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Multiple teleportation via partially entangled GHZ state
Pei-Ying Xiong,Xu-Tao Yu,Hai-Tao Zhan,Zai-Chen Zhang
Frontiers of Physics. 2016, 11 (4 ): 110303-.
https://doi.org/10.1007/s11467-016-0553-x
Quantum teleportation is important for quantum communication. We propose a protocol that uses a partially entangled Greenberger–Horne–Zeilinger (GHZ) state for single hop teleportation. Quantum teleportation will succeed if the sender makes a Bell state measurement, and the receiver performs the Hadamard gate operation, applies appropriate Pauli operators, introduces an auxiliary particle, and applies the corresponding unitary matrix to recover the transmitted state.We also present a protocol to realize multiple teleportation of partially entangled GHZ state without an auxiliary particle. We show that the success probability of the teleportation is always 0 when the number of teleportations is odd. In order to improve the success probability of a multihop, we introduce the method used in our single hop teleportation, thus proposing a multiple teleportation protocol using auxiliary particles and a unitary matrix. The final success probability is shown to be improved significantly for the method without auxiliary particles for both an odd or even number of teleportations.
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Dissipation equation of motion approach to open quantum systems
YiJing Yan,Jinshuang Jin,Rui-Xue Xu,Xiao Zheng
Frontiers of Physics. 2016, 11 (4 ): 110306-.
https://doi.org/10.1007/s11467-016-0513-5
This paper presents a comprehensive account of the dissipaton-equation-of-motion (DEOM) theory for open quantum systems. This newly developed theory treats not only the quantum dissipative systems of primary interest, but also the hybrid environment dynamics that are also experimentally measurable. Despite the fact that DEOM recovers the celebrated hierarchical-equations-of-motion (HEOM) formalism, these two approaches have some fundamental differences. To show these differences, we also scrutinize the HEOM construction via its root at the influence functional path integral formalism. We conclude that many unique features of DEOM are beyond the reach of the HEOM framework. The new DEOM approach renders a statistical quasi-particle picture to account for the environment, which can be either bosonic or fermionic. The review covers the DEOM construction, the physical meanings of dynamical variables, the underlying theorems and dissipaton algebra, and recent numerical advancements for efficient DEOM evaluations of various problems. We also address the issue of high-order many-dissipaton truncations with respect to the invariance principle of quantum mechanics of Schrödinger versus Heisenberg prescriptions. DEOM serves as a universal tool for characterizing of stationary and dynamic properties of system-and-bath interferences, as highlighted with its real-time evaluation of both linear and nonlinear current noise spectra of nonequilibrium electronic transport.
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Stochastic description of quantum Brownian dynamics
Yun-An Yan,Jiushu Shao
Frontiers of Physics. 2016, 11 (4 ): 110309-110309.
https://doi.org/10.1007/s11467-016-0570-9
Classical Brownian motion has well been investigated since the pioneering work of Einstein, which inspired mathematicians to lay the theoretical foundation of stochastic processes. A stochastic formulation for quantum dynamics of dissipative systems described by the system-plus-bath model has been developed and found many applications in chemical dynamics, spectroscopy, quantum transport, and other fields. This article provides a tutorial review of the stochastic formulation for quantum dissipative dynamics. The key idea is to decouple the interaction between the system and the bath by virtue of the Hubbard-Stratonovich transformation or It? calculus so that the system and the bath are not directly entangled during evolution, rather they are correlated due to the complex white noises introduced. The influence of the bath on the system is thereby defined by an induced stochastic field, which leads to the stochastic Liouville equation for the system. The exact reduced density matrix can be calculated as the stochastic average in the presence of bath-induced fields. In general, the plain implementation of the stochastic formulation is only useful for short-time dynamics, but not efficient for long-time dynamics as the statistical errors go very fast. For linear and other specific systems, the stochastic Liouville equation is a good starting point to derive the master equation. For general systems with decomposable bath-induced processes, the hierarchical approach in the form of a set of deterministic equations of motion is derived based on the stochastic formulation and provides an effective means for simulating the dissipative dynamics. A combination of the stochastic simulation and the hierarchical approach is suggested to solve the zero-temperature dynamics of the spin-boson model. This scheme correctly describes the coherent-incoherent transition (Toulouse limit) at moderate dissipation and predicts a rate dynamics in the overdamped regime. Challenging problems such as the dynamical description of quantum phase transition (localization) and the numerical stability of the trace-conserving, nonlinear stochastic Liouville equation are outlined.
