Entanglement and dynamical phase transition in a spin-orbit-coupled Bose-Einstein condensate

Characterizing quantum phase transitions through quantum correlations has been deeply developed for a long time, while the connections between dynamical phase transitions (DPTs) and quantum entanglement is not yet well understood. In this work, we show that the time-averaged two-mode entanglement in the spin space reaches a maximal value when it undergoes a DPT induced by external perturbation in a spin-orbit-coupled Bose-Einstein condensate. We employ the von Neumann entropy and a correlation-based entanglement criterion as entanglement measures and find that both of them can infer the existence of DPT. While the von Neumann entropy works only for a pure state at zero temperature and requires state tomography to reconstruct, the experimentally more feasible correlation-based entanglement criterion acts as an excellent proxy for entropic entanglement and can determine the existence of entanglement for a mixed state at finite temperature, making itself an excellent indicator for DPT. Our work provides a deeper understanding about the connection between DPTs and quantum entanglement, and may allow the detection of DPT via entanglement become accessible as the examined criterion is suitable for measuring entanglement.Comment: 9 pages, 6 figure

Origin of the pseudogap and its influence on superconducting state

When holes move in the background of strong antiferromagnetic correlation, two effects with different spatial scale emerge, leading to a much reduced hopping integral with an additional phase factor. An effective Hamiltonian is then proposed to investigate the underdoped cuprates. We argue that the pseudogap is the consequence of dressed hole moving in the antiferromagnetic background and has nothing to do with the superconductivity. The momentum distributions of the gap are qualitatively consistent with the recent ARPES measurements both in the pseudogap and superconducting state. Two thermal qualities are further calculated to justify our model. A two-gap scenario is concluded to describe the relation between the two gaps.Comment: 7 pages, 5 figure

Spin filtering implemented through Rashba and weak magnetic modulations

We present two theoretical schemes for spin filters in one-dimensional semiconductor quantum wires with spatially modulated Rashba spin-orbit coupling (SOC) as well as weak magnetic potential. For case I, the SOC is periodic and the weak magnetic potential is applied uniformly along the wire. Full spin polarizations with opposite signs are obtained within two separated energy intervals. For case II, the weak magnetic potential is periodic while the SOC is uniform. An ideal negative/positive switching effect for spin polarization is realized by tuning the strength of SOC. The roles of SOC, magnetic potential, and their coupling on the spin filtering are analyzed.Comment: 4 pages, 4 figure

Extended Holographic dark energy

The idea of relating the infrared and ultraviolet cutoffs is applied to Brans-Dicke theory of gravitation. We find that extended holographic dark energy from the Hubble scale or the particle horizon as the infrared cutoff will not give accelerating expansion. The dynamical cosmological constant with the event horizon as the infrared cutoff is a viable dark energy model.Comment: one reference is corrected, 3 pages, no figure,V3: minor correction

Efficient Scheme for Perfect Collective Einstein-Podolsky-Rosen Steering

A practical scheme for the demonstration of perfect one-sided device-independent quantum secret sharing is proposed. The scheme involves a three-mode optomechanical system in which a pair of independent cavity modes is driven by short laser pulses and interact with a movable mirror. We demonstrate that by tuning the laser frequency to the blue (anti-Stokes) sideband of the average frequency of the cavity modes, the modes become mutually coherent and then may collectively steer the mirror mode to a perfect Einstein-Podolsky-Rosen state. The scheme is shown to be experimentally feasible, it is robust against the frequency difference between the modes, mechanical thermal noise and damping, and coupling strengths of the cavity modes to the mirror.Comment: 9 pages, 4 figure

Ideal switching effect in periodic spin-orbit coupling structures

An ideal switching effect is discovered in a semiconductor nanowire with a spatially-periodic Rashba structure. Bistable `ON' and `OFF' states can be realized by tuning the gate voltage applied on the Rashba regions. The energy range and position of `OFF' states can be manipulated effectively by varying the strength of the spin-orbit coupling (SOC) and the unit length of the periodic structure, respectively. The switching effect of the nanowire is found to be tolerant of small random fluctuations of SOC strength in the periodic structure. This ideal switching effect might be applicable in future spintronic devices.Comment: 4 pages and 4 figure