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Westergaard PG, Thomsen JW, Henriksen MR, Michieletto M, Triches M, Lyngsø JK and Hald J (2016), "Compact, CO2-stabilized tuneable laser at 205 microns", Optics Express., feb, 2016. Vol. 24(5), pp. 4872. Optical Society of America.
Abstract: We demonstrate a compact fibre-based laser system at 2.05 microns stabilized to a CO2 transition using frequency modulation spectroscopy of a gas-filled hollow-core fibre. The laser exhibits an absolute frequency accuracy of 5 MHz, a frequency stability noise floor of better than 7 kHz or 5 × 10−11 and is tunable within ±200 MHz from the molecular resonance frequency while retaining roughly this stability and accuracy.
BibTeX:
@article{Westergaard2016,
  author = {Westergaard, Philip G. and Thomsen, Jan W. and Henriksen, Martin R. and Michieletto, Mattia and Triches, Marco and Lyngsø, Jens K. and Hald, Jan},
  title = {Compact, CO2-stabilized tuneable laser at 205 microns},
  journal = {Optics Express},
  publisher = {Optical Society of America},
  year = {2016},
  month = {feb},
  volume = {24},
  number = {5},
  pages = {4872},
  url = {https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-5-4872},
  doi = {10.1364/OE.24.004872}
}
Christensen BTR, Henriksen MR, Schäffer SA, Westergaard PG, Ye J, Holland MJ, Thomsen JW, Tieri D, Ye J, Holland MJ and Thomsen JW (2015), "Nonlinear Spectroscopy of Sr Atoms in an Optical Cavity for Laser Stabilization", Physical Review A., nov, 2015. Vol. 92(5), pp. 053820. American Physical Society.
BibTeX:
@article{Christensen2015,
  author = {Christensen, Bjarke T. R. and Henriksen, Martin Romme and Schäffer, Stefan Alaric and Westergaard, Philip G. and Ye, Jun and Holland, Murray J. and Thomsen, Jan W. and Tieri, David and Ye, Jun and Holland, Murray J. and Thomsen, Jan W.},
  title = {Nonlinear Spectroscopy of Sr Atoms in an Optical Cavity for Laser Stabilization},
  journal = {Physical Review A},
  publisher = {American Physical Society},
  year = {2015},
  month = {nov},
  volume = {92},
  number = {5},
  pages = {053820},
  url = {http://journals.aps.org/pra/abstract/10.1103/PhysRevA.92.053820},
  doi = {10.1103/PhysRevA.92.053820}
}
Christensen BTR, Schäffer SA, Henriksen MR, Westergaard PG, Ye J and Thomsen JW (2015), "Laser Stabilization on Velocity Dependent Nonlinear Dispersion of Sr Atoms in an Optical Cavity", In IEEE proceedings of IFCS-EFTF. IEEE.
Abstract: The development of simple and reliable high stability clock lasers is of great importance for future state-of-the-art optical clocks [1]-[5] and for future transportable optical clocks [6], [7]. Further development of clock lasers with better stability has so far been hindered by thermal noise in the reference cavity used for laser stabilization and conventional approaches for improvements may be technically challenging. It has been proposed [8]-[11] to improve the stability and reduce the complexity of state-of-the-art laser frequency stabilization by exploiting cavity QED systems consisting of atoms with a narrow optical transition coupled to a single mode of an optical cavity. The laser stabilization performance of a cavity QED system is affected by a number of system parameters such as the finite temperature of the atoms, the number of involved atoms and the laser power [12]-[14]. However, the dynamics of those elements have not yet been fully explored. Here we present a simple cavity QED system consisting of laser cooled strontium-88 atoms coupled to an optical cavity. We relate measurable quantities to the complex transmission coefficient which relates the input field to the output field. The optimal input power for stabilizing a laser to this system is experimentally determined and the optimal shot-noise-limited linewidth of the system is evaluated to 500 mHz. Furthermore, theoretical shot-noise-limited linewidths of similar cavity QED systems are evaluated for a number of different two electron systems.
BibTeX:
@inproceedings{ChristensenIFCS2015,
  author = {Christensen, Bjarke T. R. and Schäffer, Stefan Alaric and Henriksen, Martin Romme and Westergaard, Philip G. and Ye, Jun and Thomsen, Jan W.},
  title = {Laser Stabilization on Velocity Dependent Nonlinear Dispersion of Sr Atoms in an Optical Cavity},
  booktitle = {IEEE proceedings of IFCS-EFTF},
  publisher = {IEEE},
  year = {2015},
  url = {http://ieeexplore.ieee.org/xpls/absall.jsp?arnumber=7138858&tag=1},
  doi = {10.1109/FCS.2015.7138858}
}
Kjøller NK, Porsev SG, Westergaard PG, Andersen N and Thomsen JW (2015), "Hyperfine structure of the (3s3d) 3DJ manifold of 25Mg I", Physical Review A. Vol. 91(3)
Abstract: Based on spectroscopy of the (3s3p) 3P0-(3s3d) 3D1 Mg I transitions for the stable isotopes 24Mg(I =0), 25Mg (I = 5/2), and 26Mg (I = 0) we report measurements of the 25Mg (3s3d) 3DJ hyperfine coefficients A(3D1) = 141±7,A(3D2) =−59±6, and A(3D3) =−97±3 MHz. We find the hyperfine coefficients in agreement with state-of-the-art theoretical predictions presented here giving A(3D1) = 143.3±1.4,A(3D2) = −48.3±0.5, and A(3D3) =−96±1 MHz.We also reportmeasurements of the isotope shifts for the investigated transitions $Delta24–25 = 6±9 and $Delta24–26 = 59.7±0.5 MHz, significantly reducing the uncertainty compared to previous measurements.
