Topological defects and excitations in spin ladders

We investigate the low-lying excitation of the antiferromagnetic zigzag spin ladder with M\"obius boundary condition. Using the Lanczos and Householder diagonalization methods, we calculate the excitation spectrum of the zigzag ladder in the momentum space. We then show that the topological defect generated by the M\"obius boundary provides the clear evidence of the single-spinon excitation. On the basis of the obtained single-spinon dispersion curve, we analyze the two-spinon scattering states under the usual periodic boundary condition. We further discuss the interaction effect between the spinons, and the connection to the cusp singularity in the magnetization process.We investigate the low-lying excitation of the antiferromagnetic zigzag spin ladder with M\"obius boundary condition. Using the Lanczos and Householder diagonalization methods, we calculate the excitation spectrum of the zigzag ladder in the momentum space. We then show that the topological defect generated by the M\"obius boundary provides the clear evidence of the single-spinon excitation. On the basis of the obtained single-spinon dispersion curve, we analyze the two-spinon scattering states under the usual periodic boundary condition. We further discuss the interaction effect between the spinons, and the connection to the cusp singularity in the magnetization process.

arXiv:cond-mat/0104101Physical review. B, Condensed matterNov 13, 200118 citations

Topological phases and quenches in spin-ladder systems

Smitha Vishveshwara, Wade DeGottardi, Diptiman Sen

APSMar 1, 20110 citations

Magnetic excitations in spin ladders with intrinsic impurities

H.-J. Mikeska, U Neugebauer

Physica B Condensed MatterDec 1, 19970 citations

Locally tunable disorder and entanglement in the one-dimensional plaquette orbital model

Wojciech Brzezicki, Andrzej M. Oleś

We introduce a one-dimensional plaquette orbital model with a topology of a ladder and alternating interactions between $x$ and $z$ pseudospin components both along the ladder legs and on the rungs. We show by an exact transformation that it is equivalent to an effective spin model in a magnetic field, with spin dimers that replace plaquettes and are coupled along the chain by three-spin interactions in the Hilbert space reduced by a factor of 2. Using perturbative treatment and mean-field approaches with dimer correlations we study the ground state spin configuration and its defects in the lowest excited states. By the exact diagonalization approach we establish that the quantum effects are of purely short-range nature in the model and we find estimated values of the ground state energy and the gap in the thermodynamic limit from the system sizes up to $L=12$ dimers. Finally, we study a class of excited states with classical-like defects accumulated in the central region of the chain to find that in this region the quantum entanglement measured by the mutual information of neighboring dimers is locally increased and coincides with disorder and frustration. Such islands of entanglement in an otherwise rather classical system may be of interest in the context of quantum computing devices.We introduce a one-dimensional plaquette orbital model with a topology of a ladder and alternating interactions between $x$ and $z$ pseudospin components both along the ladder legs and on the rungs. We show by an exact transformation that it is equivalent to an effective spin model in a magnetic field, with spin dimers that replace plaquettes and are coupled along the chain by three-spin interactions in the Hilbert space reduced by a factor of 2. Using perturbative treatment and mean-field approaches with dimer correlations we study the ground state spin configuration and its defects in the lowest excited states. By the exact diagonalization approach we establish that the quantum effects are of purely short-range nature in the model and we find estimated values of the ground state energy and the gap in the thermodynamic limit from the system sizes up to $L=12$ dimers. Finally, we study a class of excited states with classical-like defects accumulated in the central region of the chain to find that in this region the quantum entanglement measured by the mutual information of neighboring dimers is locally increased and coincides with disorder and frustration. Such islands of entanglement in an otherwise rather classical system may be of interest in the context of quantum computing devices.

arXiv:1405.1401Physical Review BJul 31, 20148 citations

Observation of a topological defect state in the quantum Rabi model

Kyungmin Lee, Jiyong Kang, Sunkyu Yu +3 more

Synthetic lattices built from hybrid qubit-oscillator systems provide a platform for exploring topology, with multiple physical degrees of freedom enabling control over lattice geometry. A single spin-oscillator pair, described by the quantum Rabi model, provides a minimal system supporting a topological defect state on a lattice formed from the oscillator's infinite ladder of number states. However, the realization of the defect state and its robustness remain experimentally unexplored. Here we realize a topological defect state of the quantum Rabi model in a single trapped $^{171}\mathrm{Yb}^{+}$ ion. As a coupling phase varies, reconstructed phase-space distributions yield centroid trajectories with windings of one and zero in two regimes, linking discrete-lattice topology to the geometry of the oscillator's continuous position-momentum space. The measured spin response to drive-amplitude modulation relates the stability of spin polarization to energy gaps and allowed transitions. Together, these results establish a minimal quantum system for realizing and probing topological defect states.Synthetic lattices built from hybrid qubit-oscillator systems provide a platform for exploring topology, with multiple physical degrees of freedom enabling control over lattice geometry. A single spin-oscillator pair, described by the quantum Rabi model, provides a minimal system supporting a topological defect state on a lattice formed from the oscillator's infinite ladder of number states. However, the realization of the defect state and its robustness remain experimentally unexplored. Here we realize a topological defect state of the quantum Rabi model in a single trapped $^{171}\mathrm{Yb}^{+}$ ion. As a coupling phase varies, reconstructed phase-space distributions yield centroid trajectories with windings of one and zero in two regimes, linking discrete-lattice topology to the geometry of the oscillator's continuous position-momentum space. The measured spin response to drive-amplitude modulation relates the stability of spin polarization to energy gaps and allowed transitions. Together, these results establish a minimal quantum system for realizing and probing topological defect states.

quant-pharXiv:2609.34389Sep 29, 20260 citations

We introduce a one-dimensional plaquette orbital model with a topology of a ladder and alternating interactions between

x

and

z

pseudospin components both along the ladder legs and on the rungs. We show by an exact transformation that it is equivalent to an effective spin model in a magnetic field, with spin dimers that replace plaquettes and are coupled along the chain by three-spin interactions in the Hilbert space reduced by a factor of 2. Using perturbative treatment and mean-field approaches with dimer correlations we study the ground state spin configuration and its defects in the lowest excited states. By the exact diagonalization approach we establish that the quantum effects are of purely short-range nature in the model and we find estimated values of the ground state energy and the gap in the thermodynamic limit from the system sizes up to

L=12

dimers. Finally, we study a class of excited states with classical-like defects accumulated in the central region of the chain to find that in this region the quantum entanglement measured by the mutual information of neighboring dimers is locally increased and coincides with disorder and frustration. Such islands of entanglement in an otherwise rather classical system may be of interest in the context of quantum computing devices.

^{171}\mathrm{Yb}^{+}

ion. As a coupling phase varies, reconstructed phase-space distributions yield centroid trajectories with windings of one and zero in two regimes, linking discrete-lattice topology to the geometry of the oscillator's continuous position-momentum space. The measured spin response to drive-amplitude modulation relates the stability of spin polarization to energy gaps and allowed transitions. Together, these results establish a minimal quantum system for realizing and probing topological defect states.