Thermography of the superfluid transition in a strongly interacting Fermi gas.

Heat transport can serve as a fingerprint identifying different states of matter. In a normal liquid, a hotspot diffuses, whereas in a superfluid, heat propagates as a wave called "second sound." Direct imaging of heat transport is challenging, and one usually resorts to detecting secondary effects. In this study, we establish thermography of a strongly interacting atomic Fermi gas, whose radio-frequency spectrum provides spatially resolved thermometry with subnanokelvin resolution. The superfluid phase transition was directly observed as the sudden change from thermal diffusion to second-sound propagation and is accompanied by a peak in the second-sound diffusivity. This method yields the full heat and density response of the strongly interacting Fermi gas and therefore all defining properties of Landau's two-fluid hydrodynamics.

Photons think inside the box.

Light confined to a sheet offers a glimpse into low-dimensional quantum gases.

Crystallization of bosonic quantum Hall states in a rotating quantum gas.

The dominance of interactions over kinetic energy lies at the heart of strongly correlated quantum matter, from fractional quantum Hall liquids1, to atoms in optical lattices2 and twisted bilayer graphene3. Crystalline phases often compete with correlated quantum liquids, and transitions between them occur when the energy cost of forming a density wave approaches zero. A prime example occurs for electrons in high-strength magnetic fields, where the instability of quantum Hall liquids towards a Wigner crystal4-9 is heralded by a roton-like softening of density modulations at the magnetic length7,10-12. Remarkably, interacting bosons in a gauge field are also expected to form analogous liquid and crystalline states13-21. However, combining interactions with strong synthetic magnetic fields has been a challenge for experiments on bosonic quantum gases18,21. Here we study the purely interaction-driven dynamics of a Landau gauge Bose-Einstein condensate22 in and near the lowest Landau level. We observe a spontaneous crystallization driven by condensation of magneto-rotons7,10, excitations visible as density modulations at the magnetic length. Increasing the cloud density smoothly connects this behaviour to a quantum version of the Kelvin-Helmholtz hydrodynamic instability, driven by the sheared internal flow profile of the rapidly rotating condensate. At long times the condensate self-organizes into a persistent array of droplets separated by vortex streets, which are stabilized by a balance of interactions and effective magnetic forces.

Cohort profile: the Men and Parenting Pathways (MAPP) Study: a longitudinal Australian cohort study of men's mental health and well-being at the normative age for first-time fatherhood.

PURPOSE: The Men and Parenting Pathways (MAPP) Study is a prospective investigation of men's mental health and well-being across the normative age for transitioning to fatherhood. This includes trajectories and outcomes for men who do and do not become fathers across five annual waves of the study. PARTICIPANTS: Australian resident, English-speaking men aged 28-32 years at baseline were eligible. Recruitment was over a 2-year period (2015-2017) via social and traditional media and through engagement with study partners. Eight hundred and eighteen eligible men consented to participate. Of these, 664 men completed the first online survey of whom 608 consented to ongoing participation. Of the ongoing sample, 83% have participated in at least two of the first three annual online surveys. FINDINGS TO DATE: Three waves of data collection are complete. The first longitudinal analysis of MAPP data, published in 2020, identified five profiles that characterise men's patterns of depressive symptom severity and presentations of anger. Profiles indicating pronounced anger and depressive symptoms were associated with fathers' lack of perceived social support, and problems with coparenting and bonding with infants. In a second study, MAPP data were combined with three other Australian cohorts in a meta-analysis of associations between fathers' self-reported sleep problems up to 3 years postpartum and symptoms of depression, anxiety and stress. Adjusted meta-analytic associations between paternal sleep and mental health risk ranged from 0.25 to 0.37. FUTURE PLANS: MAPP is an ongoing cohort study. Waves 4 and 5 data will be ready for analyses at the end of 2021. Future investigations will include crossed-lagged and trajectory analyses that assess inter-relatedness and changing social networks, mental health, work and family life. A nested study of COVID-19 pandemic-related mental health and coping will add two further waves of data collection in a subsample of MAPP participants.

