Adiabatic State Conversion and Pulse Transmission in Optomechanical Systems

Optomechanical systems with strong coupling can be a powerful medium for quantum state engineering. Here, we show that quantum state conversion between cavity modes with different wavelengths can be realized with high fidelity by adiabatically varying the effective optomechanical couplings. The fidelity for the conversion of gaussian states is derived by solving the Langevin equation in the adiabatic limit. We also show that photon pulses can be transmitted between input-output channels with different wavelengths via the effective optomechanical couplings and the output pulse shape can also be manipulated.Comment: 5 pages, 2 figures. Supplementary Materials at http://prl.aps.org/supplemental/PRL/v108/i15/e15360

Universal Quantum Degeneracy Point for Superconducting Qubits

The quantum degeneracy point approach [D. Vion et al., Science 296, 886 (2002)] effectively protects superconducting qubits from low-frequency noise that couples with the qubits as transverse noise. However, low-frequency noise in superconducting qubits can originate from various mechanisms and can couple with the qubits either as transverse or as longitudinal noise. Here, we present a quantum circuit containing a universal quantum degeneracy point that protects an encoded qubit from arbitrary low-frequency noise. We further show that universal quantum logic gates can be performed on the encoded qubit with high gate fidelity. The proposed scheme is robust against small parameter spreads due to fabrication errors in the superconducting qubits.Comment: 7 pages, 4 figure

Thermal analysis of Phase Change Material Board (PCMB) under weather conditions in the summer

This document is the Accepted Manuscript version of the following article: D. Zhuo, Y. tian, Y. Qu, and Y. K. Chen, ‘Thermal analysis of phase change material board (PCMB) under weather conditions in the summer’, Applied Thermal Engineering, Vol. 99: 690-702, April 2016, doi: https://doi.org/10.1016/j.applthermaleng.2016.01.121. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/.Phase Change Material Board (PCMB) has been considered as an effective way to improve the thermal comfort in either new or existing buildings. In this work, firstly the optimal melting temperatures of internal and external PCMB are given, and the optimal heat storage capacities are obtained under the idealised circumstance of considering sinusoidal changes of the room and outdoor temperatures during a day. Secondly, to study the potential energy saving from applying a PCMB, a case study of a lightweight office with real environmental conditions is carried out. The air conditioning is switched on in the model to keep the indoor temperature within thermal comfort. Using the daily energy consumption and daily thermal comfort rate as the performance criteria, the effects of major influencing factors including melting temperature, latent heat and thermal conductivity of PCMB are studied parametrically. The results show that both the external and internal PCMB can achieve better performance when the melting temperature is chosen to be slightly higher than the average indoor air temperature. In the summer, the external PCMB has a better performance than the internal PCMB because the external PCMB works not only as a heat storage system whose function is similar to the internal PCMB, but also as a thermal connection between the outdoor and indoor environment due to its thermal insulation function, which reduces the influence of the changing outdoor environment.Peer reviewedFinal Accepted Versio

Thermal stress-induced charge and structure heterogeneity in emerging cathode materials

Nickel-rich layered oxide cathode materials are attractive near-term candidates for boosting the energy density of next generation lithium-ion batteries. The practical implementation of these materials is, however, hindered by unsatisfactory capacity retention, poor thermal stability, and oxygen release as a consequence of structural decomposition, which may have serious safety consequences. The undesired side reactions are often exothermic, causing complicated electro-chemo-mechanical interplay at elevated temperatures. In this work, we explore the effects of thermal exposure on chemically delithiated LiNi0.8Mn0.1Co0.1O2 (NMC-811) at a practical state-of-charge (50% Li content) and an over-charged state (25% Li content). A systematic study using a suite of advanced synchrotron radiation characterization tools reveals the dynamics of thermal behavior of the charged NMC-811, which involves sophisticated structural and chemical evolution; e.g. lattice phase transformation, transition metal (TM) cation migration and valence change, and lithium redistribution. These intertwined processes exhibit a complex 3D spatial heterogeneity and, collectively, form a valence state gradient throughout the particles. Our study sheds light on the response of NMC-811 to elevated temperature and highlights the importance of the cathode's thermal robustness for battery performance and safety

The perfect spin injection in silicene FS/NS junction

We theoretically investigate the spin injection from a ferromagnetic silicene to a normal silicene (FS/NS), where the magnetization in the FS is assumed from the magnetic proximity effect. Based on a silicene lattice model, we demonstrated that the pure spin injection could be obtained by tuning the Fermi energy of two spin species, where one is in the spin orbit coupling gap and the other one is outside the gap. Moreover, the valley polarity of the spin species can be controlled by a perpendicular electric field in the FS region. Our findings may shed light on making silicene-based spin and valley devices in the spintronics and valleytronics field.Comment: 6 pages, 3 figure

Integer quantum Hall effect and topological phase transitions in silicene

We numerically investigate the effects of disorder on the quantum Hall effect (QHE) and the quantum phase transitions in silicene based on a lattice model. It is shown that for a clean sample, silicene exhibits an unconventional QHE near the band center, with plateaus developing at $\nu=0,\pm2,\pm6,\ldots,$ and a conventional QHE near the band edges. In the presence of disorder, the Hall plateaus can be destroyed through the float-up of extended levels toward the band center, in which higher plateaus disappear first. However, the center $\nu=0$ Hall plateau is more sensitive to disorder and disappears at a relatively weak disorder strength. Moreover, the combination of an electric field and the intrinsic spin-orbit interaction (SOI) can lead to quantum phase transitions from a topological insulator to a band insulator at the charge neutrality point (CNP), accompanied by additional quantum Hall conductivity plateaus.Comment: 7 pages, 4 figure

Calabi-Yau manifolds from pairs of non-compact Calabi-Yau manifolds

Most of Calabi-Yau manifolds that have been considered by physicists are complete intersection Calabi-Yau manifolds of toric varieties or some quotients of product types. Purpose of this paper is to introduce a different and rather new kind of construction method of Calabi-Yau manifolds by pasting two non-compact Calabi-Yau manifolds. We will also in some details explain a curious and mysterious similarity with construction of some $G_2$-manifolds (also called Joyce manifolds), which are base spaces for M-theory.Comment: 10 pages. Accepted for publication in JHE

Radiance and Doppler shift distributions across the network of the quiet Sun

The radiance and Doppler-shift distributions across the solar network provide observational constraints of two-dimensional modeling of transition-region emission and flows in coronal funnels. Two different methods, dispersion plots and average-profile studies, were applied to investigate these distributions. In the dispersion plots, we divided the entire scanned region into a bright and a dark part according to an image of Fe xii; we plotted intensities and Doppler shifts in each bin as determined according to a filtered intensity of Si ii. We also studied the difference in height variations of the magnetic field as extrapolated from the MDI magnetogram, in and outside network. For the average-profile study, we selected 74 individual cases and derived the average profiles of intensities and Doppler shifts across the network. The dispersion plots reveal that the intensities of Si ii and C iv increase from network boundary to network center in both parts. However, the intensity of Ne viii shows different trends, namely increasing in the bright part and decreasing in the dark part. In both parts, the Doppler shift of C iv increases steadily from internetwork to network center. The average-profile study reveals that the intensities of the three lines all decline from the network center to internetwork region. The binned intensities of Si ii and Ne viii have a good correlation. We also find that the large blue shift of Ne viii does not coincide with large red shift of C iv. Our results suggest that the network structure is still prominent at the layer where Ne viii is formed in the quiet Sun, and that the magnetic structures expand more strongly in the dark part than in the bright part of this quiet Sun region.Comment: 10 pages,9 figure