T. Loftus

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

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Publications (28)63.03 Total impact

  • R.J. Jones · T. Ido · T. Loftus · M. Boyd · A. Ludlow · K. Holman · M. Thorpe · K. Moll · J. Ye
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    ABSTRACT: We present results from several experiments in which the repetitive, coherent nature of stabilized mode-locked pulse trains are utilized. From absolute optical frequency measurements in ultracold Sr atoms to the coherent storage and amplification of optical pulse trains in high-finesse Fabry-Perot cavities, the stabilized femtosecond laser has become an indispensable tool in precision spectroscopy and ultrafast science.
    No preview · Article · Jul 2005 · Laser Physics
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    ABSTRACT: By varying the density of an ultracold Sr-88 sample from 10(9) to > 10(12) cm(-3), we make the first definitive measurement of the density-related frequency shift and linewidth broadening of the S-1(0)-P-3(1) optical clock transition in an alkaline earth system. In addition, we report the most accurate measurement to date of the Sr-88 S-1(0)-P-3(1) optical clock transition frequency. Including a detailed analysis of systematic errors, the frequency is [434 829 121 312 334 +/- 20(stat) +/- 33(syst)] Hz.
    Preview · Article · Apr 2005 · Physical Review Letters
  • T. Loftus · X.-Y. Xu · T. Ido · M. Boyd · J. L. Hall · A. Gallagher · J. Ye
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    ABSTRACT: We report the first experimental study of sub-Doppler cooling in alkaline earth atoms (87Sr) enabled by the presence of nuclear spin-originated magnetic degeneracy in the atomic ground state. A detailed investigation of system thermodynamics with respect to trapping beam parameters clearly reveals sub-Doppler temperatures despite the presence of multiple, closely spaced excited-states. This novel result is confirmed by a multi-level theory of the radiative cooling force. In addition, we describe an experimental study of magnetically trapped 3P2 state metastable 88Sr, a system that may ultimately provide unique insights into the physics of many-body systems with anisotropic interactions.
    No preview · Article · Dec 2004
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    Thomas H Loftus · Tetsuya Ido · Andrew D Ludlow · Martin M Boyd · Jun Ye
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    ABSTRACT: We present an extensive study of the unique thermal and mechanical dynamics for narrow-line cooling on the 1S0-3P1 88Sr transition. For negative detuning, trap dynamics reveal a transition from the semiclassical regime to the photon-recoil-dominated quantum regime, yielding an absolute minima in the equilibrium temperature below the single-photon-recoil limit. For positive detuning, the cloud divides into discrete momentum packets whose alignment mimics lattice points on a face-centered-cubic crystal. This novel behavior arises from velocity selection and "positive feedback" acceleration due to a finite number of photon recoils. Cooling is also achieved with blue-detuned light around a velocity where gravity balances the radiative force.
    Preview · Article · Sep 2004 · Physical Review Letters
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    Thomas H. Loftus · Tetsuya Ido · Martin M. Boyd · Andrew D. Ludlow · Jun Ye
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    ABSTRACT: Narrow line laser cooling is advancing the frontier for experiments ranging from studies of fundamental atomic physics to high precision optical frequency standards. In this paper, we present an extensive description of the systems and techniques necessary to realize 689 nm 1S0 - 3P1 narrow line cooling of atomic 88Sr. Narrow line cooling and trapping dynamics are also studied in detail. By controlling the relative size of the power broadened transition linewidth and the single-photon recoil frequency shift, we show that it is possible to continuously bridge the gap between semiclassical and quantum mechanical cooling. Novel semiclassical cooling process, some of which are intimately linked to gravity, are also explored. Moreover, for laser frequencies tuned above the atomic resonance, we demonstrate momentum-space crystals containing up to 26 well defined lattice points. Gravitationally assisted cooling is also achieved with blue-detuned light. Theoretically, we find the blue detuned dynamics are universal to Doppler limited systems. This paper offers the most comprehensive study of narrow line laser cooling to date. Comment: 14 pages, 19 figures