Geometric squeezing into the lowest Landau level.

The equivalence between particles under rotation and charged particles in a magnetic field relates phenomena as diverse as spinning atomic nuclei, weather patterns, and the quantum Hall effect. For such systems, quantum mechanics dictates that translations along different directions do not commute, implying a Heisenberg uncertainty relation between spatial coordinates. We implement squeezing of this geometric quantum uncertainty, resulting in a rotating Bose-Einstein condensate occupying a single Landau gauge wave function. We resolve the extent of zero-point cyclotron orbits and demonstrate geometric squeezing of the orbits' centers 7 decibels below the standard quantum limit. The condensate attains an angular momentum exceeding 1000 quanta per particle and an interatomic distance comparable to the cyclotron orbit. This offers an alternative route toward strongly correlated bosonic fluids.

Universal sound diffusion in a strongly interacting Fermi gas.

Transport of strongly interacting fermions is crucial for the properties of modern materials, nuclear fission, the merging of neutron stars, and the expansion of the early Universe. Here, we observe a universal quantum limit of diffusivity in a homogeneous, strongly interacting atomic Fermi gas by studying sound propagation and its attenuation through the coupled transport of momentum and heat. In the normal state, the sound diffusivity D monotonically decreases upon lowering the temperature, in contrast to the diverging behavior of weakly interacting Fermi liquids. Below the superfluid transition temperature, D attains a universal value set by the ratio of Planck's constant and the particle mass. Our findings inform theories of fermion transport, with relevance for hydrodynamic flow of electrons, neutrons, and quarks.

Spectral Response and Contact of the Unitary Fermi Gas.

We measure radio frequency (rf) spectra of the homogeneous unitary Fermi gas at temperatures ranging from the Boltzmann regime through quantum degeneracy and across the superfluid transition. For all temperatures, a single spectral peak is observed. Its position smoothly evolves from the bare atomic resonance in the Boltzmann regime to a frequency corresponding to nearly one Fermi energy at the lowest temperatures. At high temperatures, the peak width reflects the scattering rate of the atoms, while at low temperatures, the width is set by the size of fermion pairs. Above the superfluid transition, and approaching the quantum critical regime, the width increases linearly with temperature, indicating non-Fermi-liquid behavior. From the wings of the rf spectra, we obtain the contact, quantifying the strength of short-range pair correlations. We find that the contact rapidly increases as the gas is cooled below the superfluid transition.

Boiling a Unitary Fermi Liquid.

We study the thermal evolution of a highly spin-imbalanced, homogeneous Fermi gas with unitarity limited interactions, from a Fermi liquid of polarons at low temperatures to a classical Boltzmann gas at high temperatures. Radio-frequency spectroscopy gives access to the energy, lifetime, and short-range correlations of Fermi polarons at low temperatures T. In this regime, we observe a characteristic T^{2} dependence of the spectral width, corresponding to the quasiparticle decay rate expected for a Fermi liquid. At high T, the spectral width decreases again towards the scattering rate of the classical, unitary Boltzmann gas, ∝T^{-1/2}. In the transition region between the quantum degenerate and classical regime, the spectral width attains its maximum, on the scale of the Fermi energy, indicating the breakdown of a quasiparticle description. Density measurements in a harmonic trap directly reveal the majority dressing cloud surrounding the minority spins and yield the compressibility along with the effective mass of Fermi polarons.

Coparenting Competence in Parents of Children with ASD: A Marker of Coparenting Quality.

The coparenting relationship has been linked to parenting stress, parenting self-efficacy and many other concerns associated with the development of children with ASD. Parents of children with ASD (N = 22) were interviewed to explore three domains of their coparenting relationship; (1) adaptation to the emergence of their child's autism, (2) parenting their child with ASD, (3) expectations for their child's developmental outcomes. The concept of coparenting competence, developed during analysis, describes collective perceptions of parenting efficacy. Parents linked perceptions of coparenting competence to their, ability to cope with diagnosis and parenting, motivation to do what they could for their child, and hopes for their child's development. The concept of coparenting competence could play an important role in future research and intervention.

