G. K. Campbell

University of Colorado at Boulder , Boulder, CO, United States

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Publications (28)82.26 Total impact

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    ABSTRACT: We describe recent progress on the JILA Sr optical frequency standard, which has a systematic uncertainty at the 10<sup>-16</sup> fractional frequency level. The dominant contributions to the systematic error are from blackbody radiation shifts and collisional shifts. We discuss the blackbody radiation shift and propose measurements and experimental protocols that should reduce its systematic contribution. We discuss how collisional frequency shifts can arise in an optical lattice clock employing fermionic atoms, and experimentally demonstrate how the uncertainty in this density-dependent correction to the clock frequency is reduced.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 04/2010; · 1.82 Impact Factor
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    ABSTRACT: We investigate the influence of atomic motion on precision Rabi spectroscopy of ultracold fermionic atoms confined in a deep, one dimensional (1D) optical lattice. We analyze the spectral components of longitudinal sideband spectra and present a model to extract information about the transverse motion and sample temperature from their structure. Rabi spectroscopy of the clock transition itself is also influenced by atomic motion in the weakly confined transverse directions of the optical lattice. By deriving Rabi flopping and Rabi lineshapes of the carrier transition, we obtain a model to quantify trap state dependent excitation inhomogeneities. The inhomogeneously excited ultracold fermions become distinguishable, which allows s-wave collisions. We derive a detailed model of this process and explain observed density shift data in terms of a dynamic mean field shift of the clock transition. Comment: 11 pages, 8 figures, to appear in Phys. Rev. A. Changes to abstract, text, and figures, new reference
    Physical Review A 06/2009; · 3.04 Impact Factor
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    ABSTRACT: At ultracold temperatures, the Pauli exclusion principle suppresses collisions between identical fermions. This has motivated the development of atomic clocks with fermionic isotopes. However, by probing an optical clock transition with thousands of lattice-confined, ultracold fermionic strontium atoms, we observed density-dependent collisional frequency shifts. These collision effects were measured systematically and are supported by a theoretical description attributing them to inhomogeneities in the probe excitation process that render the atoms distinguishable. This work also yields insights for zeroing the clock density shift.
    Science 05/2009; 324(5925):360-3. · 31.20 Impact Factor
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    ABSTRACT: At ultracold temperatures, the Pauli exclusion principle suppresses collisions between identical fermions. This has been a strong motivation for the development of optical atomic clocks using fermionic isotopes. However, using a ^87Sr optical lattice clock we recently measured density-dependent frequency shifts of the clock transition. A systematic study of these collision effects has been completed and we have developed a theoretical model which provides a fundamental description of fermionic interactions including the effect of the measurement process on the dynamic evolution of the two particle correlation function. Importantly, for clock operations we have also identified experimental conditions that allow this density shift to be zeroed out.
    05/2009;
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    ABSTRACT: The uncertainty of our ^87Sr optical lattice clock operating on the ultranarrow ^1S0-^3P0 transition has recently reached 1.5x10-16. We will report our latest work in further reducing this uncertainty. One of the largest frequency shifts---a density shift---has now been characterized at the 5 x10-17 level. An understanding of the measurement-induced Fermionic interactions at ultracold temperatures has allowed us to zero the density shift altogether by operating the clock near a 50% excitation fraction. Furthermore, we report advancements in characterizing blackbody radiation-induced clock shifts. Recent progress toward high-fidelity manipulations of the long-lived nuclear- and electronic-spin states in alkaline earth atoms, a capability that will be useful for neutral-atom-based quantum information processing, will also be presented.
    05/2009;
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    ABSTRACT: Quantum state engineering of ultracold matter and precise control of optical fields have together allowed accurate measurement of light-matter interactions for applications in precision tests of fundamental physics. State-of-the-art lasers maintain optical phase coherence over one second. Optical frequency combs distribute this optical phase coherence across the entire visible and infrared parts of the electromagnetic spectrum, leading to the direct visualization and measurement of light ripples. At the same time, ultracold atoms confined in an optical lattice with zero differential ac Stark shift between two clock states allow us to minimize quantum decoherence while strengthening the clock signal. For 87Sr, we achieve a resonance quality factor > 2.4 × 1014 on the 1S0 - 3P0 doubly forbidden clock transition at 698 nm [1]. The uncertainty of this new clock has reached 1 × 10-16 and its instability approaches 1 × 10-15 at 1 s [2]. These developments represent a remarkable convergence of ultracold atoms, laser stabilization, and ultrafast science. Further improvements are still tantalizing, with quantum measurement and precision metrology combining forces to explore the next frontier.
    04/2009;
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    ABSTRACT: Modern capabilities in quantum state engineering of ultracold matter and precise control of light fields now permit accurate control of interactions between matter and field to suit applications for precision tests of fundamental physics. We report on our recent development of a highly stable and accurate optical atomic clock based on ultracold neutral Sr atoms confined in an optical lattice. We dis-cuss precision tools for the lattice clock, including stabilized lasers with sub-Hz linewidth, femtosecond-comb based technology allowing accurate clock comparison in both microwave and optical domains, and clock transfer over optical fibers. With microkelvin Sr atoms confined in an optical lattice that provide a zero differential a.c. Stark shift between two clock states, we achieve a resonance quality factor >2×10 14 on the 1 S0 − 3 P0 doubly forbidden 87 Sr clock transition at 698 nm. High resolution spectroscopy of spin-polarized atoms is used for both high-performance clock operations and accurate atomic structure measurement. The overall system-atic uncertainty of the clock has been evaluated at the 10 −16 level, while the stability approaches low 10 −15 at 1 s. These developments in precise engineering of light-atom interactions can be extended to the field of ultracold molecules, bringing new prospects for precision measurements, quantum control, and determinations of the constancy of the fundamental constants.
    01/2009;
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    ABSTRACT: Recent proposals have shown that a quantum degenerate gas of alkaline earth atoms can be used for a number of novel quantum computing and quantum simulation experiments. Strontium is a good candidate for such experiments because it can be controlled with high precision, as demonstrated in recent atomic clock experiments. Unfortunately, the small scattering length of strontium is not amenable to evaporative cooling techniques that are used to reach quantum degeneracy. Furthermore, increasing the scattering length of alkaline earths with a magnetic Feshbach resonance is not possible due to their spinless electronic ground state configuration. However, recent theoretical and experimental work suggests the possibility of changing scattering lengths in alkaline earths with laser light. Using this optical Feshbach resonance near strontium's narrow ^1S0->^3P1 intercombination transition might allow its scattering length to be controlled without significant atom loss. We report our recent progress in demonstrating an optical Feshbach resonance in strontium 88.
    01/2009;
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    ABSTRACT: We report on the improved characterization and operation of an optical frequency standard based on nuclear-spin-polarized, ultracold neutral strontium confined in a one dimensional optical lattice. We implement a remote optical carrier phase link between JILA and NIST Boulder Campus, permitting high precision evaluation of the Sr system with other optical standards. Frequency measurement against a free-space Ca standard enables determination of systematic shifts of the Sr standard at or below 1x10<sup>−16</sup> fractional uncertainty. We observe a density-dependent shift of the clock transition and its dependence on excited state fraction, with a zero crossing of the shift. We perform a 50-hour-long absolute frequency measurement of the strontium transition referenced to the NIST-F1 Cs fountain standard. This yields a value for the Sr clock transition frequency with a fractional uncertainty of 8.6x10<sup>−16</sup>, limited by the H-maser and Cs standards used. This represents our fifth, and the most accurate, measurement of the <sup>87</sup>Sr clock frequency.
    Frequency Control Symposium, 2008 IEEE International; 06/2008
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    ABSTRACT: We report on our recent progress on a optical atomic clock with high accuracy and stability based on ultracold fermionic lattice-confined ^87Sr atoms. We have evaluated the systematic effects at 1x10-16, enabling an improved measurement of the absolute clock transition frequency. The frequency of the ^1S0-^3P0 transition was measured as 429,28,04,29,73.83 ±0.37 Hz, where the final fractional uncertainty represents one of the most accurate measurements of an optical atomic frequency to date. In combination with data from the Paris and Tokyo groups, this measurement is used to limit Local Position Invariance by limiting coupling of fundamental constants to the gravitational potential.
    05/2008;
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    ABSTRACT: We have measured the ^87Sr ^1S0-^3P0 clock transition at nuSr = 429,28,04,29,73.83±0.37 Hz, limited by statistical uncertainty of the Sr/Cs comparison. Three international laboratories agree on the absolute frequency at the 1x10-15 (Boulder, Paris) to 4x10-15 (Boulder, Paris, Tokyo) level, making nuSr the best agreed-upon optical frequency to date. We analyze the global Sr frequency record to test Local Position Invariance by obtaining the best limits to date on coupling of fundamental constants to the ambient gravitational potential.
    05/2008;
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    ABSTRACT: The absolute frequency of the 1S0-3P0 clock transition of 87Sr has been measured to be 429 228 004 229 873.65 (37) Hz using lattice-confined atoms, where the fractional uncertainty of 8.6x10-16 represents one of the most accurate measurements of an atomic transition frequency to date. After a detailed study of systematic effects, which reduced the total systematic uncertainty of the Sr lattice clock to 1.5x10-16, the clock frequency is measured against a hydrogen maser which is simultaneously calibrated to the US primary frequency standard, the NIST Cs fountain clock, NIST-F1. The comparison is made possible using a femtosecond laser based optical frequency comb to phase coherently connect the optical and microwave spectral regions and by a 3.5 km fiber transfer scheme to compare the remotely located clock signals.
    Metrologia 04/2008; · 1.90 Impact Factor
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    ABSTRACT: The 1S0-3P0 clock transition frequency nuSr in neutral 87Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1 x 10(-15) level makes nuSr the best agreed-upon optical atomic frequency. We combine periodic variations in the 87Sr clock frequency with 199Hg+ and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant alpha, electron-proton mass ratio mu, and light quark mass. Furthermore, after 199Hg+, 171Yb+, and H, we add 87Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of alpha and mu.
    Physical Review Letters 04/2008; 100(14):140801. · 7.94 Impact Factor
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    ABSTRACT: Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies. Rigorous evaluations of these clocks require direct comparisons between them. We have realized a high-performance remote comparison of optical clocks over kilometer-scale urban distances, a key step for development, dissemination, and application of these optical standards. Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1 x 10(-16) fractional level, surpassing the current best evaluations of cesium (Cs) primary standards. We also report on the observation of density-dependent effects in the spin-polarized fermionic sample and discuss the current limiting effect of blackbody radiation-induced frequency shifts.
    Science 04/2008; 319(5871):1805-8. · 31.20 Impact Factor
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    ABSTRACT: We report on our recent evaluations of stability and accuracy of the JILA Sr optical lattice clock. We discuss precision tools for the lattice clock, including a stabilized clock laser with sub-Hz linewidth, fs-comb based technology allowing accurate clock comparison in both the microwave and optical domains, and clock transfer over optical fiber in an urban environment. High resolution spectroscopy (Q > 2 × 10 14) of lattice-confined, spin-polarized strontium atoms is used for both a high-performance optical clock and atomic structure measurement. Using a Ca optical standard for comparison, the overall systematic uncertainty of the Sr clock is reduced to < 2 × 10 -16 .
    04/2008;
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    ABSTRACT: Cooling and trapping of neutral atoms using laser techniques has enabled extensive progress in precise, coherent spectroscopy. In particular, trapping ultracold atoms in optical lattices in a tight confinement regime allows us to perform high-resolution spectroscopy unaffected by atomic motion. We report on the recent developments of optical lattice atomic clocks that have led to optical spectroscopy coherent at the one second timescale. The lattice clock techniques also open a promising pathway toward trapped ultracold molecules and the possible precision measurement opportunities such molecules offer.
    ChemPhysChem 03/2008; 9(3):375-82. · 3.35 Impact Factor
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    ABSTRACT: We describe the application of high accuracy Srspectroscopy to the measurement of the variation of thefundamental constants of nature. We first describe recent progressof the JILA Sr optical frequency standard, with a systematicuncertainty evaluation at the 10-16 fractional frequencylevel. Using recent internationally based measurements of the Srclock frequency, we show improved constraints of gravitational andtemporal changes in the fine structure constant and theelectron-proton mass ratio. Finally, we describe how ultracoldatomic strontium, confined in an optical lattice, can beassociated into molecular dimers and be used for amodel-independent measurement of the variation of theelectron-proton mass ratio.
    The European Physical Journal Special Topics 01/2008; 163(1):9-18. · 1.80 Impact Factor
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    ABSTRACT: Techniques of modern quantum optics allows for the preparation of atoms in well controlled quantum states ideal for precision measurements and tests of fundamental laws of physics. We report on our recent progress with a highly stable and accurate optical atomic clock based on ultracold fermionic 87Sr atoms confined in a one dimensional optical lattice. Currently, we have carried out a detailed evaluation of our clock at the 10-16 level and can report stability at 2 times 10-15 level at one second. At typical operating parameters for the clock we observe evidence of a density dependent clock shift. Operating the clock at a particular excitation ratio of ground state and excited clock state we observe a shift consistent with zero.
    01/2008;
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    ABSTRACT: Recent results from the JILA 87Sr optical lattice clock are presented. Using the tight confinement of an optical lattice in combination wit a sub-Hz linewidth diode laser we have achieved a pulse-length limited linewidth of 1.8 Hz for the 1S0- 3P0 clock transition. This corresponds to a quality factor of Q &ap; 2.4 x 1014, and is a record for coherent spectroscopy. With the addition of a small magnetic bias field, the high line Q of the clock transition has also allowed us to resolve the nuclear-spin sublevels, and make a precision measurement of the differential Landé g-factor between the 1S0 and 3P0. We present the current accuracy and stability of the lattice clock, and in addition, we report on our development of precision tools for the lattice clock, including a stabilized clock laser, fs-comb based technology allowing accurate clock comparison in both the microwave and optical domains, and clock transfer over an optical fiber in an urban environment.
    Proc SPIE 10/2007;
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    ABSTRACT: We have performed ultra-high resolution spectroscopy using a ^87Sr optical lattice clock. With the addition of a small magnetic bias field, the high line Q of the ^1S0-^3P0 clock transition has allowed us to resolve the nuclear-spin sublevels, and make a precision measurement of the differential Land'e g-factor between the ^1S0 and ^3P0 states arising from hyperfine mixing of the ^3P0 with the ^3P1 and ^1P1 states. Breaking the nuclear-spin degeneracy allows for a better characterization of systematic errors, and we have made measurements of these nuclear-spin related effects including the linear Zeeman shift and tensor polarizability. The ability to directly manipulate individual nuclear-spin levels also makes this an attractive system for quantum information. Recent progress towards an all optical comparison of atomic clocks, including the construction of a new strontium three-dimensional optical lattice will also be presented.
    06/2007;

Publication Stats

263 Citations
74 Downloads
908 Views
82.26 Total Impact Points

Institutions

  • 2008–2010
    • University of Colorado at Boulder
      • Department of Physics
      Boulder, CO, United States
    • Columbia University
      New York City, New York, United States
  • 2009
    • University of Colorado
      • Department of Physics
      Denver, Colorado, United States
  • 2008–2009
    • National Institute of Standards and Technology
      • Time and Frequency Division
      Gaithersburg, MD, United States