3,034 research outputs found
Geometric quantum gates via dark paths in Rydberg atoms
Nonadiabatic holonomic quantum computation provided a promising method to
construct high-speed geometric quantum gates. It is featured with a
near-perfect resilience to external noises, yet is found to be susceptible to
systematic errors. The latter could be partially relieved by the dark-path
scheme in the closed-system scenario. Based on an effective four-level
configuration, we here construct a universal set of nonadiabatic holonomic
controlled gates via dark paths in Rydberg atoms. Distinct from the existing
dark-path scheme, our gates can be conveniently realized and manipulated by the
off-resonant driving fields on both control atom and target atom. The driving
on the control atom can enhance significantly the robustness of the quantum
gates against systematic errors while maintaining the resilience to external
noises. Our scheme can be straightforwardly generalized to the -qubit
situation. And the three-qubit gate is less susceptible to errors than the
double-qubit one
Magnon blockade in magnon-qubit systems
A hybrid system established by the direct interaction between a magnon mode
and a superconducting transmon qubit is used to realize a high-degree blockade
for magnon. It is a fundamental way toward quantum manipulation at the level of
a single magnon and preparation of single magnon sources. Through weakly
driving the magnon and probing the qubit, our magnon-blockade proposal can be
optimized when the transversal coupling strength between the magnon and qubit
is equivalent to the detuning of the qubit and the probing field or that of the
magnon and the driving field. Under this condition, the equal-time second-order
correlation function can be analytically minimized when the
probing intensity is about three times the driving intensity. Moreover, the
magnon blockade could be further enhanced by proper driving intensity and
system decay rate, whose magnitudes outrange the current systems of cavity QED
and cavity optomechanics. In particular, the correlation function achieves
, about two orders lower than that for the photon
blockade in cavity optomechanics. Also, we discuss the effects on
from thermal noise and the extra longitudinal interaction between the magnon
and qubit. Our optimized conditions for blockade are found to persist in these
nonideal situations
Analytical modeling of surface roughness in precision grinding of particle reinforced metal matrix composites considering nanomechanical response of material
On the Electrostatics of Pneumatic Conveying of Granular Materials
In this work the electrostatics of the pneumatic conveying of granular materials in a non-conducting (PVC) vertical pipe is studied using Electrical Capacitance Tomography (ECT) system. The non-conducting wall in general attains static charges arising from particle-wall collisions in the initial periods of conveying process and then reaches equilibrium with the surroundings. The polarity of particles and conveying pipe inner wall agrees reasonably well with the contact potential difference measurements. The perturbations in the capacitance signal due to charge accumulation are larger with smaller air superficial velocity. The denser flow regimes give larger wall residual charge. Wall charging process shows similar trend by surface potential and ECT measurements. The addition of small amount (0.5% by weight) of anti-static agent (Larostat-519) in the powder form decreases the electrostatic charge generation by altering the patterns for particle-particle and particle-wall collisions.Singapore-MIT Alliance (SMA
Dilute magnetic semiconductor and half metal behaviors in 3d transition-metal doped black and blue phosphorenes: a first-principles study
We present first-principles density-functional calculations for the
structural, electronic, and magnetic properties of substitutional 3d transition
metal (TM) impurities in two-dimensional black and blue phosphorenes. We find
that the magnetic properties of such substitutional impurities can be
understood in terms of a simple model based on the Hund's rule. The TM-doped
black phosphorenes with Ti, V, Cr, Mn, Fe and Ni impurities show dilute
magnetic semiconductor (DMS) properties while those with Sc and Co impurities
show nonmagnetic properties. On the other hand, the TM-doped blue phosphorenes
with V, Cr, Mn and Fe impurities show DMS properties, those with Ti and Ni
impurities show half-metal properties, whereas Sc and Co doped systems show
nonmagnetic properties. We identify two different regimes depending on the
occupation of the hybridized electronic states of TM and phosphorous atoms: (i)
bonding states are completely empty or filled for Sc- and Co-doped black and
blue phosphorenes, leading to non-magnetic; (ii) non-bonding d states are
partially occupied for Ti-, V-, Cr-, Mn-, Fe- and Ni-doped black and blue
phosphorenes, giving rise to large and localized spin moments. These results
provide a new route for the potential applications of dilute magnetic
semiconductor and half-metal in spintronic devices by employing black and blue
phosphorenes.Comment: 9 pages, 7 figure
Numerical approximation of a phase-field surfactant model with fluid flow
Modelling interfacial dynamics with soluble surfactants in a multiphase
system is a challenging task. Here, we consider the numerical approximation of
a phase-field surfactant model with fluid flow. The nonlinearly coupled model
consists of two Cahn-Hilliard-type equations and incompressible Navier-Stokes
equation. With the introduction of two auxiliary variables, the governing
system is transformed into an equivalent form, which allows the nonlinear
potentials to be treated efficiently and semi-explicitly. By certain subtle
explicit-implicit treatments to stress and convective terms, we construct first
and second-order time marching schemes, which are extremely efficient and
easy-to-implement, for the transformed governing system. At each time step, the
schemes involve solving only a sequence of linear elliptic equations, and
computations of phase-field variables, velocity and pressure are fully
decoupled. We further establish a rigorous proof of unconditional energy
stability for the first-order scheme. Numerical results in both two and three
dimensions are obtained, which demonstrate that the proposed schemes are
accurate, efficient and unconditionally energy stable. Using our schemes, we
investigate the effect of surfactants on droplet deformation and collision
under a shear flow, where the increase of surfactant concentration can enhance
droplet deformation and inhibit droplet coalescence
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