Masaya Nakagawa 교수

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 nonunitarity and produce a quantum phase transitio

A one-dimensional dissipative Hubbard model with two-body loss is shown to be exactly solvable. We obtain an exact eigenspectrum of a Liouvillian superoperator by employing a non-Hermitian extension of the Bethe-ansatz method. We find steady states, the Liouvillian gap, and an exceptional point that is accompanied by the divergence of the correlation length. A dissipative version of spin-charge separation induced by the quantum Zeno effect is also demonstrated. Our result presents a new class of

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

We demonstrate that laser excitations can coherently induce a novel Kondo effect in ultracold atoms in optical lattices. Using a model of alkaline-earth fermions with two orbitals, it is shown that the optically coupled two internal states are dynamically entangled to form the Kondo-singlet state, overcoming the heating effect due to the irradiation. Furthermore, a lack of SU(N) symmetry in the optical coupling provides a peculiar feature in the Kondo effect, which results in spin-selective reno

We elucidate the mechanism for instability of topological Thouless pumping in strongly interacting systems from a viewpoint of symmetry-protected topological phases. If the protecting symmetries of the underlying topological phases change between noninteracting fermions and a bosonic system in the strong coupling limit, the symmetry-protection argument enforces a gap closing and thereby predicts a breakdown of the topological pumping. We also demonstrate that, even in the weakly interacting regi

A universal feature of topological insulators is that they cannot be adiabatically connected to an atomic limit, where individual lattice sites are completely decoupled. This property is intimately related to a topological obstruction to constructing a localized Wannier function from Bloch states of an insulator. Here, we generalize this characterization of topological phases toward periodically driven systems. We show that nontrivial connectivity of hybrid Wannier centers in momentum space and

Variapeptin and citropeptin were found as novel hexadepsipeptide antibiotics produced by Streptomyces variabilis and Streptomyces flavidovirens, respectively. Their structures were elucidated by NMR spectral analysis including a variety of 2D techniques. Variapeptin and citropeptin are structurally realted to azinothricin and A83586C, respectively.

The metal content of diaphragm, gastrocnemius, ventricle, and bladder muscles in genetically obese diabetic KK-CAy and alloxan-diabetic ddY mice was compared with that in prediabetic KK-CAy and normal ddY mice, because the muscles of the diabetic KK-CAy mice had morphological abnormalities, such as atrophy, disappearance of Z-band, disturbed myofibrils and swollen sarcoplasmic reticulum. The amounts of calcium (Ca) in gastrocnemius, ventricle and bladder muscles from the prediabetic KK-CAy mice

A new antitumor antibiotic, designated AL081, was obtained from the culture filtrate of an actinomycete identified as Streptomyces gannmycicus, and found to be identical with viridenomycin by direct comparison. The structure of the antibiotic was determined by NMR spectral analysis including a variety of two-dimensional techniques to be a novel 24-membered macrocyclic polyene lactam. Viridenomycin prolonged the survival periods of mice bearing P388 leukemia and B16 melanoma cells.

Carotenoid glycosides are considered to protect cells against photooxidative damage by activated oxygen plus visible light,l) or to stabilize a membraneenvironment, similarly to the function of sterols in eucaryotic cells.2) Recently the genes required for the biosynthesis of this

As part of our biosynthetic studies on anthracycline antibiotics, we attempted to develop a cloning system using a cinerubin-producing organism isolated in our laboratory Streptomyces violaceochromogenes as a host. This strain was found to be transformed by the plasmid, pIJ7021). As a first step to clone the structural gene controlling the cinerubin biosynthesis, we isolated cinerubin-negative mutants of S. violaceochromogenes. Among these mutants the strain C73 was found to produce a new anthra

Topological pumping, which was originally proposed by Thouless, is a beautiful manifestation of quantum effects in transport phenomena. Thouless's topological pumping is characterized by the topology of Bloch states in the space of momentum and time, and can be viewed as a dynamical analog of the integer quantum Hall effect of noninteracting fermions. Here, the authors propose a systematic procedure to construct nontrivial classes of topological pumping from strongly correlated quantum Hall stat

Recently, concepts of topological phases of matter are extended to nonequilibrium systems, especially periodically driven systems. In this paper, we construct an example which shows nonequilibrium topological phase transitions using ultracold fermions in optical lattices. We show that the Rabi oscillation has the possibility to induce nonequilibrium topological phases which are classified into time-reversal-invariant topological insulators for a two-orbital model of alkaline-earth-metal atoms. F