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Tripartite Entanglement Measures of Generalized GHZ State in Uniform Acceleration
Qian Dong, M. A. Mercado Sanchez, Guo-Hua Sun, Mohamad Toutounji, Shi-Hai Dong
Chin. Phys. Lett. 2019, 36 (10):
100301
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DOI: 10.1088/0256-307X/36/10/100301
Using the single-mode approximation, we study entanglement measures including two independent quantities; i.e., negativity and von Neumann entropy for a tripartite generalized Greenberger–Horne–Zeilinger (GHZ) state in noninertial frames. Based on the calculated negativity, we study the whole entanglement measures named as the algebraic average $\pi_{3}$-tangle and geometric average ${\it \Pi}_{3}$-tangle. We find that the difference between them is very small or disappears with the increase of the number of accelerated qubits. The entanglement properties are discussed from one accelerated observer and others remaining stationary to all three accelerated observers. The results show that there will always exist entanglement, even if acceleration $r$ arrives to infinity. The degree of entanglement for all 1–1 tangles are always equal to zero, but 1–2 tangles always decrease with the acceleration parameter $r$. We notice that the von Neumann entropy increases with the number of the accelerated observers and $S_{\kappa_{\rm I}\zeta_{\rm I}}$ ($\kappa, \zeta\in ({\rm A, B, C})$) first increases and then decreases with the acceleration parameter $r$. This implies that the subsystem $\rho_{\kappa_{\rm I}\zeta_{\rm I}}$ is first more disorder and then the disorder will be reduced as the acceleration parameter $r$ increases. Moreover, it is found that the von Neumann entropies $S_{\rm ABCI}$, $S_{\rm ABICI}$ and $S_{\rm AIBICI}$ always decrease with the controllable angle $\theta$, while the entropies of the bipartite subsystems $S_{2-2_{\rm non}}$ (two accelerated qubits), $S_{2-1_{\rm non}}$ (one accelerated qubit) and $S_{2-0_{\rm non}}$ (without accelerated qubit) first increase with the angle $\theta$ and then decrease with it.
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Experimental Hamiltonian Learning of an 11-Qubit Solid-State Quantum Spin Register
P.-Y. Hou, L. He, F. Wang, X.-Z. Huang, W.-G. Zhang, X.-L. Ouyang, X. Wang, W.-Q. Lian, X.-Y. Chang, L.-M. Duan
Chin. Phys. Lett. 2019, 36 (10):
100303
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DOI: 10.1088/0256-307X/36/10/100303
Learning the Hamiltonian of a quantum system is indispensable for prediction of the system dynamics and realization of high fidelity quantum gates. However, it is a significant challenge to efficiently characterize the Hamiltonian which has a Hilbert space dimension exponentially growing with the system size. Here, we develop and implement an adaptive method to learn the effective Hamiltonian of an 11-qubit quantum system consisting of one electron spin and ten nuclear spins associated with a single nitrogen-vacancy center in a diamond. We validate the estimated Hamiltonian by designing universal quantum gates based on the learnt Hamiltonian and implementing these gates in the experiment. Our experimental result demonstrates a well-characterized 11-qubit quantum spin register with the ability to test quantum algorithms, and shows our Hamiltonian learning method as a useful tool for characterizing the Hamiltonian of the nodes in a quantum network with solid-state spin qubits.
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Manipulating the Flipping of Water Dipoles in Carbon Nanotubes
Dang-Xin Mao, Xiao-Gang Wang, Guo-Quan Zhou, Song-Wei Zeng, Liang Chen, Jun-Lang Chen, Chao-Qing Dai
Chin. Phys. Lett. 2019, 36 (10):
103101
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DOI: 10.1088/0256-307X/36/10/103101
Flipping of water dipoles in carbon nanotubes is of great importance in many physical and biological applications, such as signal amplification, molecular switches and nano-gates. Ahead of these applications, understanding and inhibiting the non-negligible thermal noise is essential. Here, we use molecular dynamics simulations to show that the flipping frequency of water dipoles increases with the rising temperature, and the thermal noise can be suppressed by imposed charges and external uniform electric fields. Furthermore, the water dipoles flip periodically between two equiprobable and stable states under alternating electric fields. These two stable states may be adopted to store 0 and 1 bits for memory storage or molecular computing.
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Dramatic Spectral Broadening of Ultrafast Laser Pulses in Molecular Nitrogen Ions
Jin-Ming Chen, Jin-Ping Yao, Zhao-Xiang Liu, Bo Xu, Fang-Bo Zhang, Yue-Xin Wan, Wei Chu, Zhen-Hua Wang, Ling-Ling Qiao, Ya Cheng
Chin. Phys. Lett. 2019, 36 (10):
104204
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DOI: 10.1088/0256-307X/36/10/104204
We investigate nonlinear interaction of nitrogen molecules with a two-color laser field composed by an intense 800 nm laser pulse and a weak 400 nm laser pulse. It is demonstrated that the spectrum of 400 nm pulses is dramatically broadened when the two beams temporally overlap. In comparison, the spectral broadening in argon is less pronounced, although argon atoms and nitrogen molecules have comparable ionization potentials. We reveal that the dramatic spectral broadening originates from the greatly enhanced nonlinear optical effects in the near-resonant condition of interaction between the 400 nm pulses and the nitrogen molecular ions.
