7 research outputs found
Transport of charged particles by adjusting rf voltage amplitudes
We propose a planar architecture for scalable quantum information processing
(QIP) that includes X-junctions through which particles can move without
micromotion. This is achieved by adjusting radio frequency (rf) amplitudes to
move an rf null along the legs of the junction. We provide a proof-of-principle
by transporting dust particles in three dimensions via adjustable rf potentials
in a 3D trap. For the proposed planar architecture, we use regularization
techniques to obtain amplitude settings that guarantee smooth transport through
the X-junction.Comment: 16 pages, 10 figure
Quantum computing implementations with neutral particles
We review quantum information processing with cold neutral particles, that
is, atoms or polar molecules. First, we analyze the best suited degrees of
freedom of these particles for storing quantum information, and then we discuss
both single- and two-qubit gate implementations. We focus our discussion mainly
on collisional quantum gates, which are best suited for atom-chip-like devices,
as well as on gate proposals conceived for optical lattices. Additionally, we
analyze schemes both for cold atoms confined in optical cavities and hybrid
approaches to entanglement generation, and we show how optimal control theory
might be a powerful tool to enhance the speed up of the gate operations as well
as to achieve high fidelities required for fault tolerant quantum computation.Comment: 19 pages, 12 figures; From the issue entitled "Special Issue on
Neutral Particles
Suitability of linear quadrupole ion traps for large Coulomb crystals
Growing and studying large Coulomb crystals, composed of tens to hundreds of
thousands of ions, in linear quadrupole ion traps presents new challenges for
trap implementation. We consider several trap designs, first comparing the
total driven micromotion amplitude as a function of location within the
trapping volume; total micromotion is an important point of comparison since it
can limit crystal size by transfer of radiofrequency drive energy into thermal
energy. We also compare the axial component of micromotion, which leads to
first-order Doppler shifts along the preferred spectroscopy axis in precision
measurements on large Coulomb crystals. Finally, we compare trapping potential
anharmonicity, which can induce nonlinear resonance heating by shifting normal
mode frequencies onto resonance as a crystal grows. We apply a non-deforming
crystal approximation for simple calculation of these anharmonicity-induced
shifts, allowing a straightforward estimation of when crystal growth can lead
to excitation of different nonlinear heating resonances. In the axial
micromotion and anharmonicity points of comparison, we find significant
differences between the compared trap designs, with an original rotated-endcap
trap performing slightly better than the conventional in-line endcap trap
Layers of Cold Dipolar Molecules in the Harmonic Approximation
We consider the N-body problem in a layered geometry containing cold polar
molecules with dipole moments that are polarized perpendicular to the layers. A
harmonic approximation is used to simplify the hamiltonian and bound state
properties of the two-body inter-layer dipolar potential are used to adjust
this effective interaction. To model the intra-layer repulsion of the polar
molecules, we introduce a repulsive inter-molecule potential that can be
parametrically varied. Single chains containing one molecule in each layer, as
well as multi-chain structures in many layers are discussed and their energies
and radii determined. We extract the normal modes of the various systems as
measures of their volatility and eventually of instability, and compare our
findings to the excitations in crystals. We find modes that can be classified
as either chains vibrating in phase or as layers vibrating against each other.
The former correspond to acoustic and the latter to optical phonons.
Instabilities can occur for large intra-layer repulsion and produce diverging
amplitudes of molecules in the outer layers. Lastly, we consider experimentally
relevant regimes to observe the structures.Comment: 17 pages, 20 figures, accepted versio