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arXiv:2301.09464 · Physica Scripta

M -neighbor approximation in one-qubit state transfer along zigzag and alternating spin-1/2 chains

Edward B. Fel’dman, Alexander Ivanovich Zenchuk

Published Jul 26, 2022• 3 citations
arXivHTMLPDF

Abstract

Abstract We consider the M -neighbor approximation in the problem of one-qubit pure state transfer along the N -node zigzag and alternating spin chains governed by the XXZ -Hamiltonian with the dipole-dipole interaction. We show that always M > 1, i.e., the nearest neighbor approximation is not applicable to such interaction. Moreover, only all-node interaction ( M = N − 1) properly describes the dynamics in the alternating chain. We reveal the region in the parameter space characterizing the chain geometry and orientation which provide the high-probability state-transfer. The optimal state-transfer probability and appropriate time instant for the zigzag and alternating chains are compared.

DOI
10.1088/1402-4896/ac8456

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Abstract We consider the M -neighbor approximation in the problem of one-qubit pure state transfer along the N -node zigzag and alternating spin chains governed by the XXZ -Hamiltonian with the dipole-dipole interaction. We show that always M > 1, i.e., the nearest neighbor approximation is not applicable to such interaction. Moreover, only all-node interaction ( M = N − 1) properly describes the dynamics in the alternating chain. We reveal the region in the parameter space characterizing the chain geometry and orientation which provide the high-probability state-transfer. The optimal state-transfer probability and appropriate time instant for the zigzag and alternating chains are compared.
This article is devoted to the development of analytical and numerical approaches to the problem of the end-to-end quantum state transfer along the spin-1/2 chain using two methods: (a) a homogeneous spin chain with week end bonds and equal Larmor frequencies and (b) a homogeneous spin chain with end Larmor frequencies different from inner ones. A tridiagonal matrix representation of the XY\mathit{XY}XY Hamiltonian with nearest neighbor interactions relevant to the quantum state transfer is exactly diagonalized for a combination of the preceding two methods. In order to take into account interactions of the remote spins, we used numerical simulations of the quantum state transfer in 10-node chains. We compare the state transfer times obtained using the two preceding methods for chains governed by the both XY\mathit{XY}XY and XXZ\mathit{XXZ}XXZ Hamiltonians and using both nearest neighbor and all-node interactions.
Most of the existing dynamical studies in one dimension on magnetic insulators have considered the simplest spin models with nearest-neighbor interactions. In real systems, however, it is possible that longer range interactions are not entirely negligible. It is expected that the inclusion of next-nearest-neighbor interactions between spins in one-dimensional spin models will introduce a multitude of new frequencies in addition to the ones already present in the dynamics that arises due to nearest-neighbor interactions. We first present an exact solution for the dynamical xx-spin-pair correlations in an Ising chain with both nearest- and next-nearest-neighbor interactions to confirm our expectation. We next show, via an approximate analytical calculation, that the dynamical zz-spin-pair correlations in the next-nearest-neighbor transverse Ising chain when plotted as a function of time is noticeably different with respect to the exactly solvable nearest-neighbor transverse Ising chain at T\ensuremath{\rightarrow}\ensuremath{\infty} when the next-nearest-neighbor interaction is \ensuremath{\gtrsim}1/2 of the magnitude of the nearest-neighbor interaction. The effects could be fairly subtle in the time domain representation and in the spectral function when these additional interactions are weak (i.e., 1/2 of the nearest-neighbor interaction magnitude). The general conclusions reached in this work are expected to be valid for other simple quantum spin models such as the XY and XXZ models in one dimension. \textcopyright{} 1996 The American Physical Society.
We investigate various properties of a linear chain of qubits coupled throughthe dipole-dipole interaction. Most of the analysis is performed in the nearest-neighbor approximation. The Hamiltonian is ¯rst diagonalized, and we ex-plore some of the mathematical properties of the eigenstates. The patternof radiation emission from the single-excitation states is given, along withthe demonstration that most of these single-excitation states are subradiant,making them useful in applications such as quantum information storage andprocessing. The entanglement dynamics of the chain is also investigated,mainly showing how very long chains lose initial concurrence, as opposed toshort chains which do not.We conclude with an investigation into trying to move beyond the nearest-neighbor approximation, and derive the characteristic polynomial of theHamiltonian eigenvalue equation in analytic form, and use it to derive apower series approximation for the energy eigenvalues.
A system with externally polarized dipole molecules at half-filling moving along a one-dimensional zigzag chain is studied, including ground-state phase diagrams. The dipoles are oriented in-plane. Together with the geometry of the chain, this gives rise to a bond-alternating nearest-neighbor interaction due to simultaneous attractive and repulsive interactions. By tuning the ratio between the nearest-neighbor interaction and hopping, various phases can be accessed by controlling the polarization angle. In the ultrastrong coupling limit, the system simplifies to a frustrated extended axial Ising model. For the small coupling limit, qualitative discussion of the ordering behavior using effective field theory arguments is provided. We show that when the chain angle is small, the system mostly exhibits BKT-type phase transitions, whereasa large chain angle would drive the system into a gapped (Ising) dimerized phase, where the hopping strength is closely related to the orientation of dimerized pairs.
We extend the picture of a transfer of nuclear spin-1/2 polarization along a homogeneous one-dimensional chain with the XY Hamiltonian to the inhomogeneous chain with alternating nearest neighbor couplings and alternating Larmor frequencies. To this end, we exactly calculate the spectrum of the spin-1/2 XY Hamiltonian of the alternating chain with an odd number of sites. The exact spectrum of the XY Hamiltonian is also applied to study the multiple quantum (MQ) NMR dynamics of the alternating spin-1/2 chain. MQ NMR spectra are shown to have the MQ coherences of zero and ± second orders just as in the case of a homogeneous chain. The intensities of the MQ coherences are calculated.
A method for exactly diagonalizing the XY Hamiltonian of an alternating open chain of spins s = 1/2 has been proposed on the basis of the Jordan-Wigner transformation and analysis of the dynamics of spinless fermions. The multiple-quantum spin dynamics of alternating open chains at high temperatures has been analyzed and the intensities of multiple-quantum coherences have been calculated. The problem of the transfer of a quantum state from one end of the alternating chain to the other is studied. It has been shown that the ideal transfer of qubits is possible in alternating chains with a larger number of spins than that in homogeneous chains.