44 research outputs found
Fast shuttling of a trapped ion in the presence of noise
We theoretically investigate the motional excitation of a single ion caused
by spring-constant and position uctuations of a harmonic trap during trap
shuttling processes. A detailed study of the sensitivity on noise for several
transport protocols and noise spectra is provided. The effect of slow
spring-constant drifts is also analyzed. Trap trajectories that minimize the
excitation are designed combining invariant-based inverse engineering,
perturbation theory, and optimal control
Quantum gate in the decoherence-free subspace of trapped ion qubits
We propose a geometric phase gate in a decoherence-free subspace with trapped
ions. The quantum information is encoded in the Zeeman sublevels of the
ground-state and two physical qubits to make up one logical qubit with ultra
long coherence time. Single- and two-qubit operations together with the
transport and splitting of linear ion crystals allow for a robust and
decoherence-free scalable quantum processor. For the ease of the phase gate
realization we employ one Raman laser field on four ions simultaneously, i.e.
no tight focus for addressing. The decoherence-free subspace is left neither
during gate operations nor during the transport of quantum information.Comment: 6 pages, 6 figure
Precise Experimental Investigation of Eigenmodes in a Planar Ion Crystal
The accurate characterization of eigenmodes and eigenfrequencies of
two-dimensional ion crystals provides the foundation for the use of such
structures for quantum simulation purposes. We present a combined experimental
and theoretical study of two-dimensional ion crystals. We demonstrate that
standard pseudopotential theory accurately predicts the positions of the ions
and the location of structural transitions between different crystal
configurations. However, pseudopotential theory is insufficient to determine
eigenfrequencies of the two-dimensional ion crystals accurately but shows
significant deviations from the experimental data obtained from resolved
sideband spectroscopy. Agreement at the level of 2.5 x 10^(-3) is found with
the full time-dependent Coulomb theory using the Floquet-Lyapunov approach and
the effect is understood from the dynamics of two-dimensional ion crystals in
the Paul trap. The results represent initial steps towards an exploitation of
these structures for quantum simulation schemes.Comment: 5 pages, 4 figures, supplemental material (mathematica and matlab
files) available upon reques
Controlling the transport of an ion: Classical and quantum mechanical solutions
We investigate the performance of different control techniques for ion
transport in state-of-the-art segmented miniaturized ion traps. We employ
numerical optimization of classical trajectories and quantum wavepacket
propagation as well as analytical solutions derived from invariant based
inverse engineering and geometric optimal control. We find that accurate
shuttling can be performed with operation times below the trap oscillation
period. The maximum speed is limited by the maximum acceleration that can be
exerted on the ion. When using controls obtained from classical dynamics for
wavepacket propagation, wavepacket squeezing is the only quantum effect that
comes into play for a large range of trapping parameters. We show that this can
be corrected by a compensating force derived from invariant based inverse
engineering, without a significant increase in the operation time
Focusing a deterministic single-ion beam
We focus down an ion beam consisting of single 40Ca+ ions to a spot size of a
few mum using an einzel-lens. Starting from a segmented linear Paul trap, we
have implemented a procedure which allows us to deterministically load a
predetermined number of ions by using the potential shaping capabilities of our
segmented ion trap. For single-ion loading, an efficiency of 96.7(7)% has been
achieved. These ions are then deterministically extracted out of the trap and
focused down to a 1sigma-spot radius of (4.6 \pm 1.3)mum at a distance of 257mm
from the trap center. Compared to former measurements without ion optics, the
einzel-lens is focusing down the single-ion beam by a factor of 12. Due to the
small beam divergence and narrow velocity distribution of our ion source,
chromatic and spherical aberration at the einzel-lens is vastly reduced,
presenting a promising starting point for focusing single ions on their way to
a substrate.Comment: 16 pages, 7 figure