751 research outputs found
Universal properties of many-body delocalization transitions
We study the dynamical melting of "hot" one-dimensional many-body localized
systems. As disorder is weakened below a critical value these non-thermal
quantum glasses melt via a continuous dynamical phase transition into classical
thermal liquids. By accounting for collective resonant tunneling processes, we
derive and numerically solve an effective model for such quantum-to-classical
transitions and compute their universal critical properties. Notably, the
classical thermal liquid exhibits a broad regime of anomalously slow
sub-diffusive equilibration dynamics and energy transport. The subdiffusive
regime is characterized by a continuously evolving dynamical critical exponent
that diverges with a universal power at the transition. Our approach elucidates
the universal long-distance, low-energy scaling structure of many-body
delocalization transitions in one dimension, in a way that is transparently
connected to the underlying microscopic physics.Comment: 12 pages, 6 figures; major changes from v1, including a modified
approach and new emphasis on conventional MBL systems rather than their
critical variant
Localization-protected order in spin chains with non-Abelian discrete symmetries
We study the non-equilibrium phase structure of the three-state random
quantum Potts model in one dimension. This spin chain is characterized by a
non-Abelian symmetry recently argued to be incompatible with the
existence of a symmetry-preserving many-body localized (MBL) phase. Using exact
diagonalization and a finite-size scaling analysis, we find that the model
supports two distinct broken-symmetry MBL phases at strong disorder that either
break the clock symmetry or a chiral
symmetry. In a dual formulation, our results indicate the existence of a stable
finite-temperature topological phase with MBL-protected parafermionic end zero
modes. While we find a thermal symmetry-preserving regime for weak disorder,
scaling analysis at strong disorder points to an infinite-randomness critical
point between two distinct broken-symmetry MBL phases.Comment: 5 pages, 3 figures main text; 6 pages, 3 figures supplemental
material; Version 2 includes a corrected the form of the chiral order
parameter, and corresponding data, as well as larger system size numerics,
with no change to the phase structur
Particle-hole symmetry, many-body localization, and topological edge modes
We study the excited states of interacting fermions in one dimension with
particle-hole symmetric disorder (equivalently, random-bond XXZ chains) using a
combination of renormalization group methods and exact diagonalization. Absent
interactions, the entire many-body spectrum exhibits infinite-randomness
quantum critical behavior with highly degenerate excited states. We show that
though interactions are an irrelevant perturbation in the ground state, they
drastically affect the structure of excited states: even arbitrarily weak
interactions split the degeneracies in favor of thermalization (weak disorder)
or spontaneously broken particle-hole symmetry, driving the system into a
many-body localized spin glass phase (strong disorder). In both cases, the
quantum critical properties of the non-interacting model are destroyed, either
by thermal decoherence or spontaneous symmetry breaking. This system then has
the interesting and counterintuitive property that edges of the many-body
spectrum are less localized than the center of the spectrum. We argue that our
results rule out the existence of certain excited state symmetry-protected
topological orders.Comment: 9 pages. 7 figure
Effect of the Salmonella Pathogenicity Island 2 Type III Secretion System on Salmonella Survival in Activated Chicken Macrophage-Like HD11 Cells
In order to better identify the role of the Salmonella pathogenicity island 2 (SPI-2) type III secretion system (T3SS) in chickens, we used the well-known gentamicin protection assay with activated HD11 cells. HD11 cells are a macrophage-like chicken cell line that can be stimulated with phorbol 12-myristate 13-acetate (PMA) to exhibit more macrophage-like morphology and greater production of reactive oxygen species (ROS). Activated HD11 cells were infected with a wild-type Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium) strain, a SPI-2 mutant S. Typhimurium strain, a wild-type Salmonella enterica subspecies enterica serovar Enteritidis (S. Enteritidis) strain, a SPI-2 mutant S. Enteritidis strain, or a non-pathogenic Escherichia coli (E. coli) strain. SPI-2 mutant strains were found to survive as well as their parent strain at all time points post-uptake (PU) by the HD11 cells, up to 24 h PU, while the E. coli strain was no longer recoverable by 3 h PU. We can conclude from these observations that the SPI-2 T3SS of S. Typhimurium and S. Enteritidis is not important for survival of Salmonella in the activated macrophage-like HD11 cell line, and that Salmonella must employ other mechanisms for survival in this environment, as E. coli is effectively eliminated
Sequential quantum simulation of spin chains with a single circuit QED device
Quantum simulation of many-body systems in materials science and chemistry
are promising application areas for quantum computers. However, the limited
scale and coherence of near-term quantum processors pose a significant obstacle
to realizing this potential. Here, we theoretically outline how a
single-circuit quantum electrodynamics (cQED) device, consisting of a transmon
qubit coupled to a long-lived cavity mode, can be used to simulate the ground
state of a highly-entangled quantum many-body spin chain. We exploit recently
developed methods for implementing quantum operations to sequentially build up
a matrix product state (MPS) representation of a many-body state. This approach
re-uses the transmon qubit to read out the state of each spin in the chain and
exploits the large state space of the cavity as a quantum memory encoding
inter-site correlations and entanglement. We show, through simulation, that
analog (pulse-level) control schemes can accurately prepare a known MPS
representation of a quantum critical spin chain in significantly less time than
digital (gate-based) methods, thereby reducing the exposure to decoherence. We
then explore this analog-control approach for the variational preparation of an
unknown ground state. We demonstrate that the large state space of the cavity
can be used to replace multiple qubits in a qubit-only architecture, and could
therefore simplify the design of quantum processors for materials simulation.
