34 research outputs found
Optimal Phonon-to-Spin Mapping in a system of a trapped ion
We propose a protocol for measurement of the phonon number distribution of a
harmonic oscillator based on selective mapping to a discrete spin-1/2 degree of
freedom. We consider a system of a harmonically trapped ion, where a transition
between two long lived states can be driven with resolved motional sidebands.
The required unitary transforms are generated by amplitude-modulated
polychromatic radiation fields, where the time-domain ramps are obtained from
numerical optimization by application of the Chopped RAndom Basis (CRAB)
algorithm. We provide a detailed analysis of the scaling behavior of the
attainable fidelities and required times for the mapping transform with respect
to the size of the Hilbert space. As one application we show how the mapping
can be employed as a building block for experiments which require measurement
of the work distribution of a quantum process
A single ion as a shot noise limited magnetic field gradient probe
It is expected that ion trap quantum computing can be made scalable through
protocols that make use of transport of ion qubits between sub-regions within
the ion trap. In this scenario, any magnetic field inhomogeneity the ion
experiences during the transport, may lead to dephasing and loss of fidelity.
Here we demonstrate how to measure, and compensate for, magnetic field
gradients inside a segmented ion trap, by transporting a single ion over
variable distances. We attain a relative magnetic field sensitivity of \Delta
B/B_0 ~ 5*10^{-7} over a test distance of 140 \micro m, which can be extended
to the mm range, still with sub \micro m resolution. A fast experimental
sequence is presented, facilitating its use as a magnetic field gradient
calibration routine, and it is demonstrated that the main limitation is the
quantum shot noise.Comment: 5 pages, 3 figure
Trapped atoms in spatially-structured vector light fields
Spatially-structured laser beams, eventually carrying orbital angular
momentum, affect electronic transitions of atoms and their motional states in a
complex way. We present a general framework, based on the spherical tensor
decomposition of the interaction Hamiltonian, for computing atomic transition
matrix elements for light fields of arbitrary spatial mode and polarization
structures. We study both the bare electronic matrix elements, corresponding to
transitions with no coupling to the atomic center-of-mass motion, as well as
the matrix elements describing the coupling to the quantized atomic motion in
the resolved side-band regime. We calculate the spatial dependence of
electronic and motional matrix elements for tightly focused Hermite-Gaussian,
Laguerre-Gaussian and for radially and azimuthally polarized beams. We show
that near the diffraction limit, all these beams exhibit longitudinal fields
and field gradients, which strongly affect the selection rules and could be
used to tailor the light-matter interaction. The presented framework is useful
for describing trapped atoms or ions in spatially-structured light fields and
therefore for designing new protocols and setups in quantum optics, -sensing
and -information processing