43,140 research outputs found
Pulse Width Modulation for Speeding Up Quantum Optimal Control Design
This paper focuses on accelerating quantum optimal control design for complex
quantum systems. Based on our previous work [{arXiv:1607.04054}], we combine
Pulse Width Modulation (PWM) and gradient descent algorithm into solving
quantum optimal control problems, which shows distinct improvement of
computational efficiency in various cases. To further apply this algorithm to
potential experiments, we also propose the smooth realization of the optimized
control solution, e.g. using Gaussian pulse train to replace rectangular
pulses. Based on the experimental data of the D-Norleucine molecule, we
numerically find optimal control functions in -qubit and -qubit systems,
and demonstrate its efficiency advantage compared with basic GRAPE algorithm
BPS -branes in Dual to Loop Operators
In this paper, we first compute the Killing spinors of and its certain orbifolds. Based on this, two classes of -brane
solutions are found. The first class of solutions includes -branes dual to
Wilson loops in the fundamental representation as special cases. The second
class includes the candidates of the holographic description of vortex loops in
the dual field theories.Comment: v6, typoes fixed, 14 pages, no figure
Extended Bose-Hubbard model with pair tunneling: spontaneous symmetry breaking, effective ground state and fragmentation
The extended Bose-Hubbard model for a double-well potential with pair
tunneling is studied through both exact diagonalization and mean field theory
(MFT). When pair tunneling is strong enough, the ground state wavefunction
predicted by the MFT is complex and doubly degenerate while the quantum ground
state wavefunction is always real and unique. The time reversal symmetry is
spontaneously broken when the system transfers from the quantum ground state
into one of the mean field ground states upon a small perturbation. As the gap
between the lowest two levels decreases exponentially with particle number, the
required perturbation inducing the spontaneous symmetry breaking (SSB) is
infinitesimal for particle number of typical cold atom systems. The quantum
ground state is further analyzed with the Penrose-Onsager criterion, and is
found to be a fragmented condensate. The state also develops the pair
correlation and has non-vanishing pair order parameter instead of the
conventional single particle order parameter. When this model is generalized to
optical lattice, a pair superfluid can be generated. The mean field ground
state can be regarded as effective ground state in this simple model. The
detailed computation for this model enables us to offer an in-depth discussion
of the relation between SSB and effective ground state, giving a glimpse on how
nonlinearity arises in the SSB of a quantum system.Comment: 6 pages, 6 figure
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