    Preview · Article · Jul 2004 · Physical Review A
  • T.H. Loftus · T. Ido · A. Ludlow · M. Boyd · Jun Ye
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    ABSTRACT: We present a detailed study of the thermodynamic and mechanical properties of a single photon recoil limited <sup>1</sup>S<sub>0</sub> - <sup>3</sup>P<sub>1</sub> <sup>88</sup>Sr magneto-optical trap for trapping laser frequencies both below and above the atomic resonance
    No preview · Conference Paper · Jun 2004
  • Tetsuya Ido · Thomas H. Loftus · Martin M. Boyd · Andrew D. Ludlow · Jun Ye
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    ABSTRACT: Distinctive thermal - mechanical dynamics for narrow line (^1S_0-^3P_1) - based ^88Sr cooling will be presented. The cooling transition natural linewidth (7.5 kHz) is only slightly larger than the single-photon recoil shift (4.7 kHz). Moreover, the radiative force is comparable to gravity. These properties give rise to distinctive thermodynamics. At large negative detunings, the balance between the trapping force and gravity leads to a self-adjusted trap position and a sample temperature independent of the actual laser detuning. For small laser detunings, thermodynamics similar to ordinary Doppler cooling including detuning-dependent minima appear, although with values globally smaller than Doppler theory predictions. At the lowest intensities, the trap temperature falls below the single photon recoil limit. Photon recoil-dominated cooling dynamics are further evidenced by suddenly switching the laser detuning from negative to positive values. Here, the atomic cloud divides into discrete momentum packets resembling lattice points on face-centered cubic crystals. This novel behavior arises from velocity selection and ``positive feedback'' acceleration due to a finite number of photon recoils. In this blue-detuned situation, atoms are even cooled around a velocity where the radiative force balances gravity.
    No preview · Article · May 2004
  • Xinye Xu · T.H. Loftus · A. Gallagher · J. Ye
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    ABSTRACT: A systematic study of the sub-Doppler cooling in a strontium magneto-optical trap is presented. A detailed theoretical analysis of this system, based on a fully expanded multi-level theory, is also discussed. Furthermore, density-related radiation heating dynamics are found to play a crucial role in this system with reduced sub-Doppler cooling force.
    No preview · Conference Paper · Jul 2003
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    ABSTRACT: We report the first experimental study of sub-Doppler cooling in alkaline earth atoms (87Sr) enabled by the presence of nuclear spin-originated magnetic degeneracy in the atomic ground state. Sub-Doppler cooling in a sigma(+)-sigma(-) configuration is achieved despite the presence of multiple, closely spaced excited states. This surprising result is confirmed by an expanded multilevel theory of the radiative cooling force. Detailed investigations of system performance have shed new insights into (sigma(+)-sigma(-)) cooling dynamics and will likely play an important role in the future development of neutral atom-based optical frequency standards.
    Full-text · Article · Jun 2003 · Physical Review Letters
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    ABSTRACT: We discuss theoretical investigations complementing the recently achieved laser cooling of a gas of ^87Sr atoms. (See also talk titled phSingle-stage sub-Doppler cooling of alkaline earth atoms.) The optical bloch equations are applied to a system with multiple excited states and the average cooling force on atoms is calculated for the sigma^+-sigma^- configuration. The behavior of this force as a function of velocity and the dependence on the energy splitting of the excited states are discussed.
    No preview · Article · May 2003
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    Xinye Xu · Thomas H. Loftus · John L. Hall · Alan Gallagher · Jun Ye
