63 research outputs found
Cavity sideband cooling of a single trapped ion
We report a demonstration and quantitative characterization of
one-dimensional cavity cooling of a single trapped 88Sr+ ion in the resolved
sideband regime. We measure the spectrum of cavity transitions, the rates of
cavity heating and cooling, and the steady-state cooling limit. The cavity
cooling dynamics and cooling limit of 22.5(3) motional quanta, limited by the
moderate coupling between the ion and the cavity, are consistent with a simple
model [Phys. Rev. A 64, 033405] without any free parameters, validating the
rate equation model for cavity cooling.Comment: 5 pages, 4 figure
Demonstration of a quantum logic gate in a cryogenic surface-electrode ion trap
We demonstrate quantum control techniques for a single trapped ion in a
cryogenic, surface-electrode trap. A narrow optical transition of Sr+ along
with the ground and first excited motional states of the harmonic trapping
potential form a two-qubit system. The optical qubit transition is susceptible
to magnetic field fluctuations, which we stabilize with a simple and compact
method using superconducting rings. Decoherence of the motional qubit is
suppressed by the cryogenic environment. AC Stark shift correction is
accomplished by controlling the laser phase in the pulse sequencer, eliminating
the need for an additional laser. Quantum process tomography is implemented on
atomic and motional states using conditional pulse sequences. With these
techniques we demonstrate a Cirac-Zoller Controlled-NOT gate in a single ion
with a mean fidelity of 91(1)%.Comment: 11 pages, 5 figures, 4 table
High fidelity quantum gates with ions in cryogenic microfabricated ion traps
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 135-146).While quantum information processing offers a tantalizing possibility of a significant speedup in execution of certain algorithms, as well as enabling previously unmanageable simulations of large quantum systems, it remains extremely difficult to realize experimentally. Recently, fundamental building blocks of a quantum computer, including one and two qubit gates, teleportation and error correction, were demonstrated using trapped atomic ions. Scaling to a larger number of qubits requires miniaturization of the ion traps, currently limited by the sharply increasing motional state decoherence at sub-100 [mu]m ion-electrode distances. This thesis explores the source and suppression of this decoherence at cryogenic temperatures, and demonstrates fundamental logic gates in a surface electrode ion trap. Construction of the apparatus requires the development of a number of experimental techniques. Design, numerical simulation and implementation of a surface electrode ion trap is presented. Cryogenic cooling of the trap to near 4 K is accomplished by contact with a bath cryostat. Ions are loaded by ablation or photoionization, both of which are characterized in terms of generated stray fields and heat load. The bulk of new experimental results deals with measurements of electric field noise at the ion's position. Upon cooling to 6 K, the measured rates are suppressed by up to 7 orders of magnitude, more than two orders of magnitude below previously published data for similarly sized traps operated at room temperature. The observed noise depends strongly on fabrication process, which suggests further improvements are possible. The measured dependence of the electric field noise on temperature is inconsistent with published models, and can be explained using a continuous spectrum of activated fluctuators. The fabricated surface electrode traps are used to demonstrate coherent operations and the classical control required for trapped ion quantum computation. The necessary spectral properties of coherent light sources are achieved with a novel design using optical feedback to a triangular, medium finesse, cavity, followed by electronic feedback to an ultra-high finesse reference cavity.(cont.) Single and two qubit operations on a single ion are demonstrated with classical fidelity in excess of 95%. Magnetic field gradient coils built into the trap allow for individual addressing of ions, a prerequisite to scaling to multiple qubits.by Jarosław Labaziewicz.Ph.D
Superconducting microfabricated ion traps
We fabricate superconducting ion traps with niobium and niobium nitride and
trap single 88Sr ions at cryogenic temperatures. The superconducting transition
is verified and characterized by measuring the resistance and critical current
using a 4-wire measurement on the trap structure, and observing change in the
rf reflection. The lowest observed heating rate is 2.1(3) quanta/sec at 800 kHz
at 6 K and shows no significant change across the superconducting transition,
suggesting that anomalous heating is primarily caused by noise sources on the
surface. This demonstration of superconducting ion traps opens up possibilities
for integrating trapped ions and molecular ions with superconducting devices.Comment: 3 pages, 2 figure
Individual addressing of ions using magnetic field gradients in a surface-electrode ion trap
Dense array of ions in microfabricated traps represent one possible way to
scale up ion trap quantum computing. The ability to address individual ions is
an important component of such a scheme. We demonstrate individual addressing
of trapped ions in a microfabricated surface-electrode trap using a magnetic
field gradient generated on-chip. A frequency splitting of 310(2) kHz for two
ions separated by 5 um is achieved. Selective single qubit operations are
performed on one of two trapped ions with an average of 2.2+/-1.0% crosstalk.
