37,826 research outputs found
The structure and magnetism of graphone
Graphone is a half-hydrogenated graphene. The structure of graphone is
illustrated as trigonal adsorption of hydrogen atoms on graphene at first.
However, we found the trigonal adsorption is unstable. We present an
illustration in detail to explain how a trigonal adsorption geometry evolves
into a rectangular adsorption geometry. We check the change of magnetism during
the evolution of geometry by evaluating the spin polarization of the
intermediate geometries. We prove and clarify that the rectangular adsorption
of hydrogen atoms on graphene is the most stable geometry of graphone and
graphone is actually antiferromagnetic.Comment: 11 pages, 4 figure
Preparation of cluster states and W states with superconducting- quantum-interference-device qubits in cavity QED
We propose schemes to create cluster states and W states by many
superconducting-quantum-interference-device (SQUID) qubits in cavities under
the influence of the cavity decay. Our schemes do not require auxiliary qubits,
and the excited levels are only virtually coupled throughout the scheme, which
could much reduce the experimental challenge. We consider the cavity decay in
our model and analytically demonstrate its detrimental influence on the
prepared entangled states.Comment: 6 pages, 3 figures, to appear in Phys. Rev.
Universal quantum computation with electronic qubits in decoherence-free subspace
We investigate how to carry out universal quantum computation
deterministically with free electrons in decoherence-free subspace by using
polarizing beam splitters, charge detectors, and single-spin rotations. Quantum
information in our case is encoded in spin degrees of freedom of the
electron-pairs which construct a decoherence-free subspace. We design building
blocks for two noncommutable single-logic-qubit gates and a logic controlled
phase gate, based on which a universal and scalable quantum information
processing robust to dephasing is available in a deterministic way.Comment: 14 pages, 3 figure
Experimentally realizable control fields in quantum Lyapunov control
As a hybrid of techniques from open-loop and feedback control, Lyapunov
control has the advantage that it is free from the measurement-induced
decoherence but it includes the system's instantaneous message in the control
loop. Often, the Lyapunov control is confronted with time delay in the control
fields and difficulty in practical implementations of the control. In this
paper, we study the effect of time-delay on the Lyapunov control, and explore
the possibility of replacing the control field with a pulse train or a
bang-bang signal. The efficiency of the Lyapunov control is also presented
through examining the convergence time of the controlled system. These results
suggest that the Lyapunov control is robust gainst time delay, easy to realize
and effective for high-dimensional quantum systems
Parametric Nanomechanical Amplification at Very High Frequency
Parametric resonance and amplification are important in both fundamental physics and technological applications. Here we report very high frequency (VHF) parametric resonators and mechanical-domain amplifiers based on nanoelectromechanical systems (NEMS). Compound mechanical nanostructures patterned by multilayer, top-down nanofabrication are read out by a novel scheme that parametrically modulates longitudinal stress in doubly clamped beam NEMS resonators. Parametric pumping and signal amplification are demonstrated for VHF resonators up to ~ 130 MHz and provide useful enhancement of both resonance signal amplitude and quality factor. We find that Joule heating and reduced thermal conductance in these nanostructures ultimately impose an upper limit to device performance. We develop a theoretical model to account for both the parametric response and nonequilibrium thermal transport in these composite nanostructures. The results closely conform to our experimental observations, elucidate the frequency and threshold-voltage scaling in parametric VHF NEMS resonators and sensors, and establish the ultimate sensitivity limits of this approach
Generalized pairwise z-complementary codes
An approach to generate generalized pairwise Z-complementary (GPZ) codes, which works in pairs in order to offer a zero correlation zone (ZCZ) in the vicinity of zero phase shift and fit extremely well in power efficient quadrature carrier modems, is introduced in this letter. Each GPZ code has MK sequences, each of length 4NK, whereMis the number of Z-complementary mates,
K is a factor to perform Walsh–Hadamard expansions, and N is the sequence length of the Z-complementary code. The proposed GPZ codes include the generalized pairwise complementary (GPC)codes as special cases
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