78 research outputs found
Insensitivity of the rate of ion motional heating to trap-electrode material over a large temperature range
We present measurements of trapped-ion motional-state heating rates in niobium and gold surface-electrode ion traps over a range of trap-electrode temperatures from approximately 4 K to room temperature (295 K) in a single apparatus.Using the sideband-ratio technique after resolved-sideband cooling of single ions to the motional ground state, we find low-temperature heating rates more than two orders of magnitude below the room-temperature values and approximately equal to the lowest measured heating rates in similarly sized cryogenic traps. We find similar behavior in the two very different electrode materials, suggesting that the anomalous heating process is dominated by non-material-specific surface contaminants. Through precise control of the temperature of cryopumping surfaces, we also identify conditions under which elastic collisions with the background gas can lead to an apparent steady heating rate, despite rare collisions.United States. Dept. of Defense. Assistant Secretary of Defense for Research & Engineering (United States. Air Force Contract FA8721-05-C-002
Production and state-selective detection of ultracold, ground state RbCs molecules
Using resonance-enhanced two-photon ionization, we detect ultracold,
ground-state RbCs molecules formed via photoassociation in a laser-cooled
mixture of 85Rb and 133Cs atoms. We obtain extensive bound-bound excitation
spectra of these molecules, which provide detailed information about their
vibrational distribution, as well as spectroscopic data on the RbCs ground
a^3\Sigma^+ and excited (2)^3\Sigma^+, (1)^1\Pi states. Analysis of this data
allows us to predict strong transitions from observed excited levels to the
absolute vibronic ground state of RbCs, potentially allowing the production of
stable, ultracold polar molecules at rates as large as 10^7 s^{-1}
Loading of a surface-electrode ion trap from a remote, precooled source
We demonstrate loading of ions into a surface-electrode trap (SET) from a
remote, laser-cooled source of neutral atoms. We first cool and load
neutral Sr atoms into a magneto-optical trap from an oven that
has no line of sight with the SET. The cold atoms are then pushed with a
resonant laser into the trap region where they are subsequently photoionized
and trapped in an SET operated at a cryogenic temperature of 4.6 K. We present
studies of the loading process and show that our technique achieves ion loading
into a shallow (15 meV depth) trap at rates as high as 125 ions/s while
drastically reducing the amount of metal deposition on the trap surface as
compared with direct loading from a hot vapor. Furthermore, we note that due to
multiple stages of isotopic filtering in our loading process, this technique
has the potential for enhanced isotopic selectivity over other loading methods.
Rapid loading from a clean, isotopically pure, and precooled source may enable
scalable quantum information processing with trapped ions in large, low-depth
surface trap arrays that are not amenable to loading from a hot atomic beam
Inelastic collisions of ultra-cold heteronuclear molecules in an optical trap
Ultra-cold RbCs molecules in high-lying vibrational levels of the
a ground electronic state are confined in an optical trap.
Inelastic collision rates of these molecules with both Rb and Cs atoms are
determined for individual vibrational levels, across an order of magnitude of
binding energies. A simple model for the collision process is shown to
accurately reproduce the observed scattering rates
Study of loss in superconducting coplanar waveguide resonators
Superconducting coplanar waveguide (SCPW) resonators have a wide range of
applications due to the combination of their planar geometry and high quality
factors relative to normal metals. However, their performance is sensitive to
both the details of their geometry and the materials and processes that are
used in their fabrication. In this paper, we study the dependence of SCPW
resonator performance on materials and geometry as a function of temperature
and excitation power. We measure quality factors greater than at
high excitation power and at a power comparable to that generated
by a single microwave photon circulating in the resonator. We examine the
limits to the high excitation power performance of the resonators and find it
to be consistent with a model of radiation loss. We further observe that while
in all cases the quality factors are degraded as the temperature and power are
reduced due to dielectric loss, the size of this effect is dependent on
resonator materials and geometry. Finally, we demonstrate that the dielectric
loss can be controlled in principle using a separate excitation near the
resonance frequencies of the resonator.Comment: Replacing original version. Changes made based on referee comments.
Fixed typo in equation (3) and added appendi
Scalable loading of a two-dimensional trapped-ion array
Two-dimensional arrays of trapped-ion qubits are attractive platforms for scalable quantum information processing. Sufficiently rapid reloading capable of sustaining a large array, however, remains a significant challenge. Here with the use of a continuous flux of pre-cooled neutral atoms from a remotely located source, we achieve fast loading of a single ion per site while maintaining long trap lifetimes and without disturbing the coherence of an ion quantum bit in an adjacent site. This demonstration satisfies all major criteria necessary for loading and reloading extensive two-dimensional arrays, as will be required for large-scale quantum information processing. Moreover, the already high loading rate can be increased by loading ions in parallel with only a concomitant increase in photo-ionization laser power and no need for additional atomic flux.Office of the Assistant Secretary of Defense for Research and Engineering (United States. Air Force. Contract FA8721-05-C-0002
Evidence for multiple mechanisms underlying surface electric-field noise in ion traps
Electric-field noise from ion-trap electrode surfaces can limit the fidelity of multiqubit entangling operations in trapped-ion quantum information processors and can give rise to systematic errors in trapped-ion optical clocks. The underlying mechanism for this noise is unknown, but it has been shown that the noise amplitude can be reduced by energetic ion bombardment, or “ion milling,” of the trap electrode surfaces. Using a single trapped ⁸⁸Sr⁺ ion as a sensor, we investigate the temperature dependence of this noise both before and after ex situ ion milling of the trap electrodes. Making measurements over a trap electrode temperature range of 4 K to 295 K in both sputtered niobium and electroplated gold traps, we see a marked change in the temperature scaling of the electric-field noise after ion milling: power-law behavior in untreated surfaces is transformed to Arrhenius behavior after treatment. The temperature scaling becomes material-dependent after treatment as well, strongly suggesting that different noise mechanisms are at work before and after ion milling. To constrain potential noise mechanisms, we measure the frequency dependence of the electric-field noise, as well as its dependence on ion-electrode distance, for niobium traps at room temperature both before and after ion milling. These scalings are unchanged by ion milling.National Science Foundation (U.S.) (Award DMR-14-19807)United States. Air Force Office of Scientific Research (Contract FA8721-05-C-0002
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One visual search, many memory searches: An eye-tracking investigation of hybrid search
Suppose you go to the supermarket with a shopping list of 10 items held in memory. Your shopping expedition can be seen as a combination of visual search and memory search. This is known as “hybrid search.” There is a growing interest in understanding how hybrid search tasks are accomplished. We used eye tracking to examine how manipulating the number of possible targets (the memory set size [MSS]) changes how observers (Os) search. We found that dwell time on each distractor increased with MSS, suggesting a memory search was being executed each time a new distractor was fixated. Meanwhile, although the rate of refixation increased with MSS, it was not nearly enough to suggest a strategy that involves repeatedly searching visual space for subgroups of the target set. These data provide a clear demonstration that hybrid search tasks are carried out via a “one visual search, many memory searches” heuristic in which Os examine items in the visual array once with a very low rate of refixations. For each item selected, Os activate a memory search that produces logarithmic response time increases with increased MSS. Furthermore, the percentage of distractors fixated was strongly modulated by the MSS: More items in the MSS led to a higher percentage of fixated distractors. Searching for more potential targets appears to significantly alter how Os approach the task, ultimately resulting in more eye movements and longer response times
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