Observation of magnon bound states in the long-range, anisotropic Heisenberg model

Over the recent years coherent, time-periodic modulation has been established as a versatile tool for realizing novel Hamiltonians. Using this approach, known as Floquet engineering, we experimentally realize a long-ranged, anisotropic Heisenberg model with tunable interactions in a trapped ion quantum simulator. We demonstrate that the spectrum of the model contains not only single magnon excitations but also composite magnon bound states. For the long-range interactions with the experimentally realized power-law exponent, the group velocity of magnons is unbounded. Nonetheless, for sufficiently strong interactions we observe bound states of these unconventional magnons which possess a non-diverging group velocity. By measuring the configurational mutual information between two disjoint intervals, we demonstrate the implications of the bound state formation on the entanglement dynamics of the system. Our observations provide key insights into the peculiar role of composite excitations in the non-equilibrium dynamics of quantum many-body systems

Deconfined Quantum Criticality in the long-range, anisotropic Heisenberg Chain

<p>Deconfined quantum criticality describes continuous phase transitions that are not captured by the Landau-Ginzburg paradigm. Here, we investigate deconfined quantum critical points in the long-range, anisotropic Heisenberg chain. With matrix product state simulations, we show that the model undergoes a continuous phase transition from a valence bond solid to an antiferromagnet. We extract the critical exponents of the transition and connect them to an effective field theory obtained from bosonization techniques. We show that beyond stabilizing the valance bond order, the  long-range interactions are irrelevant and the transition is well described by a double frequency sine-Gordon model. We propose how to realize and probe deconfined quantum criticality in our model with trapped-ion quantum simulators.</p&gt

Deconfined quantum criticality in the long-range, anisotropic Heisenberg chain

Deconfined quantum criticality describes continuous phase transitions that are not captured by the Landau-Ginzburg paradigm. Here, we investigate deconfined quantum critical points in the long-range, anisotropic Heisenberg chain. With matrix product state simulations, we show that the model undergoes a continuous phase transition from a valence bond solid to an antiferromagnet. We extract the critical exponents of the transition and connect them to an effective field theory obtained from bosonization techniques. We show that beyond stabilizing the valance bond order, the long-range interactions are irrelevant and the transition is well described by a double frequency sine-Gordon model. We propose how to realize and probe deconfined quantum criticality in our model with trapped-ion quantum simulators

Signatures of Confinement in Raman Spectroscopy of Ising Spin Chains

<p>Confinement of excitations is usually considered as a phenomenon of high-energy physics. How-<br> ever, over the recent years, related effects have been discussed in condensed matter settings as well.<br> A paradigmatic example is the formation of mesonic bound states in spin chains with linear con-<br> finement between domain walls. A prominent candidate material is the quasi-one dimensional Ising<br> magnet CoNb2O6 for which mesonic bound states have been detected by neutron scattering exper-<br> iments. In this work, we study the Raman response of a twisted Kitaev chain in the presence of a<br> magnetic field as a minimal model for confinement in CoNb2O6 and compute the response within<br> the theory by Fleury and Loudon. We show that the bound states directly manifest themselves as<br> sharp peaks in the Raman response, which we numerically compute using Matrix Product States.<br> We find that the main features of the spectrum can be well understood by a trial wave-function,<br> which contains a few solitonic excitations only. Moreover, when approaching the critical regime<br> Raman spectroscopy can be used to directly detect Ising quantum criticality via the emergence of<br> the famous E8 symmetry in the response spectrum.</p&gt

Characterizing Topological Excitations of a Long-Range Heisenberg Model with Trapped Ions

Realizing and characterizing interacting topological phases in synthetic quantum systems is a formidable challenge. Here, we propose a Floquet protocol to realize the antiferromagnetic Heisenberg model with power-law decaying interactions. Based on analytical and numerical arguments, we show that this model features a quantum phase transition from a liquid to a valence bond solid that spontaneously breaks lattice translational symmetry and is reminiscent of the Majumdar-Ghosh state. The different phases can be probed dynamically by measuring the evolution of a fully dimerized state. We moreover introduce an interferometric protocol to characterize the topological excitations and the bulk topological invariants of the interacting many-body system.Comment: 13 pages, 12 figures, revised version contains significantly extended discussion of the implementation of the Zak protoco

N(G)-Acylated aminothiazolylpropylguanidines as potent and selective histamine H2 receptor agonists

