154 research outputs found
Anomalous Expansion of Attractively Interacting Fermionic Atoms in an Optical Lattice
Strong correlations can dramatically modify the thermodynamics of a quantum
many-particle system. Especially intriguing behaviour can appear when the
system adiabatically enters a strongly correlated regime, for the interplay
between entropy and strong interactions can lead to counterintuitive effects. A
well known example is the so-called Pomeranchuk effect, occurring when liquid
3He is adiabatically compressed towards its crystalline phase. Here, we report
on a novel anomalous, isentropic effect in a spin mixture of attractively
interacting fermionic atoms in an optical lattice. As we adiabatically increase
the attraction between the atoms we observe that the gas, instead of
contracting, anomalously expands. This expansion results from the combination
of two effects induced by pair formation in a lattice potential: the
suppression of quantum fluctuations as the attraction increases, which leads to
a dominant role of entropy, and the progressive loss of the spin degree of
freedom, which forces the gas to excite additional orbital degrees of freedom
and expand to outer regions of the trap in order to maintain the entropy. The
unexpected thermodynamics we observe reveal fundamentally distinctive features
of pairing in the fermionic Hubbard model.Comment: 6 pages (plus appendix), 6 figure
High energy limits of Laplace-type and Dirac-type eigenfunctions and frame flows
We relate high-energy limits of Laplace-type and Dirac-type operators to
frame flows on the corresponding manifolds, and show that the ergodicity of
frame flows implies quantum ergodicity in an appropriate sense for those
operators. Observables for the corresponding quantum systems are matrix-valued
pseudodifferential operators and therefore the system remains non-commutative
in the high-energy limit. We discuss to what extent the space of stationary
high-energy states behaves classically.Comment: 26 pages, latex2
Thermometry with spin-dependent lattices
We propose a method for measuring the temperature of strongly correlated
phases of ultracold atom gases confined in spin-dependent optical lattices. In
this technique, a small number of "impurity" atoms--trapped in a state that
does not experience the lattice potential--are in thermal contact with atoms
bound to the lattice. The impurity serves as a thermometer for the system
because its temperature can be straightforwardly measured using time-of-flight
expansion velocity. This technique may be useful for resolving many open
questions regarding thermalization in these isolated systems. We discuss the
theory behind this method and demonstrate proof-of-principle experiments,
including the first realization of a 3D spin-dependent lattice in the strongly
correlated regime.Comment: 22 pages, 8 figures v2: Several references added; Section on heating
rates updated to include dipole fluctuation terms; Section added on the
limitations of the proposed method. To appear in New Journal of Physic
Quantum transport in ultracold atoms
Ultracold atoms confined by engineered magnetic or optical potentials are
ideal systems for studying phenomena otherwise difficult to realize or probe in
the solid state because their atomic interaction strength, number of species,
density, and geometry can be independently controlled. This review focuses on
quantum transport phenomena in atomic gases that mirror and oftentimes either
better elucidate or show fundamental differences with those observed in
mesoscopic and nanoscopic systems. We discuss significant progress in
performing transport experiments in atomic gases, contrast similarities and
differences between transport in cold atoms and in condensed matter systems,
and survey inspiring theoretical predictions that are difficult to verify in
conventional setups. These results further demonstrate the versatility offered
by atomic systems in the study of nonequilibrium phenomena and their promise
for novel applications.Comment: 24 pages, 7 figures. A revie
A Rigorous Geometric Derivation of the Chiral Anomaly in Curved Backgrounds
We discuss the chiral anomaly for a Weyl field in a curved background and show that a novel index theorem for the Lorentzian Dirac operator can be applied to describe the gravitational chiral anomaly. A formula for the total charge generated by the gravitational and gauge field background is derived directly in Lorentzian signature and in a mathematically rigorous manner. It contains a term identical to the integrand in the Atiyah–Singer index theorem and another term involving the η -invariant of the Cauchy hypersurfaces
The split property for locally covariant quantum field theories in curved spacetime
The split property expresses the way in which local regions of spacetime define subsystems of a quantum field theory. It is known to hold for general theories in Minkowski space under the hypothesis of nuclearity. Here, the split property is discussed for general locally covariant quantum field theories in arbitrary globally hyperbolic curved spacetimes, using a spacetime deformation argument to transport the split property from one spacetime to another. It is also shown how states obeying both the split and (partial) Reeh–Schlieder properties can be constructed, providing standard split inclusions of certain local von Neumann algebras. Sufficient conditions are given for the theory to admit such states in ultrastatic spacetimes, from which the general case follows. A number of consequences are described, including the existence of local generators for global gauge transformations, and the classification of certain local von Neumann algebras. Similar arguments are applied to the distal split property and circumstances are exhibited under which distal splitting implies the full split property
