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Dynamic fragmentation in a quenched two-mode Bose–Einstein condensate
Shu-Yuan Wu (吴淑媛),Hong-Hua Zhong (钟宏华),Jia-Hao Huang (黄嘉豪),Xi-Zhou Qin (秦锡洲),Chao-Hong Lee (李朝红)
Front. Phys. . 2016, 11 (3 ): 101204-.
https://doi.org/10.1007/s11467-015-0530-9
We investigate the fragmentation in a two-mode Bose–Einstein condensate with Josephson coupling. We explore how the fragmentation and entropy of the ground state depend on the intermode asymmetry and interparticle interactions. Owing to the interplay between the asymmetry and the interactions, a sequence of notches and plateaus in the fragmentation appears with the single-atom tunneling and interaction blockade, respectively. We then analyze the dynamical properties of the fragmentation in three typical quenches of the asymmetry: linear, sudden, and periodic quenches. In a linear quench, the final state is a fragmented state due to the sequential Landau–Zener tunneling, which can be analytically explained by applying the two-level Landau–Zener formula for each avoided level crossing. In a sudden quench, the fragmentation exhibits persistent fluctuations that sensitively depend on the interparticle interactions and intermode coupling. In a periodic quench, the fragmentation is modulated by the periodic driving, and a suitable modulation may allow one to control the fragmentation.
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3D entangled fractional squeezing transformation and its quantum mechanical correspondence
Fang Jia,Shuang Xu,Cheng-Zhi Deng,Cun-Jin Liu,Li-Yun Hu
Front. Phys. . 2016, 11 (3 ): 110302-.
https://doi.org/10.1007/s11467-015-0538-1
A new type of entangled fractional squeezing transformation (EFrST) has been theoretically proposed for 2D entanglement [Front. Phys. 10, 100302 (2015)]. In this paper, we shall extend this case to that of 3D entanglement by introducing a type of three-mode entangled state representation, which is not the product of three 1D cases. Using the technique of integration within an ordered product of operators, we derive a compact unitary operator corresponding to the 3D fractional entangling transformation, which is an entangling operator that presents a clear transformation relation. We also verified that the additivity property of the novel 3D EFrST is of a Fourier character by using its quantum mechanical description. As an application of this representation, the EFrST of the three-mode number state is calculated using the quantum description of the EFrST.
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Quantum superreplication of states and gates
Giulio Chiribella,Yuxiang Yang
Front. Phys. . 2016, 11 (3 ): 110304-.
https://doi.org/10.1007/s11467-016-0556-7
Although the no-cloning theorem forbids perfect replication of quantum information, it is sometimes possible to produce large numbers of replicas with vanishingly small error. This phenomenon, known as quantum superreplication, can occur for both quantum states and quantum gates. The aim of this paper is to review the central features of quantum superreplication and provide a unified view of existing results. The paper also includes new results. In particular, we show that when quantum superreplication can be achieved, it can be achieved through estimation up to an error of size O (M /N 2 ), where N and M are the number of input and output copies, respectively. Quantum strategies still offer an advantage for superreplication in that they allow for exponentially faster reduction of the error. Using the relation with estimation, we provide i) an alternative proof of the optimality of Heisenberg scaling in quantum metrology, ii) a strategy for estimating arbitrary unitary gates with a mean square error scaling as log N /N 2 , and iii) a protocol that generates O (N 2 ) nearly perfect copies of a generic pure state U |0>while using the corresponding gate U only N times. Finally, we point out that superreplication can be achieved using interactions among k systems, provided that k is large compared to M 2 /N 2 .
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Using X (3823)→J /ψ π+ π− to identify coupled-channel effects
Bo Wang,Hao Xu,Xiang Liu,Dian-Yong Chen,Susana Coito,Estia Eichten
Front. Phys. . 2016, 11 (3 ): 111402-.
https://doi.org/10.1007/s11467-016-0564-7
Very recently, the Belle and BESIII experiments observed a new charmonium-like state X (3823), which is a good candidate for the D -wave charmonium ψ (13 D 2 ). Because the X (3823) is just near the D ¯D ∗ threshold, the decay X (3823)→ J /ψ π+ π− can be a golden channel to test the significance of coupled-channel effects. In this work, this decay is considered including both the hidden-charm dipion and the usual quantum chromodynamics multipole expansion (QCDME) contributions. The partial decay width, the dipion invariant mass spectrum distribution dΓ [X (3823) → J /ψ π+ π− ]/dmπ + π − , and the corresponding dΓ [X (3823) → J /ψ π+ π− ]/d cos θ distribution are computed. Many parameters are determined from existing experimental data, so the results depend mainly only on one unknown phase between the QCDME and hidden-charm dipion amplitudes.
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Enhanced phase sensitivity of an SU(1,1) interferometer with displaced squeezed vacuum light
Xiao-Yu Hu (胡小玉),Chao-Ping Wei (魏朝平),Ya-Fei Yu (於亚飞),Zhi-Ming Zhang(张智明)
Front. Phys. . 2016, 11 (3 ): 114203-.
https://doi.org/10.1007/s11467-015-0547-0
We study the phase sensitivity of an SU(1,1) interferometer with two input beams in the displaced squeezed vacuum state and the coherent state, respectively. We find that there exists an optimal squeezing fraction of the displaced squeezed vacuum state that optimizes the phase sensitivity. We also examine the effects of some factors, including the loss, mean photon number of the input beams and amplitude gain of the optical parameter amplifiers, on the optimal squeezing fraction so that we can choose the optimal values to enhance the phase sensitivity.