The bioisosteric replacement of the guanidino group in arpromidine-like histamine H2 receptor (H2R) agonists by an acylguanidine moiety is a useful approach to obtain potent H2R agonists with improved oral bioavailability and penetration across the blood brain barrier. Unfortunately, the selectivity of such N(G)-acylated imidazolylpropyl-guanidines for the H2R is poor, in particular versus histamine H3 (H3R) and H4 receptors (H4R). This drawback appears to depend on the "privileged" imidazolylpropylguanidine structure. The 2-amino-4-methylthiazol-5-yl moiety is a bioisostere of the imidazole ring in the moderately potent H2R selective histamine analogue amthamine. This approach was successfully applied to acylguanidine-type H2R agonists. The aminothiazoles are nearly equipotent with the corresponding imidazoles as H2R agonists. Compared to histamine, the potency is increased up to 40-fold on the guinea pig right atrium and up to 125- and 280-fold, respectively, in GTPase assays at human and guinea pig H2R-GsαS fusion proteins expressed in Sf9 insect cells. Docking studies on H2R models support the hypothesis that 2-aminothiazolyl and imidazolyl derivatives interact with H2Rs as bioisosteres. In contrast to the imidazoles, the aminothiazoles are devoid of agonistic or relevant antagonistic effects on H1, H3 and H4 receptors. Moreover, unlike amthamine, the 4-methyl group does not significantly contribute to the H2R agonism of N(G)-acylated 2-amino-4-methylthiazol-5-ylpropylguanidines

Chiral N(G)-acylated hetarylpropylguanidine-type histamine H2 receptor agonists do not show significant stereoselectivity

A set of chiral imidazolylpropylguanidines and 2-aminothiazolylpropylguanidines bearing N(G)-3-phenyl- or N(G)-3-cyclohexylbutanoyl residues was synthesized and investigated for histamine H2 receptor (H2R) agonism (guinea pig (gp) right atrium, GTPase assay on recombinant gp and human (h) H2R) and for hH2R selectivity compared to hH1R, hH3R and hH4R. In contrast to previous studies on arpromidine derivatives, the present investigation of acylguanidine-type compounds revealed only very low eudismic ratios (1.1 – 3.2), indicating the stereochemistry of the acyl moiety to play only a minor role in this series of H2R agonists

The bivalent ligand approach leads to highly potent and selective acylguanidine-type histamine H2 receptor agonists

Bivalent histamine H2 receptor (H2R) agonists were synthesized by connecting pharmacophoric 3-(2-amino-4-methylthiazol-5-yl)-, 3-(2-aminothiazol-5-yl)-, 3-(imidazol-4-yl)- or 3-(1,2,4-triazol-5-yl)-propylguanidine moieties by NG-acylation with alkanedioic acids of various chain lengths. The compounds were investigated for H2R agonism in GTPase and [35S]GTPγS binding assays at guinea pig (gp) and human (h) H2R-GsαS fusion proteins including various H2R mutants, at the isolated gp right atrium, and in GTPase assays for activity on recombinant H1, H3 and H4 receptors. The bivalent ligands are H2R partial or full agonists, up to two orders of magnitude more potent than monovalent acylguanidines and, with octanedioyl or decanedioyl spacers, up to 4000 times more potent than histamine at the gpH2R. In contrast to their imidazole analogs, the aminothiazoles are highly selective for H2R vs. other HR subtypes. Compounds with (theoretically) sufficient spacer length (20 CH2 groups) to simultaneously occupy two orthosteric binding sites in H2R dimers are nearly inactive, whereas highest potency resides in compounds with considerably shorter spacers. Thus, there is no evidence for interaction with H2R dimers. The high agonistic potency may rather result from interaction with an accessory binding site at the same receptor protomer

Molecular and cellular analysis of human histamine receptor subtypes

The human histamine receptors hH1R and hH2R constitute important drug targets, and hH3R and hH4R have substantial potential in this area. Considering the species-specificity of pharmacology of HxR orthologs, it is important to analyze hHxRs. Here, we summarize current knowledge of hHxRs endogenously expressed in human cells and hHxRs recombinantly expressed in mammalian and insect cells. We present the advantages and disadvantages of the various systems. We also discuss problems associated with the use of hHxRs antibodies, an issue of general relevance for G-protein-coupled receptors. There is much greater overlap in activity of “selective” ligands for other hHxRs than the cognate receptor subtype than generally appreciated. Studies with native and recombinant systems support the concept of ligand-specific receptor conformations, encompassing agonists and antagonists. It is emerging that for characterization of hHxR ligands, one cannot rely on a single test system and a single parameter. Rather, multiple systems and parameters have to be studied. Although such studies are time-consuming and expensive, ultimately, they will increase drug safety and efficacy