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    ABSTRACT: We present a detailed investigation of strontium magneto-optical trap (MOT) dynamics. Relevant physical quantities in the trap, such as temperature, atom number and density, and loss channels and lifetime, are explored with respect to various trap parameters. By studying the oscillatory response of a two-level 1S0–1P1 88Sr MOT, we firmly establish the laser cooling dynamics predicted by Doppler theory. Measurements of the MOT temperature, however, deviate severely from Doppler theory predictions, implying significant additional heating mechanisms. To explore the feasibility of attaining quantum degenerate alkaline-earth samples via evaporative cooling, we also present the first experimental demonstration of magnetically trapped metastable 88Sr. Furthermore, motivated by the goal of establishing the fermionic isotope 87Sr as one of the highest-quality, neutral-atom-based optical frequency standards, we present a preliminary study of sub-Doppler cooling in a 87Sr MOT. A dual-isotope (87Sr and 88Sr) MOT is also demonstrated.
    Full-text · Article · Apr 2003 · Journal of the Optical Society of America B
  • T. Loftus · J. R. Bochinski
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    ABSTRACT: Atomic ytterbium (Yb), magnesium (Mg), calcium (Ca), and strontium (Sr) possess a simple yet versatile internal level structure and a diversity of naturally abundant fermionic and bosonic isotopes, making these systems ideal for studies of cold collisions and weakly interacting quantum degenerate gases. Unlike alkali-metal atoms, however, Yb, Mg, Ca, and Sr cannot be magnetically trapped in the ground state. We analyze a solution to this problem involving magnetic trapping in a low-lying metastable excited state and predict that significant magnetic trap populations can be obtained via continuous, in situ loading from Yb and Sr 1S0-1P1 magneto-optical traps.
    No preview · Article · Jul 2002 · Physical Review A
  • Thomas Loftus · Xinye Xu · John Hall · Alan Gallagher · Jun Ye
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    ABSTRACT: Two-level-like ^88Sr atoms present an ideal platform for exploring magneto-optical trap (MOT) dynamics, enabling unique tests of semi-classical and quantum mechanical cooling mechanisms. We have measured the intensity, detuning and magnetic field dependence of the spring (kappa) and damping (alpha) coefficients for a ^1S0 ? ^1P1 ^88Sr MOT by monitoring center of mass trap oscillations induced by a weak, square-wave chopped push beam. Significantly, we find that single parameter fits to the observed behavior of kappa and alpha provide a unified and consistent picture of trap dynamics that agrees with Doppler based cooling theory at the level of 15%. Moreover, we find that the trapped atom temperature can be determined directly from the measured values for kappa and the trap size, with excellent agreement with results from conventional temperature measurement techniques. We do find, however, that the cloud temperature versus trapping beam intensity deviates significantly from the predictions of Doppler cooling theory. Our measurements represent the first detailed and conclusive studies of trapped two-level atom oscillation dynamics and provide and essential starting point for future studies of Sr atoms magnetically trapped in the ^3P2 metastable excited state.
    No preview · Article · Jul 2002
  • C. Regal · T. Loftus · M. Olsen · D. S. Jin
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    ABSTRACT: We have loaded an ultracold gas of fermionic atoms (^40K) into an optical dipole trap and isolated a mixture of the two spin states |F, mf > = |9/2, -9/2 > and |9/2, -7/2 >. With this mixture we have observed a magnetic-field Feshbach resonance that changes the elastic collision cross section by over three orders of magnitude^1. In addition we have measured a p-wave Feshbach resonance in collisions between the |9/2, -7/2 > atoms. We report on measurements of the inelastic loss at these resonances and discuss prospects for utilizing the s-wave resonance to study strong interactions in a quantum degenerate Fermi gas of atoms. ^1T. Loftus, C. A. Regal, C. Ticknor, J. L. Bohn, and D. S. Jin, cond-mat/0111571.
    No preview · Article · May 2002
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    T Loftus · CA Regal · C Ticknor · J L Bohn · D S Jin
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    ABSTRACT: We have loaded an ultracold gas of fermionic atoms into a far-off resonance optical dipole trap and precisely controlled the spin composition of the trapped gas. We have measured a magnetic-field Feshbach resonance between atoms in the two lowest energy spin states, /9/2,-9/2> and /9/2,-7/2>. The resonance peaks at a magnetic field of 201.5+/-1.4 G and has a width of 8.0+/-1.1 G. Using this resonance, we have changed the elastic collision cross section in the gas by nearly 3 orders of magnitude.
    Full-text · Article · May 2002 · Physical Review Letters
