T. Loftus

National Institute of Standards and Technology, Gaithersburg, MD, United States

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Publications (27)65.19 Total impact

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    ABSTRACT: By varying the density of an ultracold 88Sr 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 1S0-3P1 optical clock transition in an alkaline earth system. In addition, we report the most accurate measurement to date of the 88Sr 1S0-3P1 optical clock transition frequency. Including a detailed analysis of systematic errors, the frequency is [434 829 121 312 334+/-20(stat)+/-33(syst)] Hz.
    Physical Review Letters 04/2005; 94(15):153001. · 7.73 Impact Factor
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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.
    12/2004;
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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.
    Physical Review Letters 09/2004; 93(7):073003. · 7.73 Impact Factor
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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
    Physical Review A 07/2004; · 3.04 Impact Factor
  • 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
    Quantum Electronics Conference, 2004. (IQEC). International; 06/2004
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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.
    05/2004;
  • 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.
    Quantum Electronics and Laser Science, 2003. QELS. Postconference Digest; 07/2003
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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.
    Physical Review Letters 06/2003; 90(19):193002. · 7.73 Impact Factor
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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.
    05/2003;
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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.
    Journal of the Optical Society of America B 04/2003; 20(5):968-976. · 2.21 Impact Factor
  • 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.
    Physical Review A 07/2002; 66(1). · 3.04 Impact Factor
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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.
    Physical Review Letters 05/2002; 88(17):173201. · 7.73 Impact Factor
  • 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.
    05/2002;
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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.
    Physical Review Letters 01/2002; 87(25):253602. · 7.73 Impact Factor
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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.
    Physical Review A 04/2001; 63(5). · 3.04 Impact Factor
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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.
    Quantum Electronics and Laser Science Conference, 2001. Technical Digest. Summaries of Papers Presented at the; 02/2001
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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.
    Quantum Electronics and Laser Science Conference, 2001. QELS '01. Technical Digest. Summaries of Papers Presented at the; 02/2001
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    ABSTRACT: We demonstrate that laser cooling, combined with V-scheme optical double-resonance spectroscopy, provides a sensitive means to measure isotope shifts and hyperfine splittings. Our technique is illustrated using the 398.8-nm (6s2)1S0-(6s6p)1P1 and 555.6-nm (6s2)1S0-(6s6p)3P1 transitions in a neutral ytterbium atomic beam having natural isotopic composition. With a precision comparable to existing approaches, our unique method has enabled the most complete single-technique survey to date of the 1S0-1P1 isotope shifts and hyperfine splittings.
    Physical Review A 01/2001; 63(2). · 3.04 Impact Factor
  • Optics and Photonics News 01/2001; 12(12).
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    ABSTRACT: We demonstrate a novel atomic-beam approach to obtaining isotope-specific driven-atom spectra using samples of arbitrary isotopic composition. The method employs modulation of target-isotope ground-state population by an up-stream preparation laser. Desired driven-atom signals generated downstream from the preparation laser are isolated using a lock-in amplifier referenced to the preparation-laser modulation frequency. In our experiments, an intensity-modulated laser resonant with the barium (6s^2) ^1S0 - (6s6p) ^3P1 791.1 nm intercombination transition selectively pumps ^138Ba atoms via radiative decays to the (6s5d) ^3D_1, 2 metastable states. Dressed-atom gain studies using the (6s^2) ^1S0 - (6s6p) ^1P1 553.5 nm transition demonstrate the efficacy of the method. We also explore this system under strong, bichromatic excitation and interpret the results utilizing doubly-dressed states. We note this technique has general utility for selectively isolating specific isotopic signals in systems possessing optically controllable atomic beam populations.
    05/2000;

Publication Stats

412 Citations
65.19 Total Impact Points

Institutions

  • 2002
    • National Institute of Standards and Technology
      • Quantum Physics Division
      Gaithersburg, MD, United States
  • 1999–2002
    • University of Oregon
      • • Department of Physics
      • • Oregon Center for Optics
      Eugene, OR, United States