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The environment-induced decoherence of a quantum open system makes it fundamentally import to preserve the initial quantum information of the system in its steady state. Here we study information preservation of two maximally entangled qubits lying inside a photonic-crystal waveguide with semi-infinite cavity-array structure. We generalize our study to arbitrary position and arbitrary frequency detuning of the qubits. We find that for weak qubits-waveguide couplings, the information preservation greatly depends on the position and the frequency detuning of the qubits, while for strong couplings, both of these dependence is significantly weakened. Interestingly, by suitably choosing the position and the frequency of the qubits, high information preservation could be achieved for both weak and strong couplings, irrespective to Markovian or non-Markovian dynamics. Physically, we analytically verify that the ability of information preservation is indeed determined by the existence of the bound states of the entire system, but the probability of information preservation is closely related to the probability of the initial state of the qubits in the bound states. Our results provide an alternative route getting high information preservation without any external controls of the system.

We propose a simple scheme to realize the persistent spin-nematic squeezing in a spinor Bose–Einstein condensate by rapidly turning-off the external magnetic field at a time that maximal spin-nematic squeezing occurs. We observe that the optimal spin-nematic squeezing can be maintained in a nearly fixed direction. For a proper initial magnetic field, the optimal squeezing can be obviously enhanced. We further construct a spin-mixing interferometer, where the quantum correlation of the squeezed state (generated by our scheme) is fully utilized in the phase measurement, and show the phase sensitivity of the interferometer has a significant enhancement.

In this paper, we are concerned with one of the generalized short wave equations proposed by Hone et al (2018 Lett. Math. Phys 108 927). We show that the derivative form of this equation can be viewed as a short wave limit of the Novikov (sw-Novikov) equation. Furthermore, this generalized short wave equation and its derivative form are found to be connected to period 3 reduction of two-dimensional CKP(BKP)-Toda hierarchy, same as the short wave limit of the Depasperis–Procesi (sw-DP) equation. We propose a two-component short wave equation which contain the sw-Novikov equation and sw-DP equation as two special cases. As a main result, we construct two types of integrable semi-discretizations via Hirota’s bilinear method and provide multi-soliton solution to the semi-discrete sw-Novikov equation.

The one-dimensional optimal system for the Lie symmetry group of the (2+1)-dimensional Wu—Zhang equation is constructed by the general and systematic approach. Based on the optimal system, the complete and inequivalent symmetry reduction systems are presented in the form of table. It is noteworthy that a new Painleve integrable equation with constant coefficient is in the table besides the classic Boussinesq equation and the steady case of the Wu-Zhang equation.

The PLA/PHBV/PBAT blends with varied ratio were extruded into filaments by a 3D consumables extruder and the dumbbell-shaped specimens were prepared by a desktop 3D printer. The properties of composites and printed samples were characterized by x-ray diffraction (XRD), differential scanning calorimetry (DSC), melt flow index (MFI), scanning electron microscope (SEM) and tensile strength test. The process parameters of 3D printing were also surveyed. Compared with injection molded specimens with identical composition, the PLA crystallinity of printed specimens was greatly improved; SEM micrographs of the 3D printed specimens fracture surface showed a more uniform microstructure distribution with smaller oval cavities structure; and the 3D printed specimens exhibited superior tensile strength and elongation at break. This study may expand the application fields of PLA based 3D printing filaments.

Pairwise correlation is really an important property for multi-qubit states. For the two-qubit X states extracted from Dicke states and their superposition states, we obtain a compact expression of the quantum discord by numerical check. We then apply the expression to discuss the quantum correlation of the reduced two-qubit states of Dicke states and their superpositions, and the results are compared with those obtained by entanglement of formation, which is a quantum entanglement measure., Comment: 17pages, 8 figures,slightly improved and slightly extended version,and added some references

The dark Korteweg-de Vries (KdV) systems are defined and classified by Kupershmidt sixteen years ago. However, there is no other classifications for other kinds of nonlinear systems. In this paper, a complete scalar classification for dark modified KdV (MKdV) systems is obtained by requiring the existence of higher order differential polynomial symmetries. Different to the nine classes of the dark KdV case, there exist twelve independent classes of the dark MKdV equations. Furthermore, for the every class of dark MKdV system, there is a free parameter. Only for a fixed parameter, the dark MKdV can be related to dark KdV via suitable Miura transformation. The recursion operators of two classes of dark MKdV systems are also given.

We study the dynamical properties in a non-Hermitian Bose-Hubbard dimer and show that the steady state consists mostly of the eigenstate whose eigenvalue has the largest imaginary part. A sharp phase transition occurs in the steady state and the phase transition occurs for a finite particle number, not for infinite ones, in contrast to the Hermitian system. We also investigate the quantum Fisher information and entanglement in two different phases. The results show that the steady state in the Josephson oscillation regime is fully N-particle entangled and the corresponding parameter sensitivity approaches the Heisenberg limit. In the self-trapping regime, the parameter sensitivity just scales as the shot-noise limit. Moreover, quantum Fisher information of the steady state is robust to the initial state, which indicates that the non-Hermitian dynamics takes more advantage than the Hermitian one for quantum metrology.

Partial entangling power provides the average amount of entanglement produced by a d1 × d2 bipartite unitary operator. The average is done over the initial distribution of the states of one of the subsystems. In this paper, we extend the expression of the partial entangling power to the case that d1 is finite and d2 is arbitrary. In particular, we give an explicit expression of partial entangling power for the 2 × ∞ system. The expression can be well applicable to the Jaynes–Cummings model (JCM). The results can recover the well-known phenomenon in the JCM. We explicitly discuss its behaviour in the large detuning case and at the resonance case. Comparing the two cases, we find that it is easier for the JCM in the large detuning case to reach and maintain its maximum entangling power, while for the JCM at resonance, the achievable maximum entangling power is larger. In addition, the time average partial entangling power is also discussed.

We make use of the operator fidelity and its susceptibility to study the quantum phase transition (QPT) of the spin-1/2 XX spin chain with three-spin interaction. The analytical results of operator fidelity and the susceptibility are obtained. From the numerical results one can see that the operator fidelity and its susceptibility present nontrivial behaviors at the critical point. We also consider the (1/2, 1) XXZ mixed-spin chain in which the ground states are degenerate. The operator fidelity approach is still effective to indicate the QPT in this system. We also generally analyze the relation between operator fidelity and QPT.

We use reduced fidelity approach to characterize quantum phase transitions in the one-dimensional spin-1/2 dimerized Heisenberg chain in the antiferromagnetic case. The reduced fidelity susceptibilities between two nearest-neighboring spin pairs are considered. We find that they are directly related to the square of the second derivative of the ground-state energy. This enables us to conclude that the former might be a more effective indicator of the second-order quantum phase transitions than the latter. Two further exemplifications are given to confirm the conclusion is available for a broad class of systems with SU(2) and translation symmetries. Moreover, a general connection between reduced fidelity susceptibility and quantum phase transitions is illustrated.