10,644 research outputs found
Charge-Density-Wave Transitions of Dirac Fermions Coupled to Phonons
The spontaneous generation of charge-density-wave order in a Dirac fermion
system via the natural mechanism of electron-phonon coupling is studied in the
framework of the Holstein model on the honeycomb lattice. Using two independent
and unbiased quantum Monte Carlo methods, the phase diagram as a function of
temperature and coupling strength is determined. It features a quantum critical
point as well as a line of thermal critical points. Finite-size scaling appears
consistent with fermionic Gross-Neveu-Ising universality for the quantum phase
transition, and bosonic Ising universality for the thermal phase transition.
The critical temperature has a maximum at intermediate couplings. Our findings
motivate experimental efforts to identify or engineer Dirac systems with
sufficiently strong and tunable electron-phonon coupling.Comment: 4+3 pages, 4+2 figure
Multiplet resonance lifetimes in resonant inelastic X-ray scattering involving shallow core levels
Resonant inelastic X-ray scattering (RIXS) spectra of model copper- and
nickel-based transition metal oxides are measured over a wide range of energies
near the M-edge (h=60-80eV) to better understand the properties of
resonant scattering involving shallow core levels. Standard multiplet RIXS
calculations are found to deviate significantly from the observed spectra.
However, by incorporating the self consistently calculated decay lifetime for
each intermediate resonance state within a given resonance edge, we obtain
dramatically improved agreement between data and theory. Our results suggest
that these textured lifetime corrections can enable a quantitative
correspondence between first principles predictions and RIXS data on model
multiplet systems. This accurate model is also used to analyze resonant elastic
scattering, which displays the elastic Fano effect and provides a rough upper
bound for the core hole shake-up response time.Comment: 6 pages, 3 figure
Neural networks-based command filtering control for a table-mount experimental helicopter
This paper presents neural networks based on command filtering control method for a table-mount experimental helicopter which has three rotational degrees-of-freedom. First, the controller is designed based on backstepping technique, and further command filtering technique is used to solve the derivative of the virtual control, thereby avoiding the effects of signal noise. Secondly, the model uncertainty of the table-mount experimental helicopter's system is estimated by using neural networks. And then, Lyapunov stabilization analysis proves the stability of the table-mount experimental helicopter closedloop attitude tracking system. Finally, the experiment is carried out to clarify the effectiveness of the proposed method. (C) 2020 The Franklin Institute. Published by Elsevier Ltd. All rights reserved
Coherent Eavesdropping Attacks in Quantum Cryptography: Nonequivalence of Quantum and Classical Key Distillation
The security of a cryptographic key that is generated by communication
through a noisy quantum channel relies on the ability to distill a shorter
secure key sequence from a longer insecure one. We show that -- for protocols
that use quantum channels of any dimension and completely characterize them by
state tomography -- the noise threshold for classical advantage distillation is
substantially lower than the threshold for quantum entanglement distillation
because the eavesdropper can perform powerful coherent attacks. The earlier
claims that the two noise thresholds are identical, which were based on
analyzing incoherent attacks only, are therefore invalid.Comment: 4 pages, 1 figure; this is the detailed account for the results
Reported in quant-ph/031015
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