BibTeX:
@article{Kjøller2015,
  author = {Kjøller, N. K. and Porsev, S. G. and Westergaard, P. G. and Andersen, N. and Thomsen, J. W.},
  title = {Hyperfine structure of the (3s3d) 3DJ manifold of 25Mg I},
  journal = {Physical Review A},
  year = {2015},
  volume = {91},
  number = {3},
  url = {http://journals.aps.org/pra/pdf/10.1103/PhysRevA.91.032515 http://link.aps.org/doi/10.1103/PhysRevA.91.032515},
  doi = {10.1103/PhysRevA.91.032515}
}
Nicholson TL, Blatt S, Bloom BJ, Williams JR, Thomsen JW, Ye J and Julienne PS (2015), "Optical Feshbach resonances: Field-dressed theory and comparison with experiments", Physical Review A., aug, 2015. Vol. 92(2), pp. 022709. American Physical Society.
BibTeX:
@article{Nicholson2015,
  author = {Nicholson, T. L. and Blatt, S. and Bloom, B. J. and Williams, J. R. and Thomsen, J. W. and Ye, J. and Julienne, Paul S.},
  title = {Optical Feshbach resonances: Field-dressed theory and comparison with experiments},
  journal = {Physical Review A},
  publisher = {American Physical Society},
  year = {2015},
  month = {aug},
  volume = {92},
  number = {2},
  pages = {022709},
  url = {http://journals.aps.org/pra/abstract/10.1103/PhysRevA.92.022709},
  doi = {10.1103/PhysRevA.92.022709}
}
Schäffer SA, Adsersen SS, Christensen BTR and Thomsen JW (2015), "Large Waist Cavity for Ultra-narrow Transition Spectroscopy", In IEEE proceedings of IFCS-EFTF. IEEE.
Abstract: Cavity enhanced spectroscopy on ultra-narrow transitions in atoms and molecules is a promising tool for frequency stabilization of clock lasers. However, the small beam waist of a typical cavity can effectively reduce the number of atoms in the system or introduce transit time broadening in the less controlled molecular systems. We present a cavity design with an internal telescope optimized to increase the waist from about 0:5 mm to 5 mm while still maintaining a convenient range of tuning parameters. Its usefulness in three separate spectroscopic systems is clarified.
BibTeX:
@inproceedings{Schaffer2015,
  author = {Schäffer, Stefan Alaric and Adsersen, Sigrid S and Christensen, Bjarke T R and Thomsen, Jan W},
  title = {Large Waist Cavity for Ultra-narrow Transition Spectroscopy},
  booktitle = {IEEE proceedings of IFCS-EFTF},
  publisher = {IEEE},
  year = {2015},
  url = {http://ieeexplore.ieee.org/xpls/absall.jsp?arnumber=7138923},
  doi = {0.1109/FCS.2015.7138923}
}
Tieri DA, Cooper J, Christensen BTR, Thomsen JW and Holland MJ (2015), "Laser stabilization using saturated absorption in a cavity-QED system", Physical Review A., jul, 2015. Vol. 92(1), pp. 013817. American Physical Society.
Abstract: We consider the phase stability of a local oscillator (or laser) locked to a cavity QED system comprised of atoms with an ultra-narrow optical transition. The atoms are cooled to millikelvin temperatures and then released into the optical cavity. Although the atomic motion introduces Doppler broadening, the standing wave nature of the cavity causes saturated absorption features to appear, which are much narrower than the Doppler width. These features can be used to achieve an extremely high degree of phase stabilization, competitive with the current state-of-the-art. Fur- thermore, the inhomogeneity introduced by finite atomic velocities can cause optical bistability to disappear, resulting in no regions of dynamic instability and thus enabling a new regime accessible to experiments where optimum stabilization may be achieved.
BibTeX:
@article{Tieri2015,
  author = {Tieri, D. A. and Cooper, J. and Christensen, Bjarke T. R. and Thomsen, J. W. and Holland, M. J.},
  title = {Laser stabilization using saturated absorption in a cavity-QED system},
  journal = {Physical Review A},
  publisher = {American Physical Society},
  year = {2015},
  month = {jul},
  volume = {92},
  number = {1},
  pages = {013817},
  url = {http://journals.aps.org/pra/abstract/10.1103/PhysRevA.92.013817},
  doi = {10.1103/PhysRevA.92.013817},
  eprint = {1506.08210}
}
Christensen BTR, Henriksen MR, Westergaard PG, Ye J and Thomsen JW (2014), "Prospects for frequency stabilization using collective effects of strontium atoms in an optical cavity", 2014 IEEE International Frequency Control Symposium (FCS)., may, 2014. , pp. 1-3. Ieee.
BibTeX:
@article{Christensen2014,
  author = {Christensen, Bjarke T. R. and Henriksen, Martin R. and Westergaard, Philip G. and Ye, Jun and Thomsen, Jan W.},
  title = {Prospects for frequency stabilization using collective effects of strontium atoms in an optical cavity},
  journal = {2014 IEEE International Frequency Control Symposium (FCS)},
  publisher = {Ieee},
  year = {2014},
  month = {may},
  pages = {1--3},
  url = {http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6859907},
  doi = {10.1109/FCS.2014.6859907}
}
Westergaard PGP, Christensen BTRB, Tieri D, Matin R, Cooper J, Holland M, Ye J and Thomsen JW (2014), "Observation of Motion-Dependent Nonlinear Dispersion with Narrow-Linewidth Atoms in an Optical Cavity", Physical Review Letters. Vol. 114(9), pp. 7.
