Floquet dynamical quantum phase transitions in transverse XY spin chains under periodic kickings

Floquet dynamical quantum phase transitions(DQPTs),which are nonanalytic phenomena recuring periodically in time-periodic driven quantum many-body systems,have been widely studied in recent years.In this article,the Floquet DQPTs in transverse XY spin chains under the modulation ofδ-function periodic kickings are investigated.We analytically solve the system,and by considering the eigenstate as well as the ground state as the initial state of the Floquet dynamics,we study the corresponding multiple Floquet DQPTs emerged in the micromotion with different kicking moments.The rate function of return amplitude,the Pancharatnam geometric phase and the dynamical topological order parameter are calculated,which consistently verify the emergence of Floquet DQPTs in the system.

Synthesis, structure, and properties of Ba9Co3Se(15) with one-dimensional spin chains

A new compound with one-dimensional spin chains, Ba9Co3Se(15), was synthesized under high pressure and high temperature conditions and systematically characterized via structural, transport and magnetic measurements. Ba9Co3Se(15) crystallizes in a hexagonal structure with the space group P-6c2(No. 188) and lattice constants of a = b = 9.6765 ? and c = 18.9562 ?. The structure consists of trimeric face-sharing octahedral CoSe6 chains, which are arranged in a triangular lattice in the ab-plane and separated by Ba atoms. The distance of the nearest neighbor of CoSe6 chains is very large, given by the lattice constant a = 9.6765 ?. The Weiss temperature Tθ associated with the intra-chain coupling strength is about -346 K. However, no long-range magnetic order but a spin glass transition at ~ 3 K has been observed. Our results indicate that the spin glass behavior in Ba9Co3Se(15) mainly arises from the magnetic frustration due to the geometrically frustrated triangular lattice.

The Physical Property of Susceptibility for One-Dimensional Ferrimagnetic Chain with Alternating Spins 1 and 1/2 in Finite Magnetic Field

We further calculate the dependence of xT on T in high magnetic fields,where X denotes susceptibility and T is temperature,using our previous research work - Green function's decoupling approximate approach,for the one-dimensional ferrimagnetic chain with alternating spins 1 and 1/2.We find a linear correlation in certain range of magnetic field between the temperature of xT maximum and the magnetic field.Moreover,we simply analyze its physical meaning by our approach.

Exact surface energy and elementary excitations of the XXX spin-1/2 chain with arbitrary non-diagonal boundary fields

We study the physical properties of the XXX spin-1/2 chain with arbitrary non-diagonal boundary fields. By using a combination of numerical analysis and analytical method, we obtain the surface energy and elementary excitations of the model. It shows that the contributions of the two boundary fields to the surface energy are additive. We also find that there exists a kind of excitations related to the boundary string.

Stability of the Konjac Glucomannan Topological Chain Based on Quantum Spin Model

In this paper we investigated the stability of konjac glucomnnan（KGM） chain hydrogen networks based on the quantum spin model. Dissipative particle dynamics method was applied in the structure simulation of KGM. The results reveled that acetyl residues of KGM were bonded with water molecules in aqueous solutions. Increasing the hydrogen bond formation decreases the energy in acetyl system. The expect-valuation of the thermal state with respect to the Hamiltonian is negative. Hence, the total energy of konjac glucomnnan chain with the acetyl groups decreases, which indicates the increasing stability of konjac glucomnnan chain. Our approach could provide a new insight into the investigation on the stability of konjac glucomnnan chain.

Quantum Communication in Spin Chain with Multiple Spin Exchange Interaction

The transmission of quantum states in the anisotropic Heisenberg XXZ chain model with three-spin exchange interaction is studied. The average fidelity is used to evaluate the state transfer. It is found that quantum communication can be enhanced by the anisotropic coupling and multiple spin interaction. Such spin model can reduce the time required for the perfect state transmission where the fidelity is unity. The maximally entangled Bell states can be generated and separated from the whole quantum systems.

Quantum correlations dynamics of three-qubit states coupled to an XY spin chain: Role of coupling strengths

We investigate the prominent impacts of coupling strengths on the evolution of entanglement and quantum discord for a three-qubit system coupled to an XY spin-chain environment. In the case of a pure W state, more robust, even larger nonzero quantum correlations can be obtained by tailoring the coupling strengths between the qubits and the environment. For a mixed state consisting of the GHZ and W states, the dynamics of entanglement and quantum discord can characterize the critical point of quantum phase transition. Remarkably, a large nonzero quantum discord is generally retained, while the nonzero entanglement can only be obtained as the system-environment coupling satisfies certain conditions. We also find that the impact of each qubit＇s coupling strength on the quantum correlation dynamics strongly depends on the variation schemes of the system-environment couplings.