Coherence time as measured by the spin-echo technique is unaffected by the
field gradient.Comment: 3 pages, 3 figures; submitted to AP
Electron impact ionization loading of a surface electrode ion trap
We demonstrate a method for loading surface electrode ion traps by electron
impact ionization. The method relies on the property of surface electrode
geometries that the trap depth can be increased at the cost of more
micromotion. By introducing a buffer gas, we can counteract the rf heating
assocated with the micromotion and benefit from the larger trap depth. After an
initial loading of the trap, standard compensation techniques can be used to
cancel the stray fields resulting from charged dielectric and allow for the
loading of the trap at ultra-high vacuum.Comment: 4 pages, 5 eps figures. Shift in focus, minor correction
Suppression of Heating Rates in Cryogenic Surface-Electrode Ion Traps
Dense arrays of trapped ions provide one way of scaling up ion trap quantum
information processing. However, miniaturization of ion traps is currently
limited by sharply increasing motional state decoherence at sub-100 um
ion-electrode distances. We characterize heating rates in cryogenically cooled
surface-electrode traps, with characteristic sizes in 75 um to 150 um range.
Upon cooling to 6 K, the measured rates are suppressed by 7 orders of
magnitude, two orders of magnitude below previously published data of similarly
sized traps operated at room temperature. The observed noise depends strongly
on fabrication process, which suggests further improvements are possible.Comment: 4 pages, 4 figure
The Kondo Effect in the Presence of Magnetic Impurities
We measure transport through gold grain quantum dots fabricated using
electromigration, with magnetic impurities in the leads. A Kondo interaction is
observed between dot and leads, but the presence of magnetic impurities results
in a gate-dependent zero-bias conductance peak that is split due to an RKKY
interaction between the spin of the dot and the static spins of the impurities.
A magnetic field restores the single Kondo peak in the case of an
antiferromagnetic RKKY interaction. This system provides a new platform to
study Kondo and RKKY interactions in metals at the level of a single spin.Comment: 5 pages, 4 figure
Cryogenic Ion Trapping Systems with Surface-Electrode Traps
We present two simple cryogenic RF ion trap systems in which cryogenic
temperatures and ultra high vacuum pressures can be reached in as little as 12
hours. The ion traps are operated either in a liquid helium bath cryostat or in
a low vibration closed cycle cryostat. The fast turn around time and
availability of buffer gas cooling made the systems ideal for testing
surface-electrode ion traps. The vibration amplitude of the closed cycled
cryostat was found to be below 106 nm. We evaluated the systems by loading
surface-electrode ion traps with Sr ions using laser ablation, which
is compatible with the cryogenic environment. Using Doppler cooling we observed
small ion crystals in which optically resolved ions have a trapped lifetime
over 2500 minutes.Comment: 10 pages, 13 EPS figure
A microfabricated surface ion trap on a high-finesse optical mirror
A novel approach to optics integration in ion traps is demonstrated based on
a surface electrode ion trap that is microfabricated on top of a dielectric
mirror. Additional optical losses due to fabrication are found to be as low as
80 ppm for light at 422 nm. The integrated mirror is used to demonstrate light
collection from, and imaging of, a single 88 Sr+ ion trapped m
above the mirror.Comment: 4 pages, 3 figure
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