Abstract: As an alternative to state-of-the-art laser frequency stabilisation using ultra-stable cavities, it has been proposed to exploit the non-linear effects from coupling of atoms with a narrow atomic transition to an optical cavity. Here we have constructed such a system and observed non-linear phase shifts of a narrow optical line by strong coupling of a sample of strontium-88 atoms to an optical cavity. The sample temperature of a few mK provides a domain where the Doppler energy scale is several orders of magnitude larger than the narrow linewidth of the optical transition. This makes the system sensitive to velocity dependent multi-photon scattering events (Dopplerons) that affect the cavity transmission significantly while leaving the phase signature relatively unaffected. By varying the number of atoms and the intra-cavity power we systematically study this non-linear phase signature which displays roughly the same features as for much lower temperature samples. This demonstration in a relatively simple system opens new possibilities not only for alternative routes to laser stabilization, but also for superradiant laser sources involving narrow line atoms.
BibTeX:
@article{Westergaard2015,
  author = {Westergaard, Philip G. Pg and Christensen, Bjarke T. R. Btr and Tieri, David and Matin, Rastin and Cooper, John and Holland, Murray and Ye, Jun and Thomsen, Jan W.},
  title = {Observation of Motion-Dependent Nonlinear Dispersion with Narrow-Linewidth Atoms in an Optical Cavity},
  journal = {Physical Review Letters},
  year = {2014},
  volume = {114},
  number = {9},
  pages = {7},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.114.093002},
  doi = {10.1103/PhysRevLett.114.093002},
  eprint = {1408.3983}
}
Blatt S, Nicholson TL, Bloom BJ, Williams JR, Thomsen JW, Julienne PS and Ye J (2011), "Measurement of Optical Feshbach Resonances in an Ideal Gas", Physical Review Letters., apr, 2011. Vol. 107(7), pp. 4.
Abstract: Using a narrow intercombination line in alkaline earth atoms to mitigate large inelastic losses, we explore the optical Feshbach resonance effect in an ultracold gas of bosonic 88Sr. A systematic measurement of three resonances allows precise determinations of the optical Feshbach resonance strength and scaling law, in agreement with coupled-channel theory. Resonant enhancement of the complex scattering length leads to thermalization mediated by elastic and inelastic collisions in an otherwise ideal gas. Optical Feshbach resonance could be used to control atomic interactions with high spatial and temporal resolution.
BibTeX:
@article{Blatt2011a,
  author = {Blatt, S. and Nicholson, T. L. and Bloom, B. J. and Williams, J. R. and Thomsen, J. W. and Julienne, P. S. and Ye, J.},
  title = {Measurement of Optical Feshbach Resonances in an Ideal Gas},
  journal = {Physical Review Letters},
  year = {2011},
  month = {apr},
  volume = {107},
  number = {7},
  pages = {4},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.107.073202 http://arxiv.org/abs/1104.0210},
  doi = {10.1103/PhysRevLett.107.073202},
  eprint = {1104.0210}
}
Jensen BB, Ming H, Westergaard PG, Gunnarsson K, Madsen MH, Brusch A, Hald J and Thomsen JW (2011), "Experimental Determination of the 24Mg I (3s3p) 3P2 Lifetime", Physical Review Letters., sep, 2011. Vol. 107(11), pp. 113001.
Abstract: We present the first experimental determination of the electric-dipole forbidden ð3s3pÞ3P2 !ð3s2Þ1S0 (M2) transition rate in 24Mg and compare to state-of-the-art theoretical predictions. Our measurement exploits a magnetic trap isolating the sample from perturbations and a magneto-optical trap as an amplifier converting each 3P2 !1S0 decay event into millions of photons readily detected. The transition rate is determined to be ð4:87?0:3Þ? 10?4 s?1 corresponding to a 3P2 lifetime of 2050þ140 ?110 sec. This value is in agreement with recent theoretical predictions, and to our knowledge the longest lifetime ever determined in a laboratory environment.
BibTeX:
@article{Jensen2011,
  author = {Jensen, B. B. and Ming, He and Westergaard, P. G. and Gunnarsson, K. and Madsen, M. H. and Brusch, A. and Hald, J. and Thomsen, J. W.},
  title = {Experimental Determination of the 24Mg I (3s3p) 3P2 Lifetime},
  journal = {Physical Review Letters},
  year = {2011},
  month = {sep},
  volume = {107},
  number = {11},
  pages = {113001},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.107.113001},
  doi = {10.1103/PhysRevLett.107.113001}
}
Martin MJ, Meiser D, Thomsen JW, Ye J and Holland MJ (2011), "Extreme nonlinear response of ultranarrow optical transitions in cavity QED for laser stabilization", Physical Review A., dec, 2011. Vol. 84(6), pp. 5.
Abstract: We explore the potential of direct spectroscopy of ultranarrowoptical transitions of atoms localized in an optical cavity. In contrast to stabilization against a reference cavity, which is the approach currently used for the most highly stabilized lasers, stabilization against an atomic transition does not suffer from Brownian thermal noise. Spectroscopy of ultranarrow optical transitions in a cavity operates in a very highly saturated regime in which nonlinear effects such as bistability play an important role. From the universal behavior of the Jaynes-Cummings model with dissipation, we derive the fundamental limits for laser stabilization using direct spectroscopy of ultranarrow atomic lines. We find that, with current lattice clock experiments, laser linewidths of about 1 mHz can be achieved in principle, and the ultimate limitations of this technique are at the 1 µHz level.