Two- and three-body contacts in the unitary Bose gas.

In many-body systems governed by pairwise contact interactions, a wide range of observables is linked by a single parameter, the two-body contact, which quantifies two-particle correlations. This profound insight has transformed our understanding of strongly interacting Fermi gases. Using Ramsey interferometry, we studied coherent evolution of the resonantly interacting Bose gas, and we show here that it cannot be explained by only pairwise correlations. Our experiments reveal the crucial role of three-body correlations arising from Efimov physics and provide a direct measurement of the associated three-body contact.

Connecting Berezinskii-Kosterlitz-Thouless and BEC Phase Transitions by Tuning Interactions in a Trapped Gas.

We study the critical point for the emergence of coherence in a harmonically trapped two-dimensional Bose gas with tunable interactions. Over a wide range of interaction strengths we find excellent agreement with the classical-field predictions for the critical point of the Berezinskii-Kosterlitz-Thouless (BKT) superfluid transition. This allows us to quantitatively show, without any free parameters, that the interaction-driven BKT transition smoothly converges onto the purely quantum-statistical Bose-Einstein condensation transition in the limit of vanishing interactions.

Men's experiences of grandfatherhood: a welcome surprise.

The present-day involvement of men in many facets of childrearing stands in contrast to previous eras when men accepted that the major task of fathering was to provide a secure income to support the family. This imperative often required long hours away from the family. However, when men whose contact with children has been limited due to work and cultural constraints retire, their newly acquired lifestyle may bring fresh opportunities for involvement with grandchildren. An important question therefore concerns the impact of caring for young children on men's perceptions of their role as grandfathers. This interview study explores the experiences of 19 Australian grandfathers. The analysis found themes that relate to relationships and change, as well as themes concerning core beliefs and existential questions. The findings demonstrate the potential for insight into family relationships and personal growth in older age when studying the topic of grandparenting and caring from the male perspective.

Men's experiences of grandfatherhood: a welcome surprise.

The present-day involvement of men in many facets of childrearing stands in contrast to previous eras when men accepted that the major task of fathering was to provide a secure income to support the family. This imperative often required long hours away from the family. However, when men whose contact with children has been limited due to work and cultural constraints retire, their newly acquired lifestyle may bring fresh opportunities for involvement with grandchildren. An important question therefore concerns the impact of caring for young children on men's perceptions of their role as grandfathers. This interview study explores the experiences of 19 Australian grandfathers. The analysis found themes that relate to relationships and change, as well as themes concerning core beliefs and existential questions. The findings demonstrate the potential for insight into family relationships and personal growth in older age when studying the topic of grandparenting and caring from the male perspective.

Stability of a unitary Bose gas.

We study the stability of a thermal (39)K Bose gas across a broad Feshbach resonance, focusing on the unitary regime, where the scattering length a exceeds the thermal wavelength λ. We measure the general scaling laws relating the particle-loss and heating rates to the temperature, scattering length, and atom number. Both at unitarity and for positive a<<λ we find agreement with three-body theory. However, for a<0 and away from unitarity, we observe significant four-body decay. At unitarity, the three-body loss coefficient, L(3) proportional λ(4), is 3 times lower than the universal theoretical upper bound. This reduction is a consequence of species-specific Efimov physics and makes (39)K particularly promising for studies of many-body physics in a unitary Bose gas.

Persistent currents in spinor condensates.

We create and study persistent currents in a toroidal two-component Bose gas, consisting of 87Rb atoms in two different spin states. For a large spin-population imbalance we observe supercurrents persisting for over two minutes. However, we find that the supercurrent is unstable for spin polarization below a well-defined critical value. We also investigate the role of phase coherence between the two spin components and show that only the magnitude of the spin-polarization vector, rather than its orientation in spin space, is relevant for supercurrent stability.

