Spontaneous Symmetry Breaking, Off-diagonal Long-range Order, and Nucleation of Quantum State

Spontaneous nucleation of structural defects in inhomogeneous ion chains

Structural defects in ion crystals can be formed during a linear quench of the transverse trapping frequency across the mechanical instability from a linear chain to the zigzag structure. The density of defects after the sweep can be conveniently described by the Kibble-Zurek mechanism. In particular, the number of kinks in the zigzag ordering can be derived from a time-dependent Ginzburg-Landau equation for the order parameter, here the zigzag transverse size, under the assumption that the ions are continuously laser cooled. In a linear Paul trap the transition becomes inhomogeneous, being th…

Beyond spontaneously broken symmetry in Bose-Einstein condensates

Spontaneous symmetry breaking (SSB) for Bose-Einstein condensates cannot treat phase off-diagonal effects, and thus not explain Bell inequality violations. We describe another situation that is beyond a SSB treatment: an experiment where particles from two (possibly macroscopic) condensate sources are used for conjugate measurements of the relative phase and populations. Off-diagonal phase effects are characterized by a "quantum angle" and observed via "population oscillations", signaling quantum interference of macroscopically distinct states (QIMDS).

Quantum Disentanglement in Long-range Orders and Spontaneous Symmetry Breaking

We investigate the nature of quantum entanglement in long-range orders and spontaneous symmetry breaking. It is shown that diminishing of entanglement between the condensate mode and the rest of the system underlies off-diagonal long-range order, which is the hallmark of superconductivity and Bose-Einstein condensation. It is also revealed that disentanglement underlies various cases of long-range order and spontaneous symmetry breaking. In the course of the discussion, we also present some ideas on characterizing entanglement in many-body systems. Especially, it is shown how the connected cor…

Magnetic Blockade Mechanism for Quantum Nucleation of Superconducting Vortex-Antivortex Pairs in Zero External Magnetic Field

We propose a magnetic dual of the Coulomb blockade effect for quantum nucleation of flux vortex pairs in high-Tc superconducting (HTS) films and grain boundaries in zero applied field. The magnetic blockade instability occurs at θ = π, where θ is the "vacuum" or theta angle. The θ term has recently been discussed in the context of several other systems, including charge and spin density waves, topological insulators, the quantum Hall effect, and spontaneous CP violation. Our model predicts a sharp pair creation threshold current at θ = π, analogous to the Coulomb blockade voltage of a tunnel j…

One-dimensional frustrated plaquette compass model: Nematic phase and spontaneous multimerization

We introduce a one-dimensional (1D) pseudospin model on a ladder where the Ising interactions along the legs and along the rungs alternate between $X_{i}X_{i+1}$ and $Z_{i}Z_{i+1}$ for even/odd bond (rung). We include also the next nearest neighbor Ising interactions on plaquettes' diagonals that alternate in such a way that a model where only leg interactions are switched on is equivalent to the one when only the diagonal ones are present. Thus in the absence of rung interactions the model can interpolate between two 1D compass models. The model posses local symmetries which are the parities …

量子电子波包自发辐射光子发射的形状依赖性及聚束电子束超辐射的QED起源

Shape-Dependence of Spontaneous Photon Emission by Quantum Electron Wavepackets and the QED Origin of Bunched Electron Beam Superradiance

本文揭示了自由电子自发辐射光子态的非经典性依赖于量子电子波函数形状，并通过QED分析证明密度调制电子束中非对角项相位是超辐射（辐射正比于N_e^2）的起源，为增强量子电子相互作用提供了新途径。