodic "beat-note" profile where the regions with large amplitude modulation provide the effective potential minima for the atoms. To prove the analogy with a standard large spacing optical lattice we study Bloch oscillations of a Bose Einstein condensate with negligible interactions in the presence of a small force. The observed dynamics between sites separated by ten microns for times exceeding one second proves the high stability of the potential. This novel lattice is the ideal candidate for the coherent manipulation of atomic samples at large spatial separations and might find direct application in atom-based technologies like trapped-atom interferometers and quantum simulators.

Evidence of superfluidity in a dipolar supersolid from nonclassical rotational inertia.

A key manifestation of superfluidity in liquids and gases is a reduction of the moment of inertia under slow rotations. Nonclassical rotational effects have also been considered in the context of the elusive supersolid phase of matter, in which superfluidity coexists with a lattice structure. Here, we show that the recently discovered supersolid phase in dipolar quantum gases features a reduced moment of inertia. Using a dipolar gas of dysprosium atoms, we studied a peculiar rotational oscillation mode in a harmonic potential, the scissors mode, previously investigated in ordinary superfluids. From the measured moment of inertia, we deduced a superfluid fraction that is different from zero and of order of unity, providing direct evidence of the superfluid nature of the dipolar supersolid.

Supersolid symmetry breaking from compressional oscillations in a dipolar quantum gas.

Supersolids are exotic materials combining the frictionless flow of a superfluid with the crystal-like periodic density modulation of a solid. The supersolid phase of matter was predicted 50 years ago1-3 for solid helium4-8. Ultracold quantum gases have recently been made to exhibit periodic order typical of a crystal, owing to various types of controllable interaction9-13. A crucial feature of a D-dimensional supersolid is the occurrence of D + 1 gapless excitations, reflecting the Goldstone modes associated with the spontaneous breaking of two continuous symmetries: the breaking of phase invariance, corresponding to the locking of the phase of the atomic wave functions at the origin of superfluid phenomena, and the breaking of translational invariance due to the lattice structure of the system. Such modes have been the object of intense theoretical investigations1,14-18, but they have not yet been observed experimentally. Here we demonstrate supersolid symmetry breaking through the appearance of two distinct compressional oscillation modes in a harmonically trapped dipolar Bose-Einstein condensate, reflecting the gapless Goldstone excitations of the homogeneous system. We observe that the higher-frequency mode is associated with an oscillation of the periodicity of the emergent lattice and the lower-frequency mode characterizes the superfluid oscillations. This work also suggests the presence of two separate quantum phase transitions between the superfluid, supersolid and solid-like configurations.

Observation of a Dipolar Quantum Gas with Metastable Supersolid Properties.

The competition of dipole-dipole and contact interactions leads to exciting new physics in dipolar gases, well illustrated by the recent observation of quantum droplets and rotons in dipolar condensates. We show that the combination of the roton instability and quantum stabilization leads under proper conditions to a novel regime that presents supersolid properties due to the coexistence of stripe modulation and phase coherence. In a combined experimental and theoretical analysis, we determine the parameter regime for the formation of coherent stripes, whose lifetime of a few tens of milliseconds is limited by the eventual destruction of the stripe pattern due to three-body losses. Our results open intriguing prospects for the development of long-lived dipolar supersolids.

Self-Bound Quantum Droplets of Atomic Mixtures in Free Space.

Self-bound quantum droplets are a newly discovered phase in the context of ultracold atoms. In this Letter, we report their experimental realization following the original proposal by Petrov [Phys. Rev. Lett. 115, 155302 (2015)PRLTAO0031-900710.1103/PhysRevLett.115.155302], using an attractive bosonic mixture. In this system, spherical droplets form due to the balance of competing attractive and repulsive forces, provided by the mean-field energy close to the collapse threshold and the first-order correction due to quantum fluctuations. Thanks to an optical levitating potential with negligible residual confinement, we observe self-bound droplets in free space, and we characterize the conditions for their formation as well as their size and composition. This work sets the stage for future studies on quantum droplets, from the measurement of their peculiar excitation spectrum to the exploration of their superfluid nature.

Quantum phase slips: from condensed matter to ultracold quantum gases.