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Generation of Ultrahigh-Velocity Collisionless Electrostatic Shocks Using an Ultra-Intense Laser Pulse Interacting with Foil-Gas Target
Shu-Kai He, Jin-Long Jiao, Zhi-Gang Deng, Feng Lu, Lei Yang, Fa-Qiang Zhang, Ke-Gong Dong, Wei Hong, Zhi-Meng Zhang, Bo Zhang, Jian Teng, Wei-Min Zhou, Yu-Qiu Gu
Chin. Phys. Lett. 2019, 36 (10):
105201
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DOI: 10.1088/0256-307X/36/10/105201
Ultra high-velocity collisionless shocks are generated using an ultra-intense laser interacting with foil-gas target, which consists of copper foil and helium gas. The energy of helium ions accelerated by shock and the proton probing image of the shock electrostatic field show that the shock velocity is 0.02$c$, where $c$ is the light speed. The numerical and theory studies indicate that the collisionless shock velocity exceeding 0.1$c$ can be generated by a laser pulse with picosecond duration and an intensity of 10$^{20}$ W/cm$^{2}$. This system may be relevant to the study of mildly relativistic velocity collisionless shocks in astrophysics.
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Pressure-Induced Metallization Accompanied by Elongated S–S Dimer in Charge Transfer Insulator NiS$_{2}$
Hao Wu, Yong-Hui Zhou, Yi-Fang Yuan, Chun-Hua Chen, Ying Zhou, Bo-Wen Zhang, Xu-Liang Chen, Chuan-Chuan Gu, Chao An, Shu-Yang Wang, Meng-Yao Qi, Ran-Ran Zhang, Li-Li Zhang, Xin-Jian Li, Zhao-Rong Yang
Chin. Phys. Lett. 2019, 36 (10):
107101
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DOI: 10.1088/0256-307X/36/10/107101
The insulator-metal transition triggered by pressure in charge transfer insulator NiS$_{2}$ is investigated by combining high-pressure electrical transport, synchrotron x-ray diffraction and Raman spectroscopy measurements up to 40–50 GPa. Upon compression, we show that the metallization firstly appears in the low temperature region at $\sim$3.2 GPa and then extends to room temperature at $\sim $8.0 GPa. During the insulator-metal transition, the bond length of S–S dimer extracted from the synchrotron x-ray diffraction increases with pressure, which is supported by the observation of abnormal red-shift of the Raman modes between 3.2 and 7.1 GPa. Considering the decreasing bonding-antibonding splitting due to the expansion of S–S dimer, the charge gap between the S-$pp\pi^*$ band and the upper Hubbard band of Ni-3$d$ $e_{\rm g}$ state is remarkably decreased. These results consistently indicate that the elongated S–S dimer plays a predominant role in the insulator-metal transition under high pressure, even though the $p$-$d$ hybridization is enhanced simultaneously, in accordance with a scenario of charge-gap-controlled type.
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Strong Exciton-Plasmon Coupling and Hybridization of Organic-Inorganic Exciton-Polaritons in Plasmonic Nanocavity
Ping Jiang, Chao Li, Yuan-Yuan Chen, Gang Song, Yi-Lin Wang, Li Yu
Chin. Phys. Lett. 2019, 36 (10):
107301
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DOI: 10.1088/0256-307X/36/10/107301
We investigate strong exciton-plasmon coupling and plasmon-mediated hybridization between the Frenkel (F) and Wannier–Mott (WM) excitons of an organic-inorganic hybrid system consisting of a silver ring separated from a monolayer WS$_{2}$ by J-aggregates. The extinction spectra of the hybrid system calculated by employing the coupled oscillator model are consistent with the results simulated by the finite-difference time-domain method. The calculation results show that strong couplings among F excitons, WM excitons, and localized surface plasmon resonances (LSPRs) lead to the appearance of three plexciton branches in the extinction spectra. The weighting efficiencies of the F exciton, WM exciton and LSPR modes in three plexciton branches are used to analyze the exciton-polaritons in the system. Furthermore, the strong coupling between two different excitons and LSPRs is manipulated by tuning F or WM exciton resonances.
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Broken Time-Reversal Symmetry in Superconducting Partially Filled Skutterudite Pr$_{1-\delta}$Pt$_{4}$Ge$_{12}$
Jia-Wei Zang, Jian Zhang, Zi-Hao Zhu, Zhao-Feng Ding, Kevin Huang, Xiao-Ran Peng, Adrian D. Hillier, Lei Shu
Chin. Phys. Lett. 2019, 36 (10):
107402
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DOI: 10.1088/0256-307X/36/10/107402
Time reversal symmetry (TRS) is a key symmetry for classification of unconventional superconductors, and the violation of TRS often results in a wealth of novel properties. Here we report the synthesis and superconducting properties of the partially filled skutterudite Pr$_{1-\delta}$Pt$_{4}$Ge$_{12}$. The results from x-ray diffraction and magnetization measurements show that the [Pt$_{4}$Ge$_{12}$] cage-forming structure survives and bulk superconductivity is preserved below the superconducting transition temperature $T_{\rm c}=7.80$ K. The temperature dependence of both the upper critical field and the electronic specific heat can be described in terms of a two-gap model, providing strong evidence of multi-band superconductivity. TRS breaking is observed using zero field muon-spin relaxation experiments, and the magnitude of the spontaneous field is nearly half of that in PrPt$_{4}$Ge$_{12}$.
