41,519 research outputs found

    Pulse Width Modulation for Speeding Up Quantum Optimal Control Design

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    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 33-qubit and 66-qubit systems, and demonstrate its efficiency advantage compared with basic GRAPE algorithm

    BPS M2M2-branes in AdS4Γ—Q1,1,1AdS_4\times Q^{1, 1, 1} Dual to Loop Operators

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    In this paper, we first compute the Killing spinors of AdS4Γ—Q1,1,1AdS_4\times Q^{1, 1, 1} and its certain orbifolds. Based on this, two classes of M2M2-brane solutions are found. The first class of solutions includes M2M2-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

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    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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