BibTeX:
@article{Martin2011,
  author = {Martin, M. J. and Meiser, D. and Thomsen, J. W. and Ye, Jun and Holland, M. J.},
  title = {Extreme nonlinear response of ultranarrow optical transitions in cavity QED for laser stabilization},
  journal = {Physical Review A},
  year = {2011},
  month = {dec},
  volume = {84},
  number = {6},
  pages = {5},
  url = {http://arxiv.org/abs/1105.2373 http://link.aps.org/doi/10.1103/PhysRevA.84.063813},
  doi = {10.1103/PhysRevA.84.063813},
  eprint = {1105.2373}
}
Steenstrup MP, Brusch A, Jensen BB, Hald J and Thomsen JW (2010), "Measurement of the (3s3p)1P–(3s3d)1D isotope shift in Mg i", Physical Review A., nov, 2010. Vol. 82(5), pp. 054501.
Abstract: We present measurements of the isotope shift for the (3s3p)1P–(3s3d)1D transitions at 881nm in Mg I. The three stable magnesium isotopes yielded a shift 24Mg–25Mg of (1342±20) MHz and 25Mg–26Mg of (1175±23) MHz. Measured shifts are consistent with recent relativistic many-body calculations of the mass effect.
BibTeX:
@article{Steenstrup2010,
  author = {Steenstrup, M. P. and Brusch, A. and Jensen, B. B. and Hald, J. and Thomsen, J. W.},
  title = {Measurement of the (3s3p)1P–(3s3d)1D isotope shift in Mg i},
  journal = {Physical Review A},
  year = {2010},
  month = {nov},
  volume = {82},
  number = {5},
  pages = {054501},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.82.054501},
  doi = {10.1103/PhysRevA.82.054501}
}
Swallows MD, Campbell GK, Ludlow AD, Boyd MM, Thomsen JW, Martin MJ, Blatt S, Nicholson TL and Ye J (2010), "Precision Measurement of Fermionic Collisions Using an 87 Sr Optical Lattice Clock", IEEE Transactions on ultrasonics, ferroelectrics and frequency control. Vol. 57(3), pp. 574-582.
Abstract: We describe recent progress on the JILA Sr opti- cal frequency standard, which has a systematic uncertainty at the 10−16 fractional frequency level. The dominant contribu- tions 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.
BibTeX:
@article{Swallows2010,
  author = {Swallows, Matthew D and Campbell, Gretchen K and Ludlow, Andrew D and Boyd, Martin M and Thomsen, Jan W and Martin, Michael J and Blatt, Sebastian and Nicholson, Travis L and Ye, Jun},
  title = {Precision Measurement of Fermionic Collisions Using an 87 Sr Optical Lattice Clock},
  journal = {IEEE Transactions on ultrasonics, ferroelectrics and frequency control},
  year = {2010},
  volume = {57},
  number = {3},
  pages = {574--582},
  url = {http://ieeexplore.ieee.org/xpls/absall.jsp?arnumber=5422497},
  doi = {10.1109/TUFFC.2010.1449}
}
Blatt S, Thomsen J, Campbell G, Ludlow A, Swallows M, Martin M, Boyd M and Ye J (2009), "Rabi spectroscopy and excitation inhomogeneity in a one-dimensional optical lattice clock", Physical Review A., nov, 2009. Vol. 80(5), pp. 052703.
Abstract: We investigate the influence of atomic motion on precision Rabi spectroscopy of ultracold fermionic atoms confined in a deep one-dimensional optical lattice. We analyze the spectral components of longitudinal side- band 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 line shapes 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.
BibTeX:
@article{Blatt2009a,
  author = {Blatt, S. and Thomsen, J. and Campbell, G. and Ludlow, A. and Swallows, M. and Martin, M. and Boyd, M. and Ye, J.},
  title = {Rabi spectroscopy and excitation inhomogeneity in a one-dimensional optical lattice clock},
  journal = {Physical Review A},
  year = {2009},
  month = {nov},
  volume = {80},
  number = {5},
  pages = {052703},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.80.052703},
  doi = {10.1103/PhysRevA.80.052703}
}
Campbell GK, Boyd MM, Thomsen JW, Martin MJ, Blatt S, Swallows MD, Nicholson TL, Fortier T, Oates CW, Diddams SA, Lemke ND, Naidon P, Julienne P, Ye J and Ludlow AD (2009), "REPORTS Probing Interactions Between Ultracold Fermions", Science. Vol. 324(April), pp. 360-363.
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.
BibTeX:
@article{Campbell2009,
  author = {Campbell, G K and Boyd, M M and Thomsen, J W and Martin, M J and Blatt, S and Swallows, M D and Nicholson, T L and Fortier, T and Oates, C W and Diddams, S A and Lemke, N D and Naidon, P and Julienne, P and Ye, Jun and Ludlow, A D},
  title = {REPORTS Probing Interactions Between Ultracold Fermions},
  journal = {Science},
  year = {2009},
  volume = {324},
  number = {April},
  pages = {360--363},
  url = {https://www.sciencemag.org/content/324/5925/360.full.pdf},
  doi = {10.1126/science.1169724}
}
He M, Therkildsen K, Jensen B, Brusch A, Thomsen J and Porsev S (2009), "Isotope shifts of the (3s3p) 3P0,1,2-(3s4s) 3S1 Mg I transitions", Physical Review A., aug, 2009. Vol. 80(2), pp. 024501.
