Lifetime Measurements and Absolute Oscillator Strengths for Single Ionized Thorium (ThII)

H. Simonsen, T. Worm, P. Jessen, and O. Poulen

Institute of Physics, University of Aarhus, DK-8000 Aarhus C, Denmark
 

Using collinear fast beam cw dye laser modulation spectroscopy accurate lifetimes in ThII have been measured. Together with known branching ratios these lifetimes have allowed the determination of absolute oscillator strengths for ThII. This element is of astrophysical interest as a chronometer for stellar and galaxy evolution, with oscillator strengths playing an important role in synthesis of stellar spectral data.
 

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Laser Modification of Ultracold Collisions: Experiment

P. D. Lett

Electron and Optical Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
 

P. S. Jessen, W. D. Phillips, S. L. Rolston, C. I. Westbrook and P. L. Gould

Atomic Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
 

Julienne recently predicted a dramatic laser-intensity-dependent modification of the associative ionization (AI) rate in ultracold collisions. We observe such a modification, but with a behavior inconsistent with the originally proposed mechanism. Furthermore, we find resonant structure in the spectrum of AI rate versus laser frequency, showing the importance of molecular bound states in the AI process. These observations are explained in a new theoretical treatment by Julienne and Heather (preceding Letter).
 

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Laser cooling of stored ions in ASTRID : a storage ring for ions and electrons

J. S. Hangst,¹ K. Berg-Sørensen, P. S. Jessen, M. Kristensen, K. Mølmer, J. S. Nielsen, O. Poulsen, J. P. Schiffer² and P. Shi

1. Institute of Physics and Astronomy, University of Aarhus, DK-8000 Århus, C Denmark
2. Søren Pape Møller Institute for Synchrotron Radiation, University of Aarhus, DK-8000 Århus, C Denmark
 

A small storage ring, ASTRID, for ions and electrons has been constructed. It is a dual-purpose machine, serving as a storage ring for either ions or electrons for synchrotron-radiation production. The ring has for more than one year been operational with ions and has recently been commissioned for electron storage. Both these running modes will be described as well as results given from the first experiments with laser cooled ions. Finally, prospectsfor experimentswith superhigh mass and isotope selectivity will be discussed.
 

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Observation of Quantized Motion of Rb Atoms in an Optical Field

P. S. Jessen, C. Gerz, P. D. Lett, W. D. Phillips, S. L. Rolston, R. J. C. Spreeuw and C. I. Westbrook

National Institute of Standards and Technology, U.S. Department of Commerce,
Technology Administration, PHYS A167, Gaithersburg, Maryland 20899
 

We observe transitions of laser-cooled Rb between vibrational levels in subwavelength-sized optical potential wells, using high-resolution spectroscopy of resonance fluorescence. We measure the spacing of the levels and the population distribution, and find the atoms to be localized to 1/15 of the optical wave-length. We find up to 60% of the population of trapped atoms in the vibrational ground state. The dependence of the spectrum on the parameters of the optical field provides detailed information about the dynamics of laser-cooled atoms.
 

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Generation of a frequency comb with a double acousto-optic modulator ring

Poul Jessen and Martin Kristensen

Institute of Physics and Astronