-
[show abstract]
[hide abstract]
ABSTRACT: Samples of ultracold ^{174}Yb^{+} ions, confined in a linear radio-frequency Paul trap, are heated via micromotion interruption, while their temperature, density, and therefore structural phase are monitored and simulated. The observed time evolution of the ion temperature is compared to a theoretical model for ion-ion heating allowing a direct measurement of the Coulomb logarithm in a linear Paul trap. This result permits a simple, yet accurate, analytical description of ion cloud thermodynamic properties, e.g., density, temperature, and structural phase, as well as suggests limits to and improvements for ongoing trapped-ion quantum information efforts.
Physical Review Letters 04/2013; 110(17):173003. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Compared with atoms, molecules have a rich internal structure that offers many opportunities for technological and scientific advancement. The study of this structure could yield critical insights into quantum chemistry, new methods for manipulating quantum information, and improved tests of discrete symmetry violation and fundamental constant variation. Harnessing this potential typically requires the preparation of cold molecules in their quantum rovibrational ground state. However, the molecular internal structure severely complicates efforts to produce such samples. Removal of energy stored in long-lived vibrational levels is particularly problematic because optical transitions between vibrational levels are not governed by strict selection rules, which makes laser cooling difficult. Additionally, traditional collisional, or sympathetic, cooling methods are inefficient at quenching molecular vibrational motion. Here we experimentally demonstrate that the vibrational motion of trapped BaCl(+) molecules is quenched by collisions with ultracold calcium atoms at a rate comparable to the classical scattering, or Langevin, rate. This is over four orders of magnitude more efficient than traditional sympathetic cooling schemes. The high cooling rate, a consequence of a strong interaction potential (due to the high polarizability of calcium), along with the low collision energies involved, leads to molecular samples with a vibrational ground-state occupancy of at least 90 per cent. Our demonstration uses a novel thermometry technique that relies on relative photodissociation yields. Although the decrease in vibrational temperature is modest, with straightforward improvements it should be possible to produce molecular samples with a vibrational ground-state occupancy greater than 99 per cent in less than 100 milliseconds. Because sympathetic cooling of molecular rotational motion is much more efficient than vibrational cooling in traditional systems, we expect that the method also allows efficient cooling of the rotational motion of the molecules. Moreover, the technique should work for many different combinations of ultracold atoms and molecules.
Nature 03/2013; 495(7442):490-4. · 36.28 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A low-threshold solid-state UV laser using a whispering gallery mode (WGM) resonator constructed from UV transparent crystalline material is demonstrated. Using a Ce<sup>3+</sup>:LiCaAlF<sub>6</sub> resonator, we observe broad bandwidth lasing (280-330 nm) with a low threshold intensity of 7.5×10<sup>9</sup> W/m<sup>2</sup> and an effective slope efficiency of ∼25%. The lasing time delay dynamics in the pulsed operation mode are also observed and analyzed. Additionally, a LiCaAlF<sub>6</sub> WGM resonator with Q=2×10<sup>7</sup> at 370 nm is realized. The combination of this high Q and the small WGM mode volume significantly lowers the pump power threshold compared to traditional cavity designs, opening the door for both tunable continuous-wave and mode-locked operation.
Optics Letters 12/2012; 37(23):4961-3. · 3.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The role of electronic excitation in inelastic collisions between ultracold Ca atoms and Ba^{+} ions, confined in a hybrid trap, is studied for the first time. Unlike previous investigations, this system is energetically precluded from undergoing inelastic collisions in its ground state, allowing a relatively simple experimental determination and interpretation of the influence of electronic excitation. It is found that while the electronic state of the ion can critically influence the inelastic collision rate, the polarizability mismatch of the neutral atom electronic states suppresses short-range collisions, and thus inelastic processes, involving electronically excited neutral atoms. As a result of these features, it is experimentally demonstrated that it is possible to mitigate inelastic collision loss mechanisms in these systems, marking an important step toward long-lived hybrid atom-ion devices.
Physical Review Letters 11/2012; 109(22):223002. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The role of electronic excitation in charge exchange chemical reactions
between ultracold Ca atoms and Ba$^+$ ions, confined in a hybrid trap, is
studied. This prototypical system is energetically precluded from reacting in
its ground state, allowing a particularly simple interpretation of the
influence of electronic excitation. It is found that while electronic
excitation of the ion can critically influence the chemical reaction rate,
electronic excitation of the neutral atom is less important. It is also
experimentally demonstrated that with the correct choice of the atom-ion pair,
it is possible to mitigate the unwanted effects of these chemical reactions in
ultracold atom-ion environments, marking an important step towards the next
generation of hybrid devices.
05/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the integration of a linear quadrupole trap with a simple time-of-flight mass spectrometer with medium-mass resolution (m/Δm ∼ 50) geared towards the demands of atomic, molecular, and chemical physics experiments. By utilizing a novel radial ion extraction scheme from the linear quadrupole trap into the mass analyzer, a device with large trap capacity and high optical access is realized without sacrificing mass resolution. This provides the ability to address trapped ions with laser light and facilitates interactions with neutral background gases prior to analyzing the trapped ions. Here, we describe the construction and implementation of the device as well as present representative ToF spectra. We conclude by demonstrating the flexibility of the device with proof-of-principle experiments that include the observation of molecular-ion photodissociation and the measurement of trapped-ion chemical reaction rates.
The Review of scientific instruments 04/2012; 83(4):043103. · 1.52 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the implementation of a simple time-of-flight (ToF) mass
spectrometer with medium-mass resolution ($m/\Delta m\sim50$) geared towards
the demands of atomic, molecular, and chemical physics experiments. By
utilizing a novel radial ion extraction scheme from a linear quadrupole trap, a
device with large trap capacity and high optical access is realized without
sacrificing mass resolution. Here we describe the construction and
implementation of the device as well as present representative ToF spectra. We
conclude by demonstrating the flexibility of the device with proof-of-principle
experiments that include the observation of molecular-ion photodissociation and
the measurement of trapped-ion chemical reaction rates.
02/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: Optical spectroscopy of an atomic nucleus: Progress toward direct observation of the 229 Th isomer transition, Journal of Luminescence, doi:10.1016/j.jlumin.2011.09.037 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Luminescence 01/2012; · 2.10 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Ultracold 174Yb+ ions and 40Ca atoms are confined in a hybrid trap. The charge exchange chemical reaction rate constant between these two species is measured and found to be 4 orders of magnitude larger than recent measurements in other heteronuclear systems. The structure of the CaYb+ molecule is determined and used in a calculation that explains the fast chemical reaction as a consequence of strong radiative charge transfer. A possible explanation is offered for the apparent contradiction between typical theoretical predictions and measurements of the radiative association process in this and other recent experiments.
Physical Review Letters 12/2011; 107(24):243201. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The formation of (40)Ca(2)(+) molecular ions is observed in a hybrid (40)Ca magneto-optical and ion trap system. The molecular ion formation process is determined to be photo-associative ionization of ultracold (40)Ca atoms. A lower bound for the two-body rate constant is found to be beta ≥ 2 ± 1 × 10(-15) cm(3) Hz. Ab initio molecular potential curves are calculated for the neutral Ca(2) and ionic Ca(2)(+) molecules and used in a model that identifies the photo-associative ionization pathway. As this technique does not require a separate photo-association laser, it could find use as a simple, robust method for producing ultracold molecular ions.
Physical Chemistry Chemical Physics 07/2011; 13(42):18859-63. · 3.57 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Interactions between cold ions and atoms have been proposed for use in
implementing quantum gates\cite{Idziaszek2007}, probing quantum
gases\cite{Sherkunov2009}, observing novel charge-transport
dynamics\cite{Cote2000}, and sympathetically cooling atomic and molecular
systems which cannot be laser cooled\cite{Smith2005,Hudson2009}. Furthermore,
the chemistry between cold ions and atoms is foundational to issues in modern
astrophysics, including the formation of stars, planets, and interstellar
clouds\cite{Smith1992}, the diffuse interstellar bands\cite{Reddy2010}, and the
post-recombination epoch of the early universe\cite{Stancil1996b}. However, as
pointed out in refs 9 and 10, both experimental data and a theoretical
description of the ion-atom interaction at low temperatures, reached in these
modern atomic physics experiments and the interstellar environment, are still
largely missing. Here we observe a chemical reaction between ultracold
$^{174}$Yb$^+$ ions and $^{40}$Ca atoms held in a hybrid trap. We measure, and
theoretically reproduce, a chemical reaction rate constant of $ \rm \bf K
=(2\pm1.3)\times10^{-10} cm^{3}s^{-1}$ for $ \rm \bf 1 mK \leq T \leq 10 K$,
four orders of magnitude higher than reported for other heteronuclear cases. We
also offer a possible explanation for the apparent contradiction between
typical theoretical predictions and measurements of the radiative association
process in this and other systems.
04/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate a simple technique for molecular ion spectroscopy. BaCl$^+$
molecular ions are trapped in a linear Paul trap in the presence of a
room-temperature He buffer gas and photodissociated by driving an electronic
transition from the ground X$^1\Sigma^+$ state to the repulsive wall of the
A$^1\Pi$ state. The photodissociation spectrum is recorded by monitoring the
induced trap loss of BaCl$^+$ ions as a function of excitation wavelength.
Accurate molecular potentials and spectroscopic constants are determined.
Comparison of the theoretical photodissociation cross-sections with the
measurement shows excellent agreement. This study represents the first
spectroscopic data for BaCl$^+$ and an important step towards the production of
ultracold ground-state molecular ions.
01/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We have recently described a novel method for the construction of a solid-state optical frequency reference based on doping $^{229}$Th into high energy band-gap crystals. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we have argued that the $^{229}$Th optical nuclear transition may be driven inside a host crystal resulting in an optical frequency reference with a short-term stability of $3\times10^{-17}<\Delta f/f <1\times10^{-15}$ at 1 s and a systematic-limited repeatability of $\Delta f/f \sim 2 \times 10^{-16}$. Improvement by $10^2-10^3$ of the constraints on the variability of several important fundamental constants also appears possible. Here we present the results of the first phase of these experiments. Specifically, we have evaluated several high energy band-gap crystals (Th:NaYF, Th:YLF, Th:LiCAF, Na$_2$ThF$_6$, LiSAF) for their suitability as a crystal host by a combination of electron beam microprobe measurements, Rutherford Backscattering, and synchrotron excitation/fluorescence measurements. These measurements have shown LiCAF to be the most promising host crystal, and using a $^{232}$Th doped LiCAF crystal, we have performed a mock run of the actual experiment that will be used to search for the isomeric transition in $^{229}$Th. This data indicates that a measurement of the transition energy with a signal to noise ratio (SNR) greater than 30:1 can be achieved at the lowest expected fluorescence rate. Comment: Eurodim Conference Proceedings
11/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: We describe a novel approach to directly measure the energy of the narrow, low-lying isomeric state in 229Th. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we argue that the 229Th optical nuclear transition may be driven inside a host crystal with a high transition Q. This technique might also allow for the construction of a solid-state optical frequency reference that surpasses the short-term stability of current optical clocks, as well as improved limits on the variability of fundamental constants. Based on analysis of the crystal lattice environment, we argue that a precision (short-term stability) of 3×10(-17)<Δf/f<1×10(-15) after 1 s of photon collection may be achieved with a systematic-limited accuracy (long-term stability) of Δf/f∼2×10(-16). Improvement by 10(2)-10(3) of the constraints on the variability of several important fundamental constants also appears possible.
Physical Review Letters 05/2010; 104(20):200802. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper describes computer modelling of thorium doping in crystalline LiCaAlF(6) and LiSrAlF(6). The study has been motivated by the interest in using these materials as hosts for (229)Th nuclei, which are being investigated for use as frequency standards. The dopant sites and form of charge compensation are obtained; this information is essential for the further development and optimization of these devices.
Journal of Physics Condensed Matter 08/2009; 21(32):325403. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper describes computer modelling of thorium doping in crystalline LiCaAlF6 and LiSrAlF6. The study has been motivated by the interest in using these materials as hosts for 229Th nuclei, which are being investigated for use as frequency standards. The dopant sites and form of charge compensation are obtained; this information is essential for the further development and optimization of these devices.
Journal of Physics Condensed Matter 07/2009; 21(32):325403. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We describe a novel approach to directly measure the energy of the narrow, low-lying isomeric state in $^{229}$Th. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we argue that the $^{229}$Th optical nuclear transition may be driven inside a host crystal with a high transition Q. This technique might also allow for the construction of a solid-state optical frequency reference that surpasses the precision of current optical clocks, as well as improved limits on the variability of fundamental constants. Based on analysis of the crystal lattice environment, we argue that a precision of $3\times10^{-17}<\Delta f/f <1\times10^{-15}$ after 1 s of photon collection may be achieved with a systematic-limited accuracy of $\Delta f/f \sim 2 \times 10^{-16}$. Improvement by $10^2-10^3$ of the constraints on the variability of several important fundamental constants also appears possible. Comment: 5 pages
05/2009;
-
Eric R. Hudson
[show abstract]
[hide abstract]
ABSTRACT: A method for decelerating a continuous beam of neutral polar molecules is theoretically demonstrated. This method utilizes non-uniform, static electric fields and regions of adiabatic population transfer to generate a mechanical force that opposes the molecular beam's velocity. By coupling this technique with dissipative trap-loading, molecular densities $\geq10^{11}$ cm$^{-3}$ are possible. When used in combination with forced evaporative cooling the proposed method may represent a viable route to quantum degeneracy for a wide-class of molecular species.
02/2009;
-
Eric R. Hudson
[show abstract]
[hide abstract]
ABSTRACT: We propose a new method for the production of ultracold molecular ions. This method utilizes sympathetic cooling due to the strong collisions between appropriately chosen molecular ions and laser-cooled neutral atoms to realize ultracold, internal ground-state molecular ions. In contrast to other experiments producing cold molecular ions, our proposed method efficiently cools both the internal and external molecular ion degrees of freedom. The availability of an ultracold, absolute ground-state sample of molecular ions would have broad impact to fields as diverse as quantum chemistry, astrophysics, and fundamental physics; and may lead to the development of a robust, scalable quantum computer.
11/2008;
-
[show abstract]
[hide abstract]
ABSTRACT: Ultracold RbCs molecules in high-lying vibrational levels of the a3Sigma+ 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. The long-range dispersion coefficients for the collision process are calculated and used in a model that accurately reproduce the observed scattering rates.
Physical Review Letters 05/2008; 100(20):203201. · 7.37 Impact Factor
