functions as a precursor of vitamin A in mammals (G. A. J. Pitt, in I. Osler, H. Gutmonn, and U. Solms, ed., Carotenoids-1971Carotenoids- , 1971). The enzymes and genes which mediate the biosynthesis of cyclic carotenoids such as 13-carotene are virtually unknown. We have elucidated for the first time the pathway for biosynthesis of these carotenoids at the level of enzyme-catalyzed reactions, using bacterial carotenoid biosynthesis genes. These genes were cloned from a phytopathogenic bacterium, Erwinia uredevora 20D3 (ATCC 19321)

Motivated by recent experimental advances in ultracold atoms, we analyze a non-Hermitian (NH) BCS Hamiltonian with a complex-valued interaction arising from inelastic scattering between fermions. We develop a mean-field theory to obtain a NH gap equation for order parameters, which are different from the standard BCS ones due to the inequivalence of left and right eigenstates in the NH physics. We find unconventional phase transitions unique to NH systems: superfluidity shows reentrant behavior with increasing dissipation, as a consequence of non-diagonalizable exceptional points, lines, and surfaces in the quasiparticle Hamiltonian for weak attractive interactions. For strong attractive interactions, the superfluid gap never collapses but is enhanced by dissipation due to an interplay between the BCS-BEC crossover and the quantum Zeno effect. Our results lay the groundwork for studies of fermionic superfluidity subject to inelastic collisions.

We investigate the Kondo effect in an open quantum system, motivated by recent experiments with ultracold alkaline-earth(-like) atoms. Because of inelastic collisions and the associated atom losses, this system is described by a complex-valued Kondo interaction and provides a non-Hermitian extension of the Kondo problem. We show that the non-Hermiticity induces anomalous reversion of renormalization-group flows which violate the g-theorem due to non-unitarity and produce a quantum phase transition unique to non-Hermiticity. Furthermore, we exactly solve the non-Hermitian Kondo Hamiltonian using a generalized Bethe ansatz method and find the critical line consistent with the renormalization-group flow. arXiv:1806.04039v2 [cond-mat.quant-gas]

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The causes of neuronal dysfunction and degeneration in Alzheimer's disease (AD) are not fully understood, but increased production of neurotoxic forms of amyloid beta-peptide-42 (Abeta42) seems of major importance. Large extracellular deposits of aggregated Abeta42 (plaques) is a diagnostic feature of AD, but Abeta42 may be particularly cytotoxic when it accumulates inside neurons. The factors that may promote the intracellular accumulation of Abeta42 in AD are unknown, but recent findings suggest that individuals with elevated homocysteine levels are at increased risk for AD. We show that homocysteic acid (HA), an oxidized metabolite of homocysteine, induces intraneuronal accumulation of a Abeta42 that is associated with cytotoxicity. The neurotoxicity of HA can be attenuated by an inhibitor of gamma-secretase, the enzyme activity that generates Abeta42, suggesting a key role for intracellular Abeta42 accumulation in the neurotoxic action of HA. Concentrations of HA in cerebrospinal fluid (CSF) were similar in AD and control subjects. CSF homocysteine levels were elevated significantly in AD patients, however, and homocysteine exacerbated HA-induced neurotoxicity, suggesting a role for HA in the pathogenic action of elevated homocysteine levels in AD. These findings suggest that the intracellular accumulation of Abeta42 plays a role in the neurotoxic action of HA, and suggest a potential therapeutic benefit of agents that modify the production and neurotoxic actions of HA and homocysteine.

A single Weyl fermion, which is prohibited in static lattice systems by the Nielsen-Ninomiya theorem, is shown to be realized in a periodically driven three-dimensional lattice system with a topologically nontrivial Floquet unitary operator, manifesting the chiral magnetic effect. We give a topological classification of Floquet unitary operators in the Altland-Zirnbauer symmetry classes for all dimensions, and use it to predict that all gapless surface states of topological insulators and superconductors can emerge in bulk quasienergy spectra in Floquet systems.In 1981, Nielsen and Ninomiya proved that a single Weyl fermion cannot be realized in lattice systems [1,2]. This theorem places a fundamental constraint on band structures due to the topology of the Brillouin zone. Weyl fermions have recently played a key role in crossfertilizing ideas from high-energy physics and condensedmatter physics. A prime example is the prediction of Weyl semimetals [3,4], where the low-energy effective field theory of Weyl fermions predicts novel electromagnetic responses originating from the chiral anomaly [5][6][7][8]. In particular, the observations of the surface Fermi arc [9][10][11][12][13][14][15] and anomalous transport [16][17][18][19] have aroused considerable interest. However, if a system is defined on a lattice and thus anomaly-free, the Nielsen-Ninomiya theorem dictates that a Weyl fermion be accompanied by its partner with opposite chirality. By the same token, an anomaly-induced response known as the chiral magnetic effect (CME) [20] does not occur in equilibrium [21], and numerous attempts to circumvent this difficulty have been made [22][23][24][25][26][27][28][29].In this Letter, we demonstrate that a single Weyl fermion can be realized on a periodically driven lattice, thereby overcoming the above limitations. In periodically driven (Floquet) systems, the unitary time-evolution operator over one period defines an effective Hamiltonian and the associated quasienergies [30]. Despite the apparent similarity to static systems, Floquet systems enable the realization of exotic phases that cannot be achieved in equilibrium, such as anomalous topological insulators [31,32] and time crystals [33,34]. The key idea of our proposal is an emerging topological structure in unitary operators associated with the periodicity of quasienergies [31]. We here show that a driving protocol for a three-dimensional (3D) Thouless pump [31,35] given by a topological Floquet unitary operation realizes a single Weyl fermion in a 3D lattice system, thereby providing a platform to observe the CME. We demonstrate that chiral transport emerges under a topological 3D Floquet drive with an applied synthetic magnetic field, leading to a Floquet realization of the CME. Our proposal can be implemented by using ultracold atomic gases, where the Thouless pump has been realized experimentally [36,37]. Furthermore, by exploiting the correspondence between anomalous gapless spectra and topological unitary operators, we provide a topological classificat...

In quantum magnetism, the virtual exchange of particles mediates an interaction between spins. Here we show that an inelastic Hubbard interaction fundamentally alters the magnetism of the Hubbard model due to dissipation in spin-exchange processes, leading to sign reversal of magnetic correlations in dissipative quantum dynamics. This mechanism is applicable to both fermionic and bosonic Mott insulators, and can naturally be realized with ultracold atoms undergoing two-body inelastic collisions. The dynamical reversal of magnetic correlations can be detected by using a double-well optical lattice or quantum-gas microscopy, the latter of which enhances the signal of the magnetic correlations owing to spin-charge separation in one-dimensional systems. Our results open a new avenue toward controlling quantum dissipative many-body states.

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