Study of Decoherence of Elementary Gates Implemented in a Chain of Few Nuclear Spins Quantum Computer Model

We study the phenomenon of decoherence during the operation of one qubit transformation, controlled-not (CNOT) and controlled-controlled-not (C2NOT) quantum gates in a quantum computer model formed by a linear chain of three nuclear spins system. We make this study with different type of environments, and we determine the associated decoherence time as a function of the dissipative parameter. We found that the dissipation parameter to get a well defined quantum gates (without significant decoherence) must be within the range of . We also study the behavior of the purity parameter for these gates and different environments and found linear or quadratic decays of this parameter depending on the type of environments.

Controlling Quantum State Transfer in Spin Chain with Confined Field

As a demonstration of the spectrum-parity matching condition （SPMC） for quantum state transfer, we investigate the propagation of single-magnon state in the Heisenberg chain in the confined external tangent magnetic field analytically and numerically. It shows that the initial Gaussian wave packet can be retrieved at the counterpart location near-perfectly over a longer distance if the dispersion relation of the system meets the SPMC approximately.

Spin transport in a chain of polygonal quantum rings with Dresselhaus spin-orbit coupling

Using a transfer matrix method, we investigate spin transport through a chain of polygonal rings with Dresselhaus spin-orbit coupling（DSOC）. The spin conductance is dependent on the number of sides in the polygons. When DSOC is considered in a chain which also has Rashba spin-orbit coupling（RSOC） of the same magnitude, the total conductance is the same as that for the same chain with no SOC. However, when the two types of SOC have different values, there results a unique anisotropic conductance.

Dynamical signatures of the one-dimensional deconfined quantum critical point

We study the critical scaling and dynamical signatures of fractionalized excitations at two different deconfined quantum critical points(DQCPs)in an S=1/2 spin chain using the time evolution of infinite matrix product states.The scaling of the correlation functions and the dispersion of the conserved current correlations explicitly show the emergence of enhanced continuous symmetries at these DQCPs.The dynamical structure factors in several different channels reveal the development of deconfined fractionalized excitations at the DQCPs.Furthermore,we find an effective spin-charge separation at the DQCP between the ferromagnetic(FM)and valence bond solid(VBS)phases,and identify two continua associated with different types of fractionalized excitations at the DQCP between the X-direction and Z-direction FM phases.Our findings not only provide direct evidence for the DQCP in one dimension but also shed light on exploring the DQCP in higher dimensions.

Quantum Monte Carlo Study of Frustrated Spin Chain under External Field

In this paper a stochastic series expansion quantum Monte Carlo algorithm is used to study a frustratedspin chain with diagonal next-nearest-neighbor interactions.The detailed balance conditions are carefully analyzed toimprove the efficiency of simulation process.As an application of this algothrim,the total magnetization,the staticstructure factor and spin-stiffness are calculated for a certain set of system parameters as a function of external fieldstrength.

Exact solution of an integrable quantum spin chain with competing interactions

We construct an integrable quantum spin chain that includes the nearest-neighbor,next-nearest-neighbor,chiral threespin couplings,Dzyloshinsky–Moriya interactions and unparallel boundary magnetic fields.Although the interactions in bulk materials are isotropic,the spins nearby the boundary fields are polarized,which induce the anisotropic exchanging interactions of the first and last bonds.The U(1)symmetry of the system is broken because of the off-diagonal boundary reflections.Using the off-diagonal Bethe ansatz,we obtain an exact solution to the system.The inhomogeneous T–Q relation and Bethe ansatz equations are given explicitly.We also calculate the ground state energy.The method given in this paper provides a general way to construct new integrable models with certain interesting interactions.

Role of the spin anisotropy of the interchain interaction in weakly coupled antiferromagnetic Heisenberg chains

In quasi-one-dimensional(q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic(AFM) compound YbAlO3, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations,and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave(LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.