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The role of microwaves in the enhancement of laser-induced plasma emission
Ali Khumaeni,Katsuaki Akaoka,Masabumi Miyabe,Ikuo Wakaida
Frontiers of Physics. 2016, 11 (4 ): 114209-.
https://doi.org/10.1007/s11467-016-0581-6
We studied experimentally the effect of microwaves (MWs) on the enhancement of plasma emission achieved by laser-induced breakdown spectroscopy (LIBS). A laser plasma was generated on a calcium oxide pellet by a Nd:YAG laser (5 mJ, 532 nm, 8 ns) in reduced-pressure argon surrounding gas. A MW radiation (400 W) was injected into the laser plasma via a loop antenna placed immediately above the laser plasma to enhance the plasma emission. The results confirmed that when the electromagnetic field was introduced into the laser plasma region by the MWs, the lifetime of the plasma was extended from 50 to 500 s, similar to the MW duration. Furthermore, the plasma temperature and electron density increased to approximately 10900 K and 1.5×1018 cm−3 , respectively and the size of the plasma emission was extended to 15 mm in diameter. As a result, the emission intensity of Ca lines obtained using LIBS with MWs was enhanced by approximately 200 times compared to the case of LIBS without MWs.
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Impurity scattering effect in Pd-doped superconductor SrPt3 P
Kang-Kang Hu,Bo Gao,Qiu-Cheng Ji,Yong-Hui Ma,Hui Zhang,Gang Mu,Fu-Qiang Huang,Chuan-Bing Cai,Xiao-Ming Xie
Frontiers of Physics. 2016, 11 (4 ): 117403-.
https://doi.org/10.1007/s11467-016-0554-9
We present a systematic study of the impurity scattering effect induced by Pd dopants in the superconductor SrPt3 P. Using a solid-state reaction method, we fabricated the Pd-doped superconductor Sr(Pt1−x Pdx )3 P.We found that the residual resistivity ρ 0 increases quickly with Pd doping, whereas the residual resistance ratio (RRR) displays a dramatic reduction. In addition, both the nonlinear field-dependent behavior of the Hall resistivity ρ xy and the strong temperature dependence of the Hall coefficient R H at low temperature are suppressed by Pd doping. All the experimental results can be explained by an increase in scattering by impurities induced by doping. Our results suggest that the Pt position is very crucial to the carrier conduction in the present system.
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Physical basis for the symmetries in the Friedmann–Robertson–Walker metric
Fulvio Melia
Frontiers of Physics. 2016, 11 (4 ): 119801-.
https://doi.org/10.1007/s11467-016-0557-6
Modern cosmological theory is based on the Friedmann–Robertson–Walker (FRW) metric. Often written in terms of co-moving coordinates, this well-known solution to Einstein’s equations owes its elegant and highly practical formulation to the cosmological principle and Weyl’s postulate, upon which it is founded. However, there is physics behind such symmetries, and not all of it has yet been recognized. In this paper, we derive the FRW metric coefficients from the general form of the spherically symmetric line element and demonstrate that, because the co-moving frame also happens to be in free fall, the symmetries in FRW are valid only for a medium with zero active mass. In other words, the spacetime of a perfect fluid in cosmology may be correctly written as FRW only when its equation of state is ρ +3p = 0, in terms of the total pressure p and total energy density ρ . There is now compelling observational support for this conclusion, including the Alcock–Paczyński test, which shows that only an FRW cosmology with zero active mass is consistent with the latest model-independent baryon acoustic oscillation data.
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