593 research outputs found
Enhancement of laser cooling by the use of magnetic gradients
We present a laser cooling scheme for trapped ions and atoms using a
combination of laser couplings and a magnetic gradient field. In a
Schrieffer-Wolff transformed picture, this setup cancels the carrier and blue
sideband terms completely resulting in an improved cooling behaviour compared
to standard cooling schemes (e.g. sideband cooling) and allowing cooling to the
vibrational ground state. A condition for optimal cooling rates is presented
and the cooling behaviour for different Lamb-Dicke parameters and spontaneous
decay rates is discussed. Cooling rates of one order of magnitude less than the
trapping frequency are achieved using the new cooling method. Furthermore the
scheme turns out to be robust under deviations from the optimal parameters and
moreover provides good cooling rates also in the multi particle case.Comment: 14 pages, 8 figure
Transport quantum logic gates for trapped ions
Many efforts are currently underway to build a device capable of large scale
quantum information processing (QIP). Whereas QIP has been demonstrated for a
few qubits in several systems, many technical difficulties must be overcome in
order to construct a large-scale device. In one proposal for large-scale QIP,
trapped ions are manipulated by precisely controlled light pulses and moved
through and stored in multizone trap arrays. The technical overhead necessary
to precisely control both the ion geometrical configurations and the laser
interactions is demanding. Here we propose methods that significantly reduce
the overhead on laser beam control for performing single and multiple qubit
operations on trapped ions. We show how a universal set of operations can be
implemented by controlled transport of ions through stationary laser beams. At
the same time, each laser beam can be used to perform many operations in
parallel, potentially reducing the total laser power necessary to carry out QIP
tasks. The overall setup necessary for implementing transport gates is simpler
than for gates executed on stationary ions. We also suggest a transport-based
two-qubit gate scheme utilizing microfabricated permanent magnets that can be
executed without laser light.Comment: 31 pages, 5 figures, minor improvements in figures and notation,
submitted to PR
Unitary transformation approach for the trapped ion dynamics
We present a way of treating the problem of the interaction of a single
trapped ion with laser beams based on successive aplications of unitary
transformations onto the Hamiltonian. This allows the diagonalization of the
Hamiltonian, by means of recursive relations, without performing the Lamb-Dicke
approximation.Comment: 8 page
Observing different phases for the dynamics of entanglement in an ion trap
The evolution of the entanglement between two oscillators coupled to a common
thermal environment is non-trivial. The long time limit has three qualitatively
different behaviors (phases) depending on parameters such as the temperature of
the bath ({\em Phys. Rev. Lett.} \textbf{100}, 220401). The phases include
cases with non-vanishing long-term entanglement, others with a final
disentangled state, and situations displaying an infinite sequence of events of
disappearance and revival of entanglement. We describe an experiment to realize
these different scenarios in an ion trap. The motional degrees of freedom of
two ions are used to simulate the system while the coupling to an extra
(central) ion, which is continuously laser cooled, is the gateway to a
decohering reservoir. The scheme proposed allows for the observation and
control of motional entanglement dynamics, and is an example of a class of
simulations of quantum open systems in the non-Markovian regime.Comment: 5 pages, 5 figure
Superfast Cooling
Currently laser cooling schemes are fundamentally based on the weak coupling
regime. This requirement sets the trap frequency as an upper bound to the
cooling rate. In this work we present a numerical study that shows the
feasibility of cooling in the strong coupling regime which then allows cooling
rates that are faster than the trap frequency with state of the art
experimental parameters. The scheme we present can work for trapped atoms or
ions as well as mechanical oscillators. It can also cool medium size ions
chains close to the ground state.Comment: 5 pages 4 figure
High fidelity transport of trapped-ion qubits through an X-junction trap array
We report reliable transport of 9Be+ ions through a 2-D trap array that
includes a separate loading/reservoir zone and an "X-junction". During
transport the ion's kinetic energy in its local well increases by only a few
motional quanta and internal-state coherences are preserved. We also examine
two sources of energy gain during transport: a particular radio-frequency (RF)
noise heating mechanism and digital sampling noise. Such studies are important
to achieve scaling in a trapped-ion quantum information processor.Comment: 4 pages, 3 figures Updated to reduce manuscript to four pages. Some
non-essential information was removed, including some waveform information
and more detailed information on the tra
Cooling the Collective Motion of Trapped Ions to Initialize a Quantum Register
We report preparation in the ground state of collective modes of motion of
two trapped 9Be+ ions. This is a crucial step towards realizing quantum logic
gates which can entangle the ions' internal electronic states. We find that
heating of the modes of relative ion motion is substantially suppressed
relative to that of the center-of-mass modes, suggesting the importance of
these modes in future experiments.Comment: 5 pages, including 3 figures. RevTeX. PDF and PostScript available at
http://www.bldrdoc.gov/timefreq/ion/qucomp/papers.htm . final (published)
version. Eq. 1 and Table 1 slightly different from original submissio
Observation of the 1S0 - 3P0 clock transition in 27Al+
We report for the first time, laser spectroscopy of the 1S0 - 3P0 clock
transition in 27Al+. A single aluminum ion and a single beryllium ion are
simultaneously confined in a linear Paul trap, coupled by their mutual Coulomb
repulsion. This coupling allows the beryllium ion to sympathetically cool the
aluminum ion, and also enables transfer of the aluminum's electronic state to
the beryllium's hyperfine state, which can be measured with high fidelity.
These techniques are applied to a measurement of the clock transition
frequency, \nu = 1 121 015 393 207 851(8) Hz. They are also used to measure the
lifetime of the metastable clock state, \tau = 20.6 +/- 1.4 s, the ground state
1S0 g-factor, g_S = -0.00079248(14), and the excited state 3P0 g-factor, g_P =
-0.00197686(21), in units of the Bohr magneton.Comment: 4 pages, 2 figures; updated author lis
Fast cooling of trapped ions using the dynamical Stark shift
Published versio
Preparation of Dicke States in an Ion Chain
We have investigated theoretically and experimentally a method for preparing
Dicke states in trapped atomic ions. We consider a linear chain of ion
qubits that is prepared in a particular Fock state of motion, . The
phonons are removed by applying a laser pulse globally to the qubits, and
converting the motional excitation to flipped spins. The global nature of
this pulse ensures that the flipped spins are shared by all the target ions
in a state that is a close approximation to the Dicke state \D{N}{m}. We
calculate numerically the fidelity limits of the protocol and find small
deviations from the ideal state for and . We have demonstrated
the basic features of this protocol by preparing the state \D{2}{1} in two
Mg target ions trapped simultaneously with an Al
ancillary ion.Comment: 5 pages, 2 figure
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