4,605 research outputs found
Ising Hamiltonians for Constrained Combinatorial Optimization Problems and the Metropolis-Hastings Warm-Starting Algorithm
Quantum approximate optimization algorithm (QAOA) is a promising variational
quantum algorithm for combinatorial optimization problems. However, the
implementation of QAOA is limited due to the requirement that the problems be
mapped to Ising Hamiltonians and the nonconvex optimization landscapes.
Although the Ising Hamiltonians for many NP hard problems have been obtained, a
general method to obtain the Ising Hamiltonians for constrained combinatorial
optimization problems (CCOPs) has not yet been investigated. In this paper, a
general method is introduced to obtain the Ising Hamiltonians for CCOPs and the
Metropolis-Hastings warm-starting algorithm for QAOA is presented which can
provably converge to the global optimal solutions. The effectiveness of this
method is demonstrated by tackling the minimum weight vertex cover (MWVC)
problem, the minimum vertex cover (MVC) problem, and the maximal independent
set problem as examples. The Ising Hamiltonian for the MWVC problem is obtained
first time by using this method. The advantages of the Metropolis-Hastings
warm-starting algorithm presented here is numerically analyzed through solving
30 randomly generated MVC cases with 1-depth QAOA
TEMPERATURE ANALYSIS OF HIGH LATITUDES AND LOW ALTITUDE ISLAND PERMAFROST DURING THE CONSTRUCTION OF CFG PILE
Cement fly ash gravel (CFG) pile composite foundation is an effective and economic foundation treatment approach, which is significant to building a foundation, subgrade construction, and so forth. The present paper aims to investigate the temperature behaviours of high latitudes and low altitude island permafrost when the CFG pile was constructed, in which FEM and field temperature monitoring of permafrost was utilized. The proposed findings demonstrate that the temperature disturbance of permafrost is obvious when the CFG pile was constructed, and the temperature variation of CFG pile and permafrost in FEM has a good agreement with the results of field temperature monitoring. Additionally, the influence of different height subgrade on the temperature field of CFG pile composite foundation was analyzed by FEM. The proposed findings demonstrate that the height of subgrade affects the maximum temperature increase of permafrost and the re-frozen time of permafrost after the construction of CFG pile composite foundation
Nonlinear Improvement of Qubit-qudit Entanglement Witnesses
The entanglement witness is an important and experimentally applicable tool
for entanglement detection. In this paper, we provide a nonlinear improvement
of any entanglement witness for quantum systems. Compared with any
existing entanglement witness, the improved separability criterion only needs
two more measurements on local observables. Detailed examples are employed to
illustrate the efficiency of the nonlinear improvement for general, optimal and
non-decomposable entanglement witnesses.Comment: 11 pages, 0 figure
InAs/GaAs quantum dot laser epitaxially grown on on-axis (001) GaAsOI substrate
Quantum dot (QD) laser as a light source for silicon optical integration has attracted great research attention because of the strategic vision of optical interconnection. In this paper, the communication band InAs QD ridge waveguide lasers were fabricated on GaAs-on-insulator (GaAsOI) substrate by combining ion-slicing technique and molecular beam epitaxy (MBE) growth. On the foundation of optimizing surface treatment processes, the InAs/In0.13Ga0.87As/GaAs dot-in-well (DWELL) lasers monolithically grown on a GaAsOI substrate were realized under pulsed operation at 20 \ub0C. The static device measurements reveal comparable performance in terms of threshold current density, slope efficiency and output power between the QD lasers on GaAsOI and GaAs substrates. This work shows great potential to fabricate highly integrated light source on Si for photonic integrated circuits
Radial Angular Momentum Transfer and Magnetic Barrier for Short-Type Gamma-Ray Burst Central Engine Activity
Soft extended emission (EE) following initial hard spikes up to 100 seconds
was observed with {\em Swift}/BAT for about half of short-type gamma-ray bursts
(SGRBs). This challenges the conversional central engine models of SGRBs, i.e.,
compact star merger models. In the framework of the black hole-neutron star
merger models, we study the roles of the radial angular momentum transfer in
the disk and the magnetic barrier around the black hole for the activity of
SGRB central engines. We show that the radial angular momentum transfer may
significantly prolong the lifetime of the accretion process and multiple
episodes may be switched by the magnetic barrier. Our numerical calculations
based on the models of the neutrino-dominated accretion flows suggest that the
disk mass is critical for producing the observed EE. In case of the mass being
, our model can reproduce the observed timescale and
luminosity of both the main and EE episodes in a reasonable parameter set. The
predicted luminosity of the EE component is lower than the observed EE with
about one order of magnitude and the timescale is shorter than 20 seconds if
the disk mass being . {\em Swift}/BAT-like instruments may
be not sensitive enough to detect the EE component in this case. We argue that
the EE component would be a probe for merger process and disk formation for
compact star mergers.Comment: 9 pages, 3 figures, accepted for publication in Ap
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