In this paper, we investigate coherence protection of a quantum system coupled to a hierarchical environment by utilizing noise. As an example, we solve the Jaynes-Cummings model in the presence of both a classical and a quantized noise. The master equation is derived beyond the Markov approximation, where the influence of memory effects from both noises is taken into account. More importantly, we find that the performance of the coherence protection sensitively depends on the non-Markovian properties of both noises. By analyzing the mathematical mechanism of the coherence protection, we show the decoherence caused by a non-Markovian noise with longer memory time can be suppressed by another Markovian noise with shorter memory time. Last but not least, as an outlook, we try to analyze the connection between the atom-cavity entanglement and the atomic coherence, then discuss the possible clue to search the required noise. The results presented in this paper show the possibility of protecting coherence by utilizing noise and may open an alternative path to design noise-assisted coherence protection schemes.

The Na_xWO₃ nanoparticles with different x were synthesized by a solvothermal method and the absorption behavior in visible and near-infrared light (NIR) region was studied. Well-crystallized nanoparticles with sizes of several tens of nanometers were confirmed by XRD, SEM and TEM methods. The absorption valley in visible region shifted from 555 nm to 514 nm and the corresponding absorption peak in NIR region shifted from 1733 nm to 1498 nm with the increasing x. In addition, the extinction behavior of Na_xWO₃ nanoparticles with higher x values were simulated by discrete dipole approximation method and results showed that the changing behavior of optical properties was in good agreement with the experimental results. The experimental and theoretical data indicate that the transparency and NIR-shielding properties of Na_xWO₃ nanoparticles in the visible and NIR region can be continuously adjusted by x value in the whole range of 0 < x < 1. These tunable optical properties of nanocrystalline Na_xWO₃ will expand its application in the fields of transparent heat-shielding materials or optical filters.

We investigate spin squeezing for a one-axis twisting (OAT) model coupled to a general non-Markovian environment in a finite-temperature regime. Using the non-Markovian quantum state diffusion and master equation approach, we numerically study non-Markovian spin-squeezing generation in the OAT model. Our results show that the total spin number $N$, energy $k_{B}T$, and certain coefficients in the OAT model can play a crucial role in generating spin squeezing. In particular, it shows that the maximum spin squeezing can be significantly enhanced when the participating environment has a relatively long memory time.

The piezoelectric optomechanical devices supply a promising experimental platform to realize the coherent and effective control and measurement of optical circuits working in Terahertz (THz) frequencies via superconducting electron devices typically working in Radio (MHz) frequencies. However, quantum fluctuations are unavoidable when the size of mechanical oscillators enter into the nanoscale. The consequences of the noisy environment are still challenging due to the lack of analytical tools. In this paper, a semi-classical and full-quantum model of piezoelectric optomechanical systems coupled to a noisy bosonic quantum environment are introduced and solved in terms of quantum-state diffusion (QSD) trajectories in the non-Markovian regime. We show that the noisy environment, particularly the central frequency of the environment, can enhance the entanglement generation between optical cavities and LC circuits in some parameter regimes. Moreover, we observe the critical points in the coefficient functions, which can lead the different behaviors in the system. Besides, we also witness the entanglement transfers between macroscopic objects due to the memory effect of the environment. Our work can be applied in the fields of electric/ optical switches, and long-distance distribution in a large-scale quantum network.

The dynamics of chaos in quantum systems has attracted much interest in connection with the fundamental aspects of quantum mechanics. We study the chaotic dynamics of both the excitonic mode and the cavity mode in a microcavity containing a quantum well driven by an external field. We investigate how the chaotic dynamics is influenced by the frequencies of the exciton and the cavity, the coupling constant between the exciton and cavity, the Coulomb interaction between excitons, and the response of the exciton to the cavity and the external field. We show that chaos can be generated synchronously in both the cavity and the excitonic mode by choosing appropriate parameters. Moreover, this kind of chaos can be controlled by the coupling constant, the strength of the interaction between excitons, the external field, the response of the excitons to the cavity, and the detuning between the cavity field and the excitonic field. The present study may have applications in chaos-based neural networks and extreme event statistics.

As one kind of many body entangled states, spin squeezed states can be used to implement the high precise measurement beyond the standard quantum limit. Inspired by the novel spin squeezing scheme based on phonon-induced spin-spin interactions [S. D. Bennett et al., Phys. Rev. Lett. 110, 156402 (2013)], we reexamine the steady-state behaviors for the spin ensemble in diamond nanostructures by exerting a controllable microwave field. By using the phase-space approach we calculate analytically fluctuations of collective spin operators. We find that there is bistability and spin squeezing for the steady-state spin ensemble, despite the mechanical damping considered. Moreover, our work shows that bistability and spin squeezing can be controlled by microwave field and Zeeman splitting. The present scheme can be used to increase the stability of spin clocks, magnetometers, and other measurements based on spin-spin interaction in diamond nanostructures.