PT-symmetry breaking and universal chirality in a PT-symmetric ring

We investigate the properties of an $N$-site tight-binding lattice with periodic boundary condition (PBC) in the presence of a pair of gain and loss impurities $\pm i\gamma$, and two tunneling amplitudes $t_0,t_b$ that are constant along the two paths that connect them. We show that the parity and time-reversal (\mP\mT)-symmetric phase of the lattice with PBC is robust, insensitive to the distance between the impurities, and that the critical impurity strength for PT-symmetry breaking is given by $\gamma_{PT}=|t_0-t_b|$. We study the time-evolution of a typical wave packet, initially localized on a single site, across the PT-symmetric phase boundary. We find that it acquires chirality with increasing $\gamma$, and the chirality reaches a universal maximum value at the threshold, $\gamma=\gamma_{PT}$, irrespective of the initial location of the wave packet or the lattice parameters. Our results imply that PT-symmetry breaking on a lattice with PBC has consequences that have no counterpart in open chains.Comment: 5 pages, 3 figure

Degrees and signatures of broken PT-symmetry in (non-uniform) lattices

We investigate the robustness of parity- and time-reversal (\mP\mT) symmetric phase in an $N$-site lattice with position-dependent, parity-symmetric hopping function and a pair of imaginary, \mP\mT-symmetric impurities. We find that the "fragile" \mP\mT-symmetric phase in these lattices is stronger than its counterpart in a lattice with constant hopping. With an open system in mind, we explore the degrees of broken \mP\mT-symmetry and their signatures in single-particle wavepacket evolution. We predict that when the \mP\mT-symmetric impurities are closest to each other, the time evolution of a wavepacket in an even-$N$ lattice is remarkably different from that in an odd-$N$ lattice. Our results suggest that \mP\mT-symmetry breaking in such lattices is accompanied by rich, hitherto unanticipated, phenomena.Comment: 5 figure

Optical waveguide arrays: quantum effects and PT symmetry breaking

Over the last two decades, advances in fabrication have led to significant progress in creating patterned heterostructures that support either carriers, such as electrons or holes, with specific band structure or electromagnetic waves with a given mode structure and dispersion. In this article, we review the properties of light in coupled optical waveguides that support specific energy spectra, with or without the effects of disorder, that are well-described by a Hermitian tight-binding model. We show that with a judicious choice of the initial wave packet, this system displays the characteristics of a quantum particle, including transverse photonic transport and localization, and that of a classical particle. We extend the analysis to non-Hermitian, parity and time-reversal ($\mathcal{PT}$) symmetric Hamiltonians which physically represent waveguide arrays with spatially separated, balanced absorption or amplification. We show that coupled waveguides are an ideal candidate to simulate $\mathcal{PT}$-symmetric Hamiltonians and the transition from a purely real energy spectrum to a spectrum with complex conjugate eigenvalues that occurs in them.Comment: 16 pages, 12 figures, Invited Review for European Physics Journal - Applied Physic

Terahertz Waveguiding in Silicon-Core Fibers

We propose the use of a silicon-core optical fiber for terahertz (THz) waveguide applications. Finite-difference time-domain simulations have been performed based on a cylindrical waveguide with a silicon core and silica cladding. High-resistivity silicon has a flat dispersion over a 0.1 - 3 THz range, making it viable for propagation of tunable narrowband CW THz and possibly broadband picosecond pules of THz radiation. Simulations show the propagation dynamics and the integrated intensity, from which transverse mode profiles and absorption lengths are extraced. It is found that for 140 - 250 micron core diameters the mode is primarily confined to the core, such that the overall absorbance is only slightly less than in bulk polycrystalline silicon.Comment: 6 pages, 3 figures, journal submissio

PT-symmetry breaking and maximal chirality in a nonuniform PT-symmetric ring

We study the properties of an N-site tight-binding ring with parity and time-reversal (PT) symmetric, Hermitian, site-dependent tunneling and a pair of non-Hermitian, PT-symmetric, loss and gain impurities $\pm i\gamma$. The properties of such lattices with open boundary conditions have been intensely explored over the past two years. We numerically investigate the PT-symmetric phase in a ring with a position-dependent tunneling function $t_\alpha(k)=[k(N-k)]^{\alpha/2}$ that, in an open lattice, leads to a strengthened PT-symmetric phase, and study the evolution of the PT-symmetric phase from the open chain to a ring. We show that, generally, periodic boundary conditions weaken the PT-symmetric phase, although for experimentally relevant lattice sizes $N \sim 50$, it remains easily accessible. We show that the chirality, quantified by the (magnitude of the) average transverse momentum of a wave packet, shows a maximum at the PT-symmetric threshold. Our results show that although the wavepacket intensity increases monotonically across the PT-breaking threshold, the average momentum decays monotonically on both sides of the threshold.Comment: 11 pages, 5 figures, preprin

Dusp3 and Psme3 are associated with murine susceptibility to Staphylococcus aureus infection and human sepsis.

Using A/J mice, which are susceptible to Staphylococcus aureus, we sought to identify genetic determinants of susceptibility to S. aureus, and evaluate their function with regard to S. aureus infection. One QTL region on chromosome 11 containing 422 genes was found to be significantly associated with susceptibility to S. aureus infection. Of these 422 genes, whole genome transcription profiling identified five genes (Dcaf7, Dusp3, Fam134c, Psme3, and Slc4a1) that were significantly differentially expressed in a) S. aureus -infected susceptible (A/J) vs. resistant (C57BL/6J) mice and b) humans with S. aureus blood stream infection vs. healthy subjects. Three of these genes (Dcaf7, Dusp3, and Psme3) were down-regulated in susceptible vs. resistant mice at both pre- and post-infection time points by qPCR. siRNA-mediated knockdown of Dusp3 and Psme3 induced significant increases of cytokine production in S. aureus-challenged RAW264.7 macrophages and bone marrow derived macrophages (BMDMs) through enhancing NF-κB signaling activity. Similar increases in cytokine production and NF-κB activity were also seen in BMDMs from CSS11 (C57BL/6J background with chromosome 11 from A/J), but not C57BL/6J. These findings suggest that Dusp3 and Psme3 contribute to S. aureus infection susceptibility in A/J mice and play a role in human S. aureus infection

Two contemporaneous mitogenomes from terminal Pleistocene burials in eastern Beringia

Pleistocene residential sites with multiple contemporaneous human burials are extremely rare in the Americas. We report mitochondrial genomic variation in the first multiple mitochondrial genomes from a single prehistoric population: two infant burials (USR1 and USR2) from a common interment at the Upward Sun River Site in central Alaska dating to ~11,500 calendar years before present (cal B.P.). Using a targeted capture method and next-generation sequencing we determined that the USR1 infant possessed variants that define mitochondrial lineage C1b, while the USR2 genome falls at the root of lineage B2, allowing us to refine younger coalescence age estimates for these two clades. C1b and B2 are rare to absent in modern populations of Northern North America. Documentation of these lineages at this location in the Late Pleistocene provides evidence for the extent of mitochondrial diversity in early Beringian populations, which supports the expectations of the Beringian Standstill Model