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Neutron Powder Diffraction Study on the Non-Superconducting Phases of ThFeAsN$_{1-x}$O$_x$ ($x=0.15, 0.6$) Iron Pnictide
Hui-Can Mao, Bing-Feng Hu, Yuan-Hua Xia, Xi-Ping Chen, Cao Wang, Zhi-Cheng Wang, Guang-Han Cao, Shi-Liang Li, Hui-Qian Luo
Chin. Phys. Lett. 2019, 36 (10):
107403
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DOI: 10.1088/0256-307X/36/10/107403
We use neutron powder diffraction to study the non-superconducting phases of ThFeAsN$_{1-x}$O$_x$ with $x=0.15$, 0.6. In our previous results of the superconducting phase ThFeAsN with $T_{\rm c}=30$ K, no magnetic transition is observed by cooling down to 6 K, and possible oxygen occupancy at the nitrogen site is shown in the refinement [Europhys. Lett. 117 (2017) 57005]. Here in the oxygen doped system ThFeAsN$_{1-x}$O$_x$, two superconducting regions ($0\leqslant x \leqslant 0.1$ and $0.25\leqslant x \leqslant 0.55$) are identified by transport experiments [J. Phys.: Condens. Matter 30 (2018) 255602]. However, within the resolution of our neutron powder diffraction experiment, neither the intermediate doping $x=0.15$ nor the heavily overdoped compound $x=0.6$ shows any magnetic order from 300 K to 4 K. Therefore, while it shares the common phenomenon of two superconducting domes as most 1111-type iron-based superconductors, the magnetically ordered parent compound may not exist in this nitride family.
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Superconductivity of the FeSe/SrTiO$_{3}$ Interface in View of BCS–BEC Crossover
Shuyuan Zhang, Guangyao Miao, Jiaqi Guan, Xiaofeng Xu, Bing Liu, Fang Yang, Weihua Wang, Xuetao Zhu, Jiandong Guo
Chin. Phys. Lett. 2019, 36 (10):
107404
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DOI: 10.1088/0256-307X/36/10/107404
In paired Fermi systems, strong many-body effects exhibit in the crossover regime between the Bardeen–Cooper–Schrieffer (BCS) and the Bose–Einstein condensation (BEC) limits. The concept of the BCS–BEC crossover, which is studied intensively in the research field of cold atoms, has been extended to condensed matters. Here by analyzing the typical superconductors within the BCS–BEC phase diagram, we find that FeSe-based superconductors are prone to shift their positions in the BCS–BEC crossover regime by charge doping or substrate substitution, since their Fermi energies and the superconducting gap sizes are comparable. Especially at the interface of single-layer FeSe on SrTiO$_{3}$ substrate, the superconductivity is relocated closer to the crossover unitary than other doped FeSe-based materials, indicating that the pairing interaction is effectively modulated. We further show that hole-doping can drive the interfacial system into the phase with possible pre-paired electrons, demonstrating its flexible tunability within the BCS–BEC crossover regime.
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Numerical and Experimental Study on the Device Geometry Dependence of Performance of Heterjunction Phototransistors
Jin-Lei Lu, Chen Yue, Xuan-Zhang Li, Wen-Xin Wang, Hai-Qiang Jia, Hong Chen, Lu Wang
Chin. Phys. Lett. 2019, 36 (10):
108501
.
DOI: 10.1088/0256-307X/36/10/108501
Heterojunction phototransistors (HPTs) with scaling emitters have a higher optical gain compared to HPTs with normal emitters. However, to quantitatively describe the relationship between the emitter-absorber area ratio ($A_{\rm e}/A_{\rm a}$) and the performance of HPTs, and to find the optimum value of $A_{\rm e}/A_{\rm a}$ for the geometric structure design, we develop an analytical model for the optical gain of HPTs. Moreover, five devices with different $A_{\rm e}/A_{\rm a}$ are fabricated to verify the numerical analysis result. As is expected, the measurement result is in good agreement with the analysis model, both of them confirmed that devices with a smaller $A_{\rm e}/A_{\rm a}$ exhibit higher optical gain. The device with area ratio of 0.0625 has the highest optical gain, which is two orders of magnitude larger than that of the device with area ratio of 1 at 3 V. However, the dark current of the device with the area ratio of 0.0625 is forty times higher than that of the device with the area ratio of 1. By calculating the signal-to-noise ratios (SNRs) of the devices, the optimal value of $A_{\rm e}/A_{\rm a}$ can be obtained to be 0.16. The device with the area ratio of 0.16 has the maximum SNR. This result can be used for future design principles for high performance HPTs.
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23 articles
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