Abstract: We report measurements of the isotope shifts of the ?3s3p? 3P0,1,2-?3s4s? 3S1 Mg I transitions for the stable isotopes 24Mg ?I=0?, 25Mg ?I=5/2?, and 26Mg ?I=0?. Furthermore, the 25Mg 3S1 hyperfine coefficient A?3S1?=?−321.6?1.5? MHz is extracted and found to be in excellent agreement with state-of-the-art theoret- ical predictions giving A?3S1?=−325 MHz and B?3S1??10−5 MHz. Compared to previous measurements, the data presented in this work are improved up to a factor of 10.
BibTeX:
@article{He2009,
  author = {He, Ming and Therkildsen, Kasper and Jensen, Brian and Brusch, Anders and Thomsen, Jan and Porsev, Sergey},
  title = {Isotope shifts of the (3s3p) 3P0,1,2-(3s4s) 3S1 Mg I transitions},
  journal = {Physical Review A},
  year = {2009},
  month = {aug},
  volume = {80},
  number = {2},
  pages = {024501},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.80.024501},
  doi = {10.1103/PhysRevA.80.024501}
}
He M, Jensen BB, Therkildsen KT, Brusch A and Thomsen JW (2009), "Metastable Magnesium fluorescence spectroscopy using a frequency-stabilized 517 nm laser", Optics Express., apr, 2009. Vol. 17(9), pp. 7682.
Abstract: We present a laser operating at 517 nm for our Magnesium laser- cooling and atomic clock project. A two-stage Yb-doped fiber amplifier (YDFA) system generates more than 1.5 W of 1034 nm light when seeded with a 15 mW diode laser. Using a periodically poled lithium niobate (PPLN) waveguide, we obtained more than 40 mW of 517 nm output power by single pass frequency doubling. In addition, fluorescence spectroscopy of metastable magnesium atoms could be used to stabilize the 517 nm laser to an absolute frequency within 1 MHz.
BibTeX:
@article{He2009a,
  author = {He, Ming and Jensen, Brian B. and Therkildsen, Kasper T. and Brusch, Anders and Thomsen, Jan W.},
  title = {Metastable Magnesium fluorescence spectroscopy using a frequency-stabilized 517 nm laser},
  journal = {Optics Express},
  year = {2009},
  month = {apr},
  volume = {17},
  number = {9},
  pages = {7682},
  url = {http://www.opticsinfobase.org/abstract.cfm?URI=oe-17-9-7682},
  doi = {10.1364/OE.17.007682}
}
Ludlow AD, Campbell GK, Blatt S, Boyd MM, Martin MJ, Nicholson TL, Swallows M, Thomsen JW, Fortier T, Oates CW, Diddams Sa, Lemke ND, Barber Z, Porsev SG and Ye J (2009), "Quantum Metrology With Lattice-Confined Ultracold Sr Atoms", Frequency Standards and Metrology - Proceedings of the 7th Symposium. Singapore , pp. 73-81. World Scientific Publishing Co. Pte. Ltd..
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 87 Sr, we achieve a resonance quality factor >2.4 x 1014 on the 1 S0 – 3 P0 doubly forbidden clock transition at 698 nm [1]. The uncertainty of this new clock has reached 1 x 10-16 and its instability approaches 1 x 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.
BibTeX:
@article{Ludlow2009,
  author = {Ludlow, A. D. and Campbell, G. K. and Blatt, S. and Boyd, M. M. and Martin, M. J. and Nicholson, T. L. and Swallows, M. and Thomsen, J. W. and Fortier, T. and Oates, C. W. and Diddams, S. a. and Lemke, N. D. and Barber, Z. and Porsev, S. G. and Ye, Jun},
  title = {Quantum Metrology With Lattice-Confined Ultracold Sr Atoms},
  journal = {Frequency Standards and Metrology - Proceedings of the 7th Symposium},
  publisher = {World Scientific Publishing Co. Pte. Ltd.},
  year = {2009},
  pages = {73--81},
  url = {http://eproceedings.worldscinet.com/9789812838223/97898128382230007.html},
  doi = {10.1142/9789812838223{\_}0007}
}
Blatt S, Ludlow A, Campbell G, Thomsen J, Zelevinsky T, Boyd M, Ye J, Baillard X, Fouché M, Le Targat R, Brusch A, Lemonde P, Takamoto M, Hong F-L, Katori H and Flambaum V (2008), "New Limits on Coupling of Fundamental Constants to Gravity Using Sr87 Optical Lattice Clocks", Physical Review Letters., apr, 2008. Vol. 100(14), pp. 140801.
Abstract: The 1S0-3P0 clock transition frequency ?Sr 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?10?15 level makes ?Sr 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 ?, electron-proton mass ratio ?, 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 ? and ?.
BibTeX:
@article{Blatt2008,
  author = {Blatt, S. and Ludlow, A. and Campbell, G. and Thomsen, J. and Zelevinsky, T. and Boyd, M. and Ye, J. and Baillard, X. and Fouché, M. and Le Targat, R. and Brusch, A. and Lemonde, P. and Takamoto, M. and Hong, F.-L. and Katori, H. and Flambaum, V.},
  title = {New Limits on Coupling of Fundamental Constants to Gravity Using Sr87 Optical Lattice Clocks},
  journal = {Physical Review Letters},
  year = {2008},
  month = {apr},
  volume = {100},
  number = {14},
  pages = {140801},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.100.140801},
  doi = {10.1103/PhysRevLett.100.140801}
}
Campbell GK, Ludlow AD, Blatt S, Thomsen JW, Martin MJ, de Miranda MHG, Zelevinsky T, Boyd MM, Ye J, Diddams Sa, Heavner TP, Parker TE and Jefferts SR (2008), "The absolute frequency of the 87 Sr optical clock transition", Metrologia., apr, 2008. Vol. 45(5), pp. 539-548.