Shared Genetic Etiology Between Alcohol Dependence and Major Depressive Disorder
The clinical comorbidity of alcohol dependence (AD) and
major depressive disorder (MDD) is well established,
whereas genetic factors influencing co-occurrence remain
unclear. A recent study using polygenic risk scores (PRS)
calculated based on the first-wave Psychiatric Genomics
Consortium MDD meta-analysis (PGC-MDD1) suggests a
modest shared genetic contribution to MDD and AD. Using a
(∼10 fold) larger discovery sample, we calculated PRS
based on the second wave (PGC-MDD2) of results, in a
severe AD case–control target sample. We found significant associations between AD disease status and MDD-PRS derived from both PGC-MDD2 (most informative
P-threshold=1.0, P=0.00063, R2=0.533%) and PGCMDD1
(P-threshold=0.2, P=0.00014, R2=0.663%) metaanalyses;
the larger discovery sample did not yield
additional predictive power. In contrast, calculating PRS in a MDD target sample yielded increased power when using
PGC-MDD2 (P-threshold=1.0, P=0.000038, R2=1.34%)
versus PGC-MDD1 (P-threshold=1.0, P=0.0013,
R2=0.81%). Furthermore, when calculating PGC-MDD2
PRS in a subsample of patients with AD recruited explicitly excluding comorbid MDD, significant associations were still found (n=331; P-threshold=1.0, P=0.042, R2=0.398%). Meanwhile, in the subset of patients in which MDD was not the explicit exclusion criteria, PRS predicted more variance (n=999; P-threshold=1.0, P=0.0003, R2=0.693%). Our findings replicate the reported genetic overlap between AD and MDD and also suggest the need for improved, rigorous phenotyping to identify true shared cross-disorder genetic factors. Larger target samples are needed to reduce noise and take advantage of increasing discovery sample size
The split property for quantum field theories in flat and curved spacetimes
The split property expresses a strong form of independence of spacelike separated regions in algebraic quantum field theory. In Minkowski spacetime, it can be proved under hypotheses of nuclearity. An expository account is given of nuclearity and the split property, and connections are drawn to the theory of quantum energy inequalities. In addition, a recent proof of the split property for quantum field theory in curved spacetimes is outlined, emphasising the essential ideas
Sexual dysfunction during treatment with serotonergic and noradrenergic antidepressants: Clinical description and the role of the 5-HTTLPR
Objectives. Sexual dysfunction (SD) is a frequently reported side-effect of antidepressant treatment, particularly of selective serotonin reuptake inhibitors (SSRIs). In the multicentre clinical and pharmacogenetic GENDEP study (Genome-based Therapeutic Drugs for Depression), the effect of the serotonin transporter gene promoter polymorphism 5-HTTLPR on sexual function was investigated during treatment with escitalopram (SSRI) and nortriptyline (tricyclic antidepressant). Methods. A total of 494 subjects with an episode of DSM-IV major depression were randomly assigned to treatment with escitalopram or nortriptyline. Over 12 weeks, depressive symptoms and SD were measured weekly with the Montgomery-Asberg Depression Rating Scale, the Antidepressant Side-Effect Checklist, the UKU Side Effect Rating Scale, and the Sexual Functioning Questionnaire. Results. The incidence of reported SD after 12 weeks of treatment was relatively low, and did not differ significantly between antidepressants (14.9% escitalopram, 19.7% nortriptyline). There was no significant interaction between the 5-HTTLPR and antidepressant on SD. Improvement in depressive symptoms and younger age were both associated with lower SD. The effect of age on SD may have been moderated by the 5-HTTLPR. Conclusions. In GENDEP, rates of reported SD during treatment were lower than those described in previous reports. There was no apparent effect of the 5-HTTLPR on the observed decline in SD. © 2011 Informa Healthcare.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Genome-wide association for major depression through age at onset stratification
BACKGROUND: Major depressive disorder (MDD) is a disabling mood disorder, and despite a known heritable component, a large meta-analysis of genome-wide association studies revealed no replicable genetic risk variants. Given prior evidence of heterogeneity by age at onset in MDD, we tested whether genome-wide significant risk variants for MDD could be identified in cases subdivided by age at onset.
METHODS: Discovery case-control genome-wide association studies were performed where cases were stratified using increasing/decreasing age-at-onset cutoffs; significant single nucleotide polymorphisms were tested in nine independent replication samples, giving a total sample of 22,158 cases and 133,749 control subjects for subsetting. Polygenic score analysis was used to examine whether differences in shared genetic risk exists between earlier and adult-onset MDD with commonly comorbid disorders of schizophrenia, bipolar disorder, Alzheimer’s disease, and coronary artery disease.
RESULTS: We identified one replicated genome-wide significant locus associated with adult-onset (>27 years) MDD (rs7647854, odds ratio: 1.16, 95% confidence interval: 1.11–1.21, p = 5.2 × 10-11). Using polygenic score analyses, we show that earlier-onset MDD is genetically more similar to schizophrenia and bipolar disorder than adult-onset MDD.
CONCLUSIONS: We demonstrate that using additional phenotype data previously collected by genetic studies to tackle phenotypic heterogeneity in MDD can successfully lead to the discovery of genetic risk factor despite reduced sample size. Furthermore, our results suggest that the genetic susceptibility to MDD differs between adult- and earlier-onset MDD, with earlier-onset cases having a greater genetic overlap with schizophrenia and bipolar disorder
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