1,983 research outputs found
Robust nonadiabatic geometric quantum computation by dynamical correction
Besides the intrinsic noise resilience property, nonadiabatic geometric
phases are of the fast evolution nature, and thus can naturally be used in
constructing quantum gates with excellent performance, i.e., the so-called
nonadiabatic geometric quantum computation (NGQC). However, previous
single-loop NGQC schemes are sensitive to the operational control error, i.e.,
the error, due to the limitations of the implementation. Here, we propose a
robust scheme for NGQC combining with the dynamical correction technique, which
still uses only simplified pulses, and thus being experimental friendly. We
numerically show that our scheme can greatly improve the gate robustness in
previous protocols, retaining the intrinsic merit of geometric phases.
Furthermore, to fight against the dephasing noise, due to the error, we can
incorporate the decoherence-free subspace encoding strategy. In this way, our
scheme can be robust against both types of errors. Finally, we also propose how
to implement the scheme with encoding on superconducting quantum circuits with
experimentally demonstrated technology. Therefore, due to the intrinsic
robustness, our scheme provides a promising alternation for the future scalable
fault-tolerant quantum computation.Comment: 6 pages, 5 figure
Time-optimal universal quantum gates on superconducting circuits
Decoherence is inevitable when manipulating quantum systems. It decreases the
quality of quantum manipulations and thus is one of the main obstacles for
large-scale quantum computation, where high-fidelity quantum gates are needed.
Generally, the longer a gate operation is, the more decoherence-induced gate
infidelity will be. Therefore, how to shorten the gate time becomes an urgent
problem to be solved. To this end, time-optimal control based on solving the
quantum brachistochrone equation is a straightforward solution. Here, based on
time-optimal control, we propose a scheme to realize universal quantum gates on
superconducting qubits in a two-dimensional square lattice configuration, and
the two-qubit gate fidelity approaches 99.9\%. Meanwhile, we can further
accelerate the Z-axis gate considerably by adjusting the detuning of the
external driving. Finally, in order to reduce the influence of the dephasing
error, decoherence-free subspace encoding is also incorporated in our physical
implementation. Therefore, we present a fast quantum scheme which is promising
for large-scale quantum computation.Comment: v2 accepte
Study of an Improved Fuzzy Direct Torque Control of Induction Motor
The conventional direct torque control will inevitably produce torque ripple because of its way of flux estimates. For the purpose of handling this problem, a new control strategy was presented in this paper. This strategy combined subdivides control with voltage vector and fuzzy logic control in traditional direct torque control. In this model, the fuzzy logic combined the phase angle of the flux, the flux error and torque error as fuzzy variables and classified these fuzzy variables, in order to optimize the choice of voltage space vector, and the same time the traditional PID regulator is replaced by a fuzzy regulator. Simulation results show that, a great improvement torque responses , a great reduction of torque ripples is achieved and the strategy has a better dynamic and steady performance, especially in low-speed area
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