  • C Greiner · T Wang · T Loftus · T W Mossberg
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    ABSTRACT: We study the interaction of pulsed excitation fields with optically thin atomic ensembles subject to strong cavity-accelerated superradiance. In homogeneously broadened atom-field systems the excitation of superradiant instabilities is seen to lead to a quantization of the total pulse area accrued during excitation and subsequent superradiant decay. In inhomogeneously broadened systems, quasidiscretized area values and pulse area gaps (i.e., forbidden area values) are found. Predicted area discontinuities are demonstrated in cryogenically coherence-stabilized Tm(3+) ions.
    No preview · Article · Jan 2002 · Physical Review Letters
  • C. Greiner · B. Boggs · T. Wang · T. Loftus · T. W. Mossberg
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    ABSTRACT: Cavity-accelerated superradiance and pulse area quantization were discussed. The state of excitation created by an optical pulse in a resonant atomic system was measured. Results showed that the area quantization effect provides a powerful means to lock the cavity's output to specific areas.
    No preview · Article · Dec 2001 · Optics and Photonics News
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    ABSTRACT: Working with ytterbium (Yb), we demonstrate dual-isotope magneto-optic traps of extreme experimental simplicity yet containing either fermion-boson or boson-boson isotope pairs. Pairs studied include 171Yb+172Yb (a fermion-boson mixture) and 176Yb+174Yb and 174Yb+172Yb (boson-boson mixtures). Trapping is performed using the Yb (6s2)1S0-(6s6p)1P1 transition, an uncooled thermal source, and bichromatic trapping beams. Static and dynamic properties of the composite cloud are conveniently probed on the spin-forbidden (6s2)1S0-(6s6p)3P1 transition. A unique strategy for continuously loading these samples into magnetic traps is described.
    No preview · Article · Apr 2001 · Physical Review A
  • T. Loftus · J.R. Bochinski · T.W. Mossberg
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    ABSTRACT: Summary form only given. Studies of the classic problem of two non-degenerate atomic energy states exposed to an intense monochromatic driving field have enabled fundamental discoveries in quantum optics including inversionless optical gain, multiphoton laser action, and electromagnetically induced transparency. Nevertheless, the level degeneracy present in many atomic systems can and has been shown to play key roles in a variety of unique driven atom dynamics ranging from light-shift mediated stimulated Raman optical gain and lasing to electromagnetically induced absorption. To date, however, the potentially rich dynamics of these novel systems has received relatively little attention. Atomic barium (Ba) possesses a diversity of naturally abundant isotopes with varying degrees of level degeneracy, making it ideally suited to studies of degenerate two-level driven atom dynamics.
    No preview · Conference Paper · Feb 2001
  • T. Loftus · J.R. Bochinski · T.W. Mossberg
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    ABSTRACT: Summary form only given. Atomic ytterbium (Yb), magnesium (Mg), calcium (Ca), and strontium (Sr) possess simple internal level structure and a diversity of naturally abundant fermionic and bosonic isotopes, making these atoms ideal testing grounds for cold collision theories and future studies of weakly-interacting quantum degenerate gases. Lacking useful magnetic ground-state sub-structure, however, these atoms cannot be driven into the quantum degenerate regime by pursuing the only proven strategy, ground-state magnetic trapping followed by forced RF evaporation. We propose a novel solution to this problem that involves magnetic trapping in the low-lying <sup>3</sup>P<sub>2</sub> metastable excited state and demonstrate the possibility for deep magnetic traps using field gradients identical to those currently used for <sup>1</sup>S<sub>0</sub>-<sup>1</sup>P<sub>1</sub> Yb and alkaline-earth magneto-optical traps.
    No preview · Conference Paper · Feb 2001

Publication Stats

593 Citations
63.03 Total Impact Points

Institutions

  • 2002-2005
    • University of Colorado at Boulder
      • Department of Physics
      Boulder, Colorado, United States
  • 2004
    • University of Colorado
      • Department of Physics
      Denver, Colorado, United States
  • 1999-2002
    • University of Oregon
      • • Oregon Center for Optics
      • • Department of Physics
      Eugene, Oregon, United States