3,534 research outputs found
A -partite entanglement measure of -partite quantum states
The concept of \textquotedblleft the permutationally invariant part of a
density matrx\textquotedblright constitutes an important tool for entanglement
characterization of multiqubit systems. In this paper, we first present
-partite entanglement measure of -partite quantum system, which
possesses desirable properties of an entanglement measure. Moreover, we give
strong bounds on this measure by considering the permutationally invariant part
of a multipartite state. We give two definitions of efficient measurable degree
of -partite entanglement. Finally, several concrete examples are given
to illustrate the effectiveness of our results
Multidimensional Taylor Network Optimal Control of MIMO Nonlinear Systems without Models for Tracking by Output Feedback
The actual controlled objects are generally multi-input and multioutput (MIMO) nonlinear systems with imprecise models or even without models, so it is one of the hot topics in the control theory. Due to the complex internal structure, the general control methods without models tend to be based on neural networks. However, the neuron of neural networks includes the exponential function, which contributes to the complexity of calculation, making the neural network control unable to meet the real-time requirements. The newly developed multidimensional Taylor network (MTN) requires only addition and multiplication, so it is easy to realize real-time control. In the present study, the MTN approach is extended to MIMO nonlinear systems without models to realize adaptive output feedback control. The MTN controller is proposed to guarantee the stability of the closed-loop system. Our experimental results show that the output signals of the system are bounded and the tracking error goes nearly to zero. The MTN optimal controller is proven to promise far better real-time dynamic performance and robustness than the BP neural network self-adaption reconstitution controller
Itinerant quantum critical point with frustration and non-Fermi-liquid
Employing the self-learning quantum Monte Carlo algorithm, we investigate the
frustrated transverse-field triangle-lattice Ising model coupled to a Fermi
surface. Without fermions, the spin degrees of freedom undergoes a second-order
quantum phase transition between paramagnetic and clock-ordered phases. This
quantum critical point (QCP) has an emergent U(1) symmetry and thus belongs to
the (2+1)D XY universality class. In the presence of fermions, spin
fluctuations introduce effective interactions among fermions and distort the
bare Fermi surface towards an interacting one with hot spots and Fermi pockets.
Near the QCP, non-Fermi-liquid behavior are observed at the hot spots, and the
QCP is rendered into a different universality with Hertz-Millis type exponents.
The detailed properties of this QCP and possibly related experimental systems
are also discussed.Comment: 9 pages, 8 figure
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