Fathers with mental illness: implications for clinicians and health services.

A significant proportion of fathers living with their natural, adopted, step or foster children experience mental illness. Psychiatric illness among fathers can have a devastating impact on children's wellbeing, and even milder forms of paternal mental illness can have serious developmental effects on children. While several pathways linking paternal mental illness with poor child outcomes have been identified, fathers' impaired parenting is an important, potentially malleable factor. Clinicians can assist fathers with mental illness and their families by proactively inquiring about children and by exploring fathering-focused psychological support.

The effects of early paternal depression on children's development.

OBJECTIVE: To examine the effects of paternal depression during children's first year on their wellbeing at 4-5 years of age using a large, representative sample of Australian families. DESIGN, SETTING AND PARTICIPANTS: Prospective study of Australian families from 2004 to 2008. Two-biological-parent families (n = 2620) from the Longitudinal Study of Australian Children were included if depression measures were available for both parents in 2004, behavioural and developmental measures were available for children in 2008, and the families had not separated by 2008. MAIN OUTCOME MEASURE: Child scores on the Strengths and Difficulties Questionnaire and on a set of Derived Outcome Indices, measured when the child was 4-5 years old. Logistic regression modelling was used to investigate how early paternal depression in 2004 influenced child outcomes 4 years later. RESULTS: Early paternal depression was a significant predictor of a range of poorer child outcomes (odds ratio [OR] for behavioural difficulties, 3.34 [95% CI, 3.06-3.65]; OR for a low development and wellbeing score, 2.70 [95% CI, 2.44-2.98]). These effects remained significant after controlling for both early maternal depression and later paternal depression (adjusted OR for behavioural difficulties, 1.93 [95% CI, 1.75-2.14]; OR for a low development and wellbeing score, 1.65 [95% CI, 1.48-1.85]). CONCLUSIONS: Depression in fathers during the first year of a child's life can have a detrimental impact on their child's behaviour, and social and emotional development at the point of school entry, in addition to and uniquely compared with depression in mothers. Early intervention to identify and address the mental health needs of fathers is required for the benefit of fathers, children and families.

Fathers online: learning about fatherhood through the internet.

In the transition to fatherhood, men face numerous challenges. Opportunities to learn new practices and gain support are limited, although the provisions of father-specific spaces such as fathers' antenatal classes or "responsible fathering" programs are important advances. This article explores how men use the social space of a father-specific Internet chat room to learn about fathering. Messages to an Australian-hosted, father-specific chat room (for fathers of infants or young children) were examined, and three overlapping themes illustrated men's perceptions of their transition to fatherhood. The themes concerned recognition of and response to a lack of social space, services, and support for new fathers. The implications for fathers' perinatal education are discussed.

Addressing depression and anxiety among new fathers.

Fathers may be unintentionally marginalised by perinatal health services and by the maternal focus of social practices surrounding new babies. There is increasing recognition that a fathers' depression and anxiety in the perinatal period can have serious consequences for his family. Health services could better support new fathers by providing them with information on parenting from a father's perspective, or by running father-specific sessions as part of routine antenatal care programs.

Men's Perceived Health Needs.

Cross-sectional survey data describing health priorities and needs perceived by men and women living in Newcastle, Australia are compared and contrasted with national health policies. The highest prevalence of felt needs for men were stress (13 percent), cost of medical care (10 percent) and money problems (9 percent); while stress (16 percent), overweight (16 percent) and money problems (15 percent) were highest for women. These contrast with the 2000 National Health Priorities of cancer, mental health, injury, cardiovascular health, diabetes and asthma. We conclude that men's perceived unmet health needs are similar to those of women; while sharing some commonalities, they also differ from health professional priorities. Incorporating felt needs into health service planning and delivery is a critical unmet challenge for government planners.