Quantum phase slips (QPS) are the primary excitations in one-dimensional superfluids and superconductors at low temperatures. They have been well characterized in most condensed-matter systems, and signatures of their existence have been recently observed in superfluids based on quantum gases too. In this review, we briefly summarize the main results obtained on the investigation of phase slips from superconductors to quantum gases. In particular, we focus our attention on recent experimental results of the dissipation in one-dimensional Bose superfluids flowing along a shallow periodic potential, which show signatures of QPS.This article is part of the themed issue 'Breakdown of ergodicity in quantum systems: from solids to synthetic matter'.

Crossing Over from Attractive to Repulsive Interactions in a Tunneling Bosonic Josephson Junction.

We explore the interplay between tunneling and interatomic interactions in the dynamics of a bosonic Josephson junction. We tune the scattering length of an atomic ^{39}K Bose-Einstein condensate confined in a double-well trap to investigate regimes inaccessible to other superconducting or superfluid systems. In the limit of small-amplitude oscillations, we study the transition from Rabi to plasma oscillations by crossing over from attractive to repulsive interatomic interactions. We observe a critical slowing down in the oscillation frequency by increasing the strength of an attractive interaction up to the point of a quantum phase transition. With sufficiently large initial oscillation amplitude and repulsive interactions, the system enters the macroscopic quantum self-trapping regime, where we observe coherent undamped oscillations with a self-sustained average imbalance of the relative well population. The exquisite agreement between theory and experiments enables the observation of a broad range of many body coherent dynamical regimes driven by tunable tunneling energy, interactions and external forces, with applications spanning from atomtronics to quantum metrology.

Quantum Phase Transitions with Parity-Symmetry Breaking and Hysteresis.

Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models1-3. Its observation in real systems is often hampered by finite temperatures and limited control of the system parameters. In this work we report for the first time the experimental observation of the full quantum phase diagram across a transition where the spatial parity symmetry is broken. Our system is made of an ultra-cold gas with tunable attractive interactions trapped in a spatially symmetric double-well potential. At a critical value of the interaction strength, we observe a continuous quantum phase transition where the gas spontaneously localizes in one well or the other, thus breaking the underlying symmetry of the system. Furthermore, we show the robustness of the asymmetric state against controlled energy mismatch between the two wells. This is the result of hysteresis associated with an additional discontinuous quantum phase transition that we fully characterize. Our results pave the way to the study of quantum critical phenomena at finite temperature4, the investigation of macroscopic quantum tunneling of the order parameter in the hysteretic regime and the production of strongly quantum entangled states at critical points5.

Can lateral semicircular canal dysplasia play a role in the genesis of hyperacusis.

Hyperacusis can be a prominent and disabling symptom of superior semicircular canal dehiscence associated with autophony and the Tullio phenomenon. We report three clinical cases characterized by disabling hyperacusis in which semicircular canals dehiscence was excluded by temporal bone high-resolution computed tomography. The images disclosed lateral semicircular canal dysplasia, characterized by a small bony island, and dilatation of both the anterior and the posterior arms of the lateral semicircular canal. Cochleo-vestibular examinations (pure tone audiometry, infra-red videonystagmoscopy, vibration-induced nystagmus test, vestibular evoked myogenic potentials) will also be described. To verify the transtympanic ventilation tube effect, bilateral myringotomies tubes were performed in one patient but no long lasting subjective benefit was noted. Concerning the pathophysiology of this condition, we hypothesized that the increased volume of inner ear liquid can modify the micromechanical function of the cochlea and the labyrinthine hydrodynamics. In conclusion, in the case of specific symptoms, such as hyperacusis, it is important to consider the possibility of an inner ear morphological alteration involving the lateral canal and vestibule structures, as well as the existence of bony semicircular canal dehiscence.

Tympanometric findings in superior semicircular canal dehiscence syndrome.