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.
BibTeX:
@article{Campbell2008,
  author = {Campbell, Gretchen K. and Ludlow, Andrew D. and Blatt, Sebastian and Thomsen, Jan W. and Martin, Michael J. and de Miranda, Marcio H. G. and Zelevinsky, Tanya and Boyd, Martin M. and Ye, Jun and Diddams, Scott a. and Heavner, Thomas P. and Parker, Thomas E. and Jefferts, Steven R.},
  title = {The absolute frequency of the 87 Sr optical clock transition},
  journal = {Metrologia},
  year = {2008},
  month = {apr},
  volume = {45},
  number = {5},
  pages = {539--548},
  url = {http://arxiv.org/abs/0804.4509 http://stacks.iop.org/0026-1394/45/i=5/a=008?key=crossref.617fc9cd2168c86cf4fccd72eac5e09c},
  doi = {10.1088/0026-1394/45/5/008},
  eprint = {0804.4509}
}
Hansen P, Therkildsen K, Malossi N, Jensen B, van Ooijen E, Brusch A, Müller J, Hald J and Thomsen J (2008), "Measurement of the 3s3p 3P1 lifetime in magnesium using a magneto-optical trap", Physical Review A., jun, 2008. Vol. 77(6), pp. 062502.
Abstract: We demonstrate an accurate method for measuring the lifetime of long-lived metastable magnetic states using a magneto-optical trap ?MOT?. Through optical pumping, the metastable ?3s3p? 3P1 level is populated in a standard MOT. During the optical pumping process, a fraction of the population is captured in the magnetic quadrupole field of the MOT. When the metastable atoms decay to the ?3s2? 1S0 ground state they are recap- tured into the MOT. In this system no alternative cascading transition is possible. The lifetime of the metastable level is measured directly as an exponential load time of the MOT.We have experimentally tested our method by measuring the lifetime of the ?3s3p? 3P1 of 24Mg. This lifetime has been measured numerous times previously, but with quite different results. Using our method we find the ?3s3p? 3P1 lifetime to be ?4.4?0.2? ms. Theoretical values point toward a lower value for the lifetime.
BibTeX:
@article{Hansen2008,
  author = {Hansen, P. and Therkildsen, K. and Malossi, N. and Jensen, B. and van Ooijen, E. and Brusch, A. and Müller, J. and Hald, J. and Thomsen, J.},
  title = {Measurement of the 3s3p 3P1 lifetime in magnesium using a magneto-optical trap},
  journal = {Physical Review A},
  year = {2008},
  month = {jun},
  volume = {77},
  number = {6},
  pages = {062502},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.77.062502},
  doi = {10.1103/PhysRevA.77.062502}
}
Olausson CB, Falk CI, Lyngsø KJ, Jensen BB, Therkildsen KT, Thomsen JW, Hansen KP, Bjarklev A and Broeng J (2008), "Amplification and ASE suppression in a solid photonic bandgap fibre", Optics Express. Vol. 16(18), pp. 13657-13662.
Abstract: We demonstrate suppression of amplified spontaneous emission at the conventional ytterbium gain wavelengths around 1030 nm in a cladding-pumped polarization-maintaining ytterbium-doped all-solid photonic crystal fibre. The fibre works through combined index and bandgap guiding. Furthermore, we show that the peak of the amplified spontaneous emission can be shifted towards longer wavelengths by rescaling the fibre dimensions. Thereby one can obtain lasing or amplification at longer wavelengths (1100 nm – 1200 nm) as the amount of amplification in the fibre is shown to scale with the power of the amplified spontaneous emission.
BibTeX:
@article{Hansen2008a,
  author = {Olausson, C. B. and Falk, C. I. and Lyngsø, K. J. and Jensen, B. B. and Therkildsen, K. T. and Thomsen, J. W. and Hansen, K P and Bjarklev, A and Broeng, J},
  title = {Amplification and ASE suppression in a solid photonic bandgap fibre},
  journal = {Optics Express},
  year = {2008},
  volume = {16},
  number = {18},
  pages = {13657--13662},
  url = {https://www.osapublishing.org/oe/abstract.cfm?&uri=oe-16-18-13657},
  doi = {10.1364/OE.16.013657}
}
Ludlow aD, Zelevinsky T, Campbell GK, Blatt S, Boyd MM, de Miranda MHG, Martin MJ, Thomsen JW, Foreman SM, Ye J, Fortier TM, Stalnaker JE, Diddams SA, Le Coq Y, Barber ZW, Poli N, Lemke ND, Beck KM, Oates CW, Miranda MHGD, Martin MJ, Thomsen JW, Stalnaker JE, Diddams SA, Coq YL, Barber ZW, Poli N, Beck KM and Oates CW (2008), "Sr lattice clock at 1 x 10(-16) fractional uncertainty by remote optical evaluation with a Ca clock.", Science (New York, N.Y.)., mar, 2008. Vol. 319(5871), pp. 1805-8.
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.