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Thermoelectric response of spin polarization in Rashba spintronic systems
Cong Xiao,Dingping Li,Zhongshui Ma
Front. Phys. . 2016, 11 (3 ): 117201-.
https://doi.org/10.1007/s11467-016-0566-5
Motivated by the recent discovery of a strongly spin–orbit-coupled two-dimensional (2D) electron gas near the surface of Rashba semiconductors BiTeX (X= Cl, Br, I), we calculate the thermoelectric responses of spin polarization in a 2D Rashba model. By self-consistently determining the energyand band-dependent transport time, we present an exact solution of the linearized Boltzmann equation for elastic scattering. Using this solution, we find a non-Edelstein electric-field-induced spin polarization that is linear in the Fermi energy E F when E F lies below the band crossing point. The spin polarization efficiency, which is the electric-field-induced spin polarization divided by the driven electric current, increases for smaller E F .We show that, as a function of E F , the temperaturegradient-induced spin polarization increases continuously to a saturation value when EF decreases below the band crossing point. As the temperature tends to zero, the temperature-gradient-induced spin polarization vanishes.
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Two-body physics in quasi-low-dimensional atomic gases under spin–orbit coupling
Jing-Kun Wang,Wei Yi,Wei Zhang
Front. Phys. . 2016, 11 (3 ): 118102-.
https://doi.org/10.1007/s11467-015-0529-2
One of the most dynamic directions in ultracold atomic gas research is the study of low-dimensional physics in quasi-low-dimensional geometries, where atoms are confined in strongly anisotropic traps. Recently, interest has significantly intensified with the realization of synthetic spin–orbit coupling (SOC). As a first step toward understanding the SOC effect in quasi-low-dimensional systems, the solution of two-body problems in different trapping geometries and different types of SOC has attracted great attention in the past few years. In this review, we discuss both the scattering-state and the bound-state solutions of two-body problems in quasi-one and quasi-two dimensions. We show that the degrees of freedom in tightly confined dimensions, in particular with the presence of SOC, may significantly affect system properties. Specifically, in a quasi-one-dimensional atomic gas, a one-dimensional SOC can shift the positions of confinement-induced resonances whereas, in quasitwo-dimensional gases, a Rashba-type SOC tends to increase the two-body binding energy, such that more excited states in the tightly confined direction are occupied and the system is driven further away from a purely two-dimensional gas. The effects of the excited states can be incorporated by adopting an effective low-dimensional Hamiltonian having the form of a two-channel model. With the bare parameters fixed by two-body solutions, this effective Hamiltonian leads to qualitatively different many-body properties compared to a purely low-dimensional model.
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Properties of spin–orbit-coupled Bose–Einstein condensates
Yongping Zhang,Maren Elizabeth Mossman,Thomas Busch,Peter Engels,Chuanwei Zhang
Front. Phys. . 2016, 11 (3 ): 118103-.
https://doi.org/10.1007/s11467-016-0560-y
The experimental and theoretical research of spin–orbit-coupled ultracold atomic gases has advanced and expanded rapidly in recent years. Here, we review some of the progress that either was pioneered by our own work, has helped to lay the foundation, or has developed new and relevant techniques. After examining the experimental accessibility of all relevant spin–orbit coupling parameters, we discuss the fundamental properties and general applications of spin–orbit-coupled Bose–Einstein condensates (BECs) over a wide range of physical situations. For the harmonically trapped case, we show that the ground state phase transition is a Dicke-type process and that spin–orbit-coupled BECs provide a unique platform to simulate and study the Dicke model and Dicke phase transitions. For a homogeneous BEC, we discuss the collective excitations, which have been observed experimentally using Bragg spectroscopy. They feature a roton-like minimum, the softening of which provides a potential mechanism to understand the ground state phase transition. On the other hand, if the collective dynamics are excited by a sudden quenching of the spin–orbit coupling parameters, we show that the resulting collective dynamics can be related to the famous Zitterbewegung in the relativistic realm. Finally, we discuss the case of a BEC loaded into a periodic optical potential. Here, the spin–orbit coupling generates isolated flat bands within the lowest Bloch bands whereas the nonlinearity of the system leads to dynamical instabilities of these Bloch waves. The experimental verification of this instability illustrates the lack of Galilean invariance in the system.
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Optical properties of Au-core Pt-shell nanorods studied using FDTD simulations
Jian-Bo Liu,Lin Long,Yu-Shi Zhang,Yue-Ping Wang,Feng-Shou Liu,Wei-Yao Xu,Ming-Ji Zong,Lei Ma,Wen-Qi Liu,Hui Zhang,Jiao Yan,Jia-Qi Chen,Ying-Lu Ji,Xiao-Chun Wu
Front. Phys. . 2016, 11 (3 ): 118501-.
https://doi.org/10.1007/s11467-015-0528-3
Au-core/Pt-shell nanorods (Au@Pt NRs) have been prepared by a Au nanorod-mediated growth method, and they exhibit high electromagnetic field enhancements under coupling conditions. Boosted by a long-range effect of the high electromagnetic field generated by the Au core, the electromagnetic field enhancement can be controlled by changing the morphology of the nanostructures. In this study, we report the results on the simulations of the electromagnetic field enhancement using a finite difference time domain (FDTD) method, taking the real shapes of the Au@Pt NRs into account. Due to the “hot spot” effect, the electromagnetic field can be localized between the Pt nanodots. The electromagnetic field enhancement is found to be rather independent of the Pt content, whereas the local roughness and small sharp features might significantly modify the near-field. As the electromagnetic field enhancement can be tuned by the distribution of Pt nanodots over the Au-core, Au@Pt NRs can find potential applications in related areas.
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15 articles