Macroscopic Quantum Coherence in an Antiferromagnetic Spin Chain with Biaxial Anisotropy

Instanton configurations of （1＋1）-dimensions in an antiferromagnetic biaxial-anisotropy-spin-chain are obtained explicitly in the strong anisotropy limit, which interpolate between degenerate equilibrium orientations of the Neel vector along easy axis and are seen to be responsible for quantum tunneling. Macroscopic quantum coherence of the domain walls is demonstrated in terms of the instantons.

Perfect Entanglement Transport in Quantum Spin Chain Systems

We propose a mechanism for perfect entanglement transport in anti-ferromagnetic (AFM) quantum spin chain systems with modulated exchange coupling and also for the modulation of on-site magnetic field. We use the principle of adiabatic quantum pumping process for entanglement transfer in the spin chain systems. We achieve the perfect entanglement transfer over an arbitrarily long distance and a better entanglement transport for longer AFM spin chain system than for the ferromagnetic one. We explain analytically and physically—why the entanglement hops in alternate sites. We find the condition for blocking of entanglement transport even in the perfect pumping situation. Our analytical solution interconnects quantum many body physics and quantum information science.

Induced modification of the geometric phase of a qubit coupled to an XY spin chain by Dzyaloshinsky-Moriya interaction

We consider a qubit symmetrically and transversely coupled to an XY spin chain with Dzyaloshinsky-Moriya（DM） interaction in the presence of a transverse magnetic field.An analytical expression for the geometric phase of the qubit is obtained in the weak coupling limit.We find that the modification of the geometrical phase induced by the spin chain environment is greatly enhanced by DM interaction in the weak coupling limit around the quantum phase transition point of the spin chain.

Optimal quantum parameter estimation of two-qutrit Heisenberg XY chain under decoherence

Adopting the Milburn decoherence model, we investigate the performance of quantum Fisher information of the twoqutrit isotropic Heisenberg XY chain under decoherence. We find that the quantum Fisher information with respect to the decoherence rate and the magnetic field decreases exponentially in the long-time limit, which significantly reduces the precision of optimal quantum estimation. We also show that with the increase of the decoherence rate or the magnetic field,the QFIs go down considerably. Furthermore, we find that the precision of optimal quantum estimation can be enhanced by the entanglement in the input state.

Doping effect on the structure and physical properties of quasi-one-dimensional compounds Ba_(9)Co_(3)(Se_(1−x)S_(x))_(15)(x=0-0.2)

A series of samples of Ba_(9)Co_(3)(Se_(1−x)S_(x))_(15)(x=0,0.05,0.1,0.15,0.2)with quasi-one-dimensional(1D)structure were successfully synthesized under high-temperature and high-pressure conditions.The influence of partial substitution of S for Se on the structure,electronic transport,and magnetic properties of Ba_(9)Co_(3)(Se_(1−x)S_(x))_(15) has been investigated in detail.The x-ray diffraction data shows that the lattice constant decreases linearly with increasing S-doping level,which follows the Vegrad’s law.The doped S atoms preferentially occupy the site of Se atoms in CoSe6 octahedron.Physical properties measurements indicate that all the samples of Ba_(9)Co_(3)(Se_(1−x)S_(x))_(15) are semiconducting and display spin glass behavior.As the replacement of Se by smaller size S,although the inter-chain distance decreases,the electronic hopping between CoSe/S6 chains is weakened and leads to an increase of band gap from 0.75 eV to 0.86 eV,since the S-3p electrons are more localized than Se-4p ones.Ba_(9)Co_(3)(Se_(1−x)S_(x))_(15) exhibits 1D conducting chain characteristic.

Low-temperature heat transport of the zigzag spin-chain compound SrEr_(2)O_(4)

Low-temperature thermal conductivity(κ),as well as the magnetic properties and specific heat,are studied for the frustrated zigzag spin-chain material Sr Er_(2)O_(4)by using single-crystal samples.The specific heat data indicate the longrange antiferromagnetic transition at~0.73 K and the existence of strong magnetic fluctuations.The magnetizations at very low temperatures for magnetic field along the c axis(spin chain direction)or the a axis reveal the field-induced magnetic transitions.Theκshows a strong dependence on magnetic field,applied along the c axis or the a axis,which is closely related to the magnetic transitions.Furthermore,high magnetic field induces a strong increase ofκ.These results indicate that thermal conductivity along either the c axis or the a axis are mainly contributed by phonons,while magnetic excitations play a role of scattering phonons.