BibTeX:
@article{Ludlow2008,
  author = {Ludlow, a D and Zelevinsky, T and Campbell, G K and Blatt, S and Boyd, M M and de Miranda, M H G and Martin, M J and Thomsen, J W and Foreman, S M and Ye, Jun and Fortier, T M and Stalnaker, J E and Diddams, S A and Le Coq, Y and Barber, Z W and Poli, N and Lemke, N D and Beck, K M and Oates, C W and Miranda, M H G De and Martin, M J and Thomsen, J W and Stalnaker, J E and Diddams, S A and Coq, Y Le and Barber, Z W and Poli, N and Beck, K M and Oates, C W},
  title = {Sr lattice clock at 1 x 10(-16) fractional uncertainty by remote optical evaluation with a Ca clock.},
  journal = {Science (New York, N.Y.)},
  year = {2008},
  month = {mar},
  volume = {319},
  number = {5871},
  pages = {1805--8},
  url = {www.sciencemag.org/cgi/content/full/1153341/DC1 http://www.ncbi.nlm.nih.gov/pubmed/18276849},
  doi = {10.1126/science.1153341}
}
Ludlow AD, Blatt S, Zelevinsky T, Campbell GK, Martin MJ, Thomsen JW, Boyd MM and Ye J (2008), "Ultracold strontium clock: Applications to the measurement of fundamental constant variations", The European Physical Journal Special Topics., nov, 2008. Vol. 163(1), pp. 9-18.
Abstract: We describe the application of high accuracy Sr spectroscopy to the measurement of the variation of the fundamental constants of nature. We first describe recent progress of the JILA Sr optical frequency standard, with a system- atic uncertainty evaluation at the 10−16 fractional frequency level. Using recent internationally based measurements of the Sr clock frequency, we show improved constraints of gravitational and temporal changes in the fine structure constant and the electron-proton mass ratio. Finally, we describe how ultracold atomic strontium, confined in an optical lattice, can be associated into molecular dimers and be used for a model-independent measurement of the variation of the electron- proton mass ratio.
BibTeX:
@article{Ludlow2008a,
  author = {Ludlow, A. D. and Blatt, S. and Zelevinsky, T. and Campbell, G. K. and Martin, M. J. and Thomsen, J. W. and Boyd, M. M. and Ye, J.},
  title = {Ultracold strontium clock: Applications to the measurement of fundamental constant variations},
  journal = {The European Physical Journal Special Topics},
  year = {2008},
  month = {nov},
  volume = {163},
  number = {1},
  pages = {9--18},
  url = {http://www.springerlink.com/index/10.1140/epjst/e2008-00806-8},
  doi = {10.1140/epjst/e2008-00806-8}
}
Ludlow AD, Campbell GK, Blatt S, Boyd MM, Zelevinsky T, Martin MJ, de Miranda MHG, Tomsen JW and Ye J (2008), "Strontium Optical Lattice Clock : 10 -16 Uncertainty", IEEE. , pp. 449-450.
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 1x10-16 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 8.6x10-16, limited by the H-maser and Cs standards used. This represents our fifth, and the most accurate, measurement of the 87Sr clock frequency. I.
BibTeX:
@article{Martin2008,
  author = {Ludlow, A D and Campbell, G K and Blatt, S and Boyd, M M and Zelevinsky, T and Martin, M J and de Miranda, M H G and Tomsen, J W and Ye, Jun},
  title = {Strontium Optical Lattice Clock : 10 -16 Uncertainty},
  journal = {IEEE},
  year = {2008},
  pages = {449--450}
}
Nicolin AI, Jensen MH, Thomsen JW and Carretero-González R (2008), "Resonant energy transfer in Bose–Einstein condensates", Physica D: Nonlinear Phenomena., oct, 2008. Vol. 237(19), pp. 2476-2481.
Abstract: We consider the dynamics of a dilute, magnetically-trapped one-dimensional Bose–Einstein condensate whose scattering length is periodically modulated with a frequency that linearly increases in time. We show that the response frequency of the condensate locks to its eigenfrequency for appropriate ranges of the parameters. The locking sets in at resonance, i.e., when the effective frequency of driving field is equal to the eigenfrequency, and is accompanied by a sudden increase of the oscillations amplitude due to resonant energy transfer.We show that the dynamics of the condensate is given, to leading order, by a driven harmonic oscillator on the time-dependent part of the width of the condensate. This equation captures accurately both the locking and the resonant energy transfer as it is evidenced by comparison with direct numerical simulations of original Gross–Pitaevskii equation.
BibTeX:
@article{Nicolin2008,
  author = {Nicolin, Alexandru I. and Jensen, Mogens H. and Thomsen, Jan W. and Carretero-González, R.},
  title = {Resonant energy transfer in Bose–Einstein condensates},
  journal = {Physica D: Nonlinear Phenomena},
  year = {2008},
  month = {oct},
  volume = {237},
  number = {19},
  pages = {2476--2481},
  url = {http://linkinghub.elsevier.com/retrieve/pii/S0167278908000894},
  doi = {10.1016/j.physd.2008.03.004}
}
Nielsen CV, Lyngsø JK, Thorseth A, Galouzis M, Therkildsen KT, van Ooijen ED and Thomsen JW (2008), "Characterization of a magnetic trap by polarization dependent Zeeman spectroscopy", The European Physical Journal D., apr, 2008. Vol. 48(1), pp. 111-119.
Abstract: This paper demonstrates a detailed experimental study of our cloverleaf magnetic trap for sodium atoms. By using polarization dependent Zeeman spectroscopy of our atomic beam, passing the magnetic trap region, we have determined important trap parameters such as gradients, their curvatures and corresponding trap frequencies. Experimental findings are compared to theoretical calculations as well as complementary methods of characterizing the trap.