We explore the practical limitations of realistic noise and decoherence and
discuss avenues for scaling this approach to more complex problems that
challenge classical computational methods.Comment: 9 pages, 4 figure
Fluorination influences the bioisostery of myo-inositol pyrophosphate analogs
Inositol pyrophosphates (PP-IPs) are densely
phosphorylated messenger molecules involved in numerous
biological processes. PP-IPs contain one or two pyrophosphate
group(s) attached to a phosphorylated myo-inositol ring. 5PP-IP5 is
the most abundant PP-IP in human cells. To investigate the function
and regulation by PP-IPs in biological contexts, metabolically stable
analogs have been developed. Here, we report the synthesis of a new
fluorinated phosphoramidite reagent and its application for the
synthesis of a difluoromethylene bisphosphonate analog of 5PP-IP5.
Subsequently, the properties of all currently reported analogs were
benchmarked using a number of biophysical and biochemical
methods, including co-crystallization, ITC, kinase activity assays and
chromatography. Together, the results showcase how small structural
alterations of the analogs can have notable effects on their properties
in a biochemical setting and will guide in the choice of the most
suitable analog(s) for future investigations
Superuniversality from disorder at two-dimensional topological phase transitions
We investigate the effects of quenched randomness on topological quantum
phase transitions in strongly interacting two-dimensional systems. We focus
first on transitions driven by the condensation of a subset of fractionalized
quasiparticles (`anyons') identified with `electric charge' excitations of a
phase with intrinsic topological order. All other anyons have nontrivial mutual
statistics with the condensed subset and hence become confined at the anyon
condensation transition. Using a combination of microscopically exact duality
transformations and asymptotically exact real-space renormalization group
techniques applied to these two-dimensional disordered gauge theories, we argue
that the resulting critical scaling behavior is `superuniversal' across a wide
range of such condensation transitions, and is controlled by the same
infinite-randomness fixed point as that of the 2D random transverse-field Ising
model. We validate this claim using large-scale quantum Monte Carlo simulations
that allow us to extract zero-temperature critical exponents and correlation
functions in (2+1)D disordered interacting systems. We discuss generalizations
of these results to a large class of ground-state and excited-state topological
transitions in systems with intrinsic topological order as well as those where
topological order is either protected or enriched by global symmetries. When
the underlying topological order and the symmetry group are Abelian, our
results provide prototypes for topological phase transitions between distinct
many-body localized phases.Comment: 33 pages, 35 figures; published versio
Homologous and heterologous desensitization of guanylyl cyclase-B signaling in GH3 somatolactotropes
The guanylyl cyclases, GC-A and GC-B, are selective receptors for atrial and C-type natriuretic peptides (ANP and CNP, respectively). In the anterior pituitary, CNP and GC-B are major regulators of cGMP production in gonadotropes and yet mouse models of disrupted CNP and GC-B indicate a potential role in growth hormone secretion. In the current study, we investigate the molecular and pharmacological properties of the CNP/GC-B system in somatotrope lineage cells. Primary rat pituitary and GH3 somatolactotropes expressed functional GC-A and GC-B receptors that had similar EC50 properties in terms of cGMP production. Interestingly, GC-B signaling underwent rapid homologous desensitization in a protein phosphatase 2A (PP2A)-dependent manner. Chronic exposure to either CNP or ANP caused a significant down-regulation of both GC-A- and GC-B-dependent cGMP accumulation in a ligand-specific manner. However, this down-regulation was not accompanied by alterations in the sub-cellular localization of these receptors. Heterologous desensitization of GC-B signaling occurred in GH3 cells following exposure to either sphingosine-1-phosphate or thyrotrophin-releasing hormone (TRH). This heterologous desensitization was protein kinase C (PKC)-dependent, as pre-treatment with GF109203X prevented the effect of TRH on CNP/GC-B signaling. Collectively, these data indicate common and distinct properties of particulate guanylyl cyclase receptors in somatotropes and reveal that independent mechanisms of homologous and heterologous desensitization occur involving either PP2A or PKC. Guanylyl cyclase receptors thus represent potential novel therapeutic targets for treating growth-hormone-associated disorders
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