The diagnostic role of audio-impedancemetry in superior semicircular canal dehiscence (SSCD) disease is well known. In particular, since the first reports, the presence of evoked acoustic reflexes has represented a determining instrumental exhibit in differential diagnosis with other middle ear pathologies that are responsible for a mild-low frequencies air-bone gap (ABG). Even though high resolution computed tomography (HRCT) completed by parasagittal reformatted images still represents the diagnostic gold standard, several instrumental tests can support a suspect of labyrinthine capsule dehiscence when "suggestive" symptoms occur. Objective and subjective audiometry often represents the starting point of the diagnostic course aimed at investigating the cause responsible for the so-called "intra-labyrinthine conductive hearing loss". The purpose of this study is to evaluate the role of tympanometry, in particular of the inter-aural asymmetry ratio in peak compliance as a function of different mild-low frequencies ABG on the affected side, in the diagnostic work-up in patients with unilateral SSCD. The working hypothesis is that an increase in admittance of the "inner-middle ear" conduction system due to a "third mobile window" could be detected by tympanometry. A retrospective review of the clinical records of 45 patients with unilateral dehiscence selected from a pool of 140 subjects diagnosed with SSCD at our institution from 2003 to 2011 was performed. Values of ABG amplitude on the dehiscent side and tympanometric measurements of both ears were collected for each patient in the study group (n = 45). An asymmetry between tympanometric peak compliance of the involved side and that of the contralateral side was investigated by calculating the inter-aural difference and the asymmetry ratio of compliance at the eardrum. A statistically significant correlation (p = 0.015 by Fisher's test) between an asymmetry ratio ≥ 14% in favour of the pathologic ear and an ABG > 20 dB nHL on the same side was found. When "evocative" symptoms of SSCD associated with important ABG occur, the inter-aural difference in tympanometric peak compliance at the eardrum in favour of the "suspected" side could suggest an intra-labyrinthine origin for the asymmetry. Tympanometry would thus prove to be a useful instrument in clinical-instrumental diagnosis of SSCD in detection of cases associated with alterations of inner ear impedance.

Modeling the transport of interacting matter waves in a disordered system by a nonlinear diffusion equation.

We model the expansion of an interacting atomic Bose-Einstein condensate in a disordered lattice with a nonlinear diffusion equation normally used for a variety of classical systems. We find approximate solutions of the diffusion equation that well reproduce the experimental observations for both short and asymptotic expansion times. Our study establishes a connection between the peculiar shape of the expanding density profiles and the microscopic nonlinear diffusion coefficients.

Observation of subdiffusion in a disordered interacting system.

We study the transport dynamics of matter-waves in the presence of disorder and nonlinearity. An atomic Bose-Einstein condensate that is localized in a quasiperiodic lattice in the absence of atom-atom interaction shows instead a slow expansion with a subdiffusive behavior when a controlled repulsive interaction is added. The measured features of the subdiffusion are compared to numerical simulations and a heuristic model. The observations confirm the nature of subdiffusion as interaction-assisted hopping between localized states and highlight a role of the spatial correlation of the disorder.

Otoscopic findings in hypercholesterolemic subjects.

OBJECTIVES: We aimed to verify the extent of a previously cited relationship between tympanosclerosis and atherosclerosis by investigating subjects with dysfunction in lipid metabolism but no clinically apparent symptoms of atherosclerotic disease. METHODOLOGY: Forty hypercholesterolemic patients were submitted to Doppler ultrasound examination of carotid and vertebrobasilar arterial regions; results were matched to otoscopic findings. Otoscopy was performed to evaluate for sclerotic plaques of the tympanic membrane, which represent the most common, clinically non-relevant manifestation of tympanosclerosis. A control group of 41 randomly chosen healthy subjects were also included. RESULTS: Nine (22.5%) of 40 subjects with hypercholesterolemia showed tympanic sclerotic plaques at otoscopy compared to 2 (4.9%) out of 41 control patients. This difference was statistically significant (p = 0.02). An even stronger association (p = 0.01) was found between tympanic and arterial plaques in the study group, as we identified tympanic sclerotic plaques in 7 (41.2%) out of 17 patients with positive Doppler ultrasound signals for arterial plaques. Only two (8.7%) out of 23 subjects without plaques on Doppler ultrasound examination had tympanic sclerotic plaques. CONCLUSIONS: The results of this study confirm the existence of a link between tympanosclerosis and atherosclerosis. To our knowledge, this is the first report of a link between these findings in preclinical atherosclerotic conditions.

Meniere's disease: update of etiopathogenetic theories and proposal of a possible model of explanation.

