Number Of Spin Flips Research Articles

Dynamic magnetization in non-Hermitian quantum spin systems

We report a global effect induced by the local complex field, associated with the spin-exchange interaction. High-order exceptional point up to ($N+1$)-level coalescence is created at the critical local complex field applied to the $N$-size quantum spin chain. The ($N+1$)-order coalescent level is a saturated ferromagnetic ground state in the isotropic spin system. Remarkably, the final state always approaches the ground state for an arbitrary initial state with any number of spin flips; even if the initial state is orthogonal to the ground state. Furthermore, the switch of macroscopic magnetization is solely driven by the time and forms a hysteresis loop in the time domain. The retentivity and coercivity of the hysteresis loop mainly rely on the non-Hermiticity. Our findings highlight the cooperation of non-Hermiticity and the interaction in quantum spin system, suggest a dynamical framework to realize magnetization, and thus pave the way for the non-Hermitian quantum spin system.

Quantum Entanglement Channel based on Excited States in a Spin Chain

We study the possibility of using a spin chain to construct a quantum entanglement channel that can be used for quantum state transmission in a solid state system. We analyze the spin chain's states under various z-directional magnetic field and spin interactions to determine the entanglement between Alice and Bob's spins. We derive the conditions under which this entanglement can be distilled, and find that a spin chain of arbitrary length can be used as a quantum channel for quantum state transmission when the number of spin flips in the chain is large.

Behavior of the two-dimensional Ising model at the boundary of a half-infinite cylinder

The critical two-dimensional Ising model is studied at the boundary of a half-infinite cylinder for the three regular lattices (square, triangular, and hexagonal). The probability of having precisely 2n spinflips at the boundary is computed as a function of the positions, ki, i = 1, 2, 3, …, 2n, of the spinflips. The limit when the mesh goes to zero is obtained. For the square lattice, the probability of having 2n spinflips, independent of their position, is computed at the critical temperature. As a byproduct, we recover De Coninck’s result showing that the limiting distribution of the number of spinflips is Gaussian and we give explicit expressions for its mean and variance. The results are obtained as consequences of Onsager’s solution and are rigorous.

Universal conductance fluctuations in spin glasses.

Results of numerical studies of conductance of a two-dimensional tight-binding system with random potentials and coupled to a three-dimensional Ising spin glass are presented. Numerical values of the conductance dispersion, in an ensemble of the potentials, support results of diagrammatic calculations for universality classes relevant for this system. Conductance of a sample is studied as a function of ``time'' for various Monte Carlo trajectories of the spin glass. The dispersion of the conductance noise decreases on cooling of the spin system without a noticeable anomaly at ${\mathit{T}}_{\mathit{c}}$. Power spectra of the noise are power laws in frequency with the exponent of -0.5 (at least in the vicinity of ${\mathit{T}}_{\mathit{c}}$) and the amplitude of a spectrum decreases monotonically with T. The fluctuations in the noise are only statistically related to the number of spin flips involved. The dispersion of the fluctuations at a given temperature depends on initial spin configurations. Locations of spins that affect conductance must also depend on the spin configuration. History-dependent effects are present both above and below ${\mathit{T}}_{\mathit{c}}$. Conductance noise in ferromagnets is compared to that occurring in spin glasses.

Internal structure of hole quasiparticles in antiferromagnets.

Holes in an Ising antiferromagnet give rise to quasiparticles with an internal structure associated with the distortion of the spin ordering. We show that the spectrum of excited states (of this internal structure) commences at a lower energy than previously thought, at an energy of the order of the exchange constant. The character of the corresponding states differ from those previously discussed in that the phases associated with the various spin configurations with the same number of spin flips differ. Moreover, these excited states dominate the optical absorption and may explain the experimental results of Thomas et al. [Phys. Rev. Lett. 61, 1313 (1988)].