BibTeX:
@article{Nielsen2008,
  author = {Nielsen, C. V. and Lyngsø, J. K. and Thorseth, A. and Galouzis, M. and Therkildsen, K. T. and van Ooijen, E. D. and Thomsen, J. W.},
  title = {Characterization of a magnetic trap by polarization dependent Zeeman spectroscopy},
  journal = {The European Physical Journal D},
  year = {2008},
  month = {apr},
  volume = {48},
  number = {1},
  pages = {111--119},
  url = {http://www.springerlink.com/index/10.1140/epjd/e2008-00068-4},
  doi = {10.1140/epjd/e2008-00068-4}
}
Therkildsen KT, Jensen BB, Ryder CP, Malossi N and Thomsen JW (2008), "Measurement of the Spin-forbidden Decay rate (3s3d) 1D2 to (3s3p) 3P2,1 in 24Mg", Physical Review A., mar, 2008. Vol. 79(3), pp. 034501.
Abstract: We have measured the spin-forbidden decay rate from (3s3d)1D2 \$ (3s3p)3P2,1 in 24Mg atoms trapped in a magneto-optical trap. The total decay rate, summing up both exit channels (3s3p)3P1 and (3s3p)3P2, yields (196 \$ 10) s-1 in excellent agreement with resent relativistic many-body calculations of [S.G. Porsev et al., Phys. Rev. A. $textbf64, 012508 (2001)]. The characterization of this decay channel is important as it may limit the performance of quantum optics experiments carried out with this ladder system as well as two-photon cooling experiments currently explored in several groups.
BibTeX:
@article{Therkildsen2008,
  author = {Therkildsen, K. T. and Jensen, B. B. and Ryder, C. P. and Malossi, N. and Thomsen, J. W.},
  title = {Measurement of the Spin-forbidden Decay rate (3s3d) 1D2 to (3s3p) 3P2,1 in 24Mg},
  journal = {Physical Review A},
  year = {2008},
  month = {mar},
  volume = {79},
  number = {3},
  pages = {034501},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.79.034501 http://arxiv.org/abs/0812.3800},
  doi = {10.1103/PhysRevA.79.034501},
  eprint = {0812.3800}
}
Thomsen JW, Campbell GK, Ludlow aD, Blatt S, Martin MJ, Zelevinsky T, Zanon-Willette T and Boyd MM (2008), "Strontium optical lattice clock with high accuracy and stability", 2008 Conference on Precision Electromagnetic Measurements Digest., jun, 2008. , pp. 90-91. Ieee.
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 x 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.
BibTeX:
@article{Thomsen2008,
  author = {Thomsen, J. W. and Campbell, G. K. and Ludlow, a. D. and Blatt, S. and Martin, M. J. and Zelevinsky, T. and Zanon-Willette, T. and Boyd, M. M.},
  title = {Strontium optical lattice clock with high accuracy and stability},
  journal = {2008 Conference on Precision Electromagnetic Measurements Digest},
  publisher = {Ieee},
  year = {2008},
  month = {jun},
  pages = {90--91},
  url = {http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=4574667},
  doi = {10.1109/CPEM.2008.4574667},
  eprint = {arXiv:0801.1874}
}
Dunn J, Thomsen J, Greene C and Cruz F (2007), "Coherent quantum engineering of free-space laser cooling", Physical Review A., jul, 2007. Vol. 76(1), pp. 011401.
Abstract: Two distinct lasers are shown to permit controlled cooling of a three-level atomic system to a regime particularly useful for group-II atoms. Alkaline-earth-metal atoms are difficult to laser cool to the micro- or nanokelvin regime, but this technique exhibits encouraging potential to circumvent current roadblocks. Intro- duction of a sparse-matrix technique permits efficient solution of the master equation for the stationary density matrix, including the quantized atomic momentum. This overcomes long-standing inefficiencies of exact so- lution methods, and it sidesteps inaccuracies of frequently implemented semiclassical approximations. The realistic theoretical limiting temperatures are optimized over the full parameter space of detunings and inten- sities. A qualitative interpretation based on the phenomenon of electromagnetically induced transparency re- veals dynamical effects due to photon-atom dressing interactions that generate non-Lorentzian line shapes. Through coherent engineering of an asymmetric Fano-type profile, the temperature can be lowered down to the recoil limit range.
BibTeX:
@article{Dunn2007,
  author = {Dunn, Josh and Thomsen, J. and Greene, Chris and Cruz, Flavio},
  title = {Coherent quantum engineering of free-space laser cooling},
  journal = {Physical Review A},
  year = {2007},
  month = {jul},
  volume = {76},
  number = {1},
  pages = {011401},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.76.011401},
  doi = {10.1103/PhysRevA.76.011401}
}
van der Stam KMR, Meppelink R, Vogels JM, Thomsen JW and van der Straten P (2007), "Resonant superradiant backward-scattering as a source for many-particle entanglement", jul, 2007. , pp. 5.
Abstract: We investigate the atom pair production by superradiant backward-scattering from a Bose-Einstein condensate. By driving the superradiant process with two frequencies we can extend both the range of pulse duration and intensity by two orders of magnitude and obtain full control over the number of scattered atoms in forward and backward direction. We show that the atoms scattered in forward direction are strongly correlated with the atoms scattered in backward direction, which makes resonant superradiant backward-scattering a promising candidate for many-particle entanglement.
BibTeX:
@article{VanderStam2007,
  author = {van der Stam, K. M. R. and Meppelink, R. and Vogels, J. M. and Thomsen, J. W. and van der Straten, P.},
  title = {Resonant superradiant backward-scattering as a source for many-particle entanglement},
  year = {2007},
  month = {jul},
  pages = {5},
  url = {http://arxiv.org/abs/0707.1465},
  eprint = {0707.1465}
}