Meniere's Disease (MD) is an affection consisting of an association of sensorineural hearing loss, tinnitus and vertigo initially presenting by crises. A review of the most considered possible causative factors and pathophysiologic interpretations allows us to underline the uncertainties which still exist about the genesis of this illness. We propose a mechanistic model based on the effect of a haemodynamic imbalance leading to transient ischaemia which could have an effect on the pH of the inner ear as well as on the work of the inner ear proton pumps. It is hypothesized that under ischaemic conditions and consequent metabolic acidity a preserved proton pump activity can generate an overload of anions in the endolymphatic partition, which is a closed system, thus resulting in an enhancement of osmolarity and consequently in the formation of a hydrops resulting in the development of fluctuating hearing loss, tinnitus and vertigo which characterize Meniere's Disease.

Langerhans cell histiocytosis: bilateral temporal bone involvement in an adult with diabetes insipidus.

OBJECTIVE: To present a clinical case of an adult affected by Langerhans cell histiocytosis with bilateral, non-simultaneous, involvement of the temporal bone, associated with diabetes insipidus and to review the literature. METHODOLOGY: A rare case of bilateral temporal bone involvement of Langerhans cell histiocytosis in a 42-year-old woman affected by diabetes insipidus is reported. We present patient's clinical history supported by radiologic, histopathologic and audiologic findings. RESULTS: The patient was submitted to a series of otologic surgical procedures due to the progression of the disease. Ossicular chain was always preserved, so that conservative surgery (canal wall-up technique) was performed, permitting the achievement of good hearing results, bilaterally. CONCLUSIONS: Temporal bone involvement of Langerhans cell histiocytosis may lead to a progressive chronic disease. However, the ossicular chain can remain uninvolved, making a conservative surgical treatment possible. Careful follow-up is essential for detecting new lesions and serial CT scans are mandatory.

Magnetic dipolar interaction in a Bose-Einstein condensate atomic interferometer.

We study the role played by the magnetic dipole interaction in the decoherence of a lattice-based interferometer that employs an alkali Bose-Einstein condensate with a tunable scattering length. The different behavior we observe for two different orientations of the dipoles gives us evidence of the anisotropic character of the interaction. The experiment is correctly reproduced by a model we develop only if the long-range interaction between different lattice sites is taken into account. Our model indicates that dipolar interaction can be compensated by a proper choice of the scattering length and that the magnetic dipole interaction should not represent an obstacle for atom interferometry with Bose-Einstein condensates with a tunable interaction.

Atom interferometry with a weakly interacting Bose-Einstein condensate.

We demonstrate the operation of an atom interferometer based on a weakly interacting Bose-Einstein condensate. We strongly reduce the interaction induced decoherence that usually limits interferometers based on trapped condensates by tuning the s-wave scattering length almost to zero via a magnetic Feshbach resonance. We employ a 39K condensate trapped in an optical lattice, where Bloch oscillations are forced by gravity. The fine-tuning of the scattering length down to 0.1 a_(0) and the micrometric sizes of the atomic sample make our system a very promising candidate for measuring forces with high spatial resolution. Our technique can be in principle extended to other measurement schemes opening new possibilities in the field of trapped atom interferometry.

39K Bose-Einstein condensate with tunable interactions.

We produce a Bose-Einstein condensate of 39K atoms. Condensation of this species with a naturally small and negative scattering length is achieved by a combination of sympathetic cooling with 87Rb and direct evaporation, exploiting the magnetic tuning of both inter- and intraspecies interactions at Feshbach resonances. We explore the tunability of the self-interactions by studying the expansion and the stability of the condensate. We find that a 39K condensate is interesting for future experiments requiring a weakly-interacting Bose gas.

Antigenically activated avian erythrocytes release cytokine-like factors: a conserved phylogenetic function discovered in fish.

Fish erythrocytes are endowed with the ability to produce cytokine like factors when stimulated with Candida albicans (Ca). To evaluate whether similar activities are still conserved in bird erythrocytes (BE), a morphological, cytochemical and immunological evaluation was conducted on peripheral cells in chickens (Gallus gallus). BE form rosettes with monocytes (Mo)-macrophages (MØ), and Mo-MØ according to cytochemical analysis to maintain phagocytic functions across the evolution. Finally, Ca-activated BE release in the supernatants cytokine like-factors that enhance Mo-MØ phagocytosis (interferon-gamma-like activity) and inhibit Mo-MØ migration in agarose (migration inhibitory factor activity). In conclusion, bird erythrocytes, as nonimmune cells, are able to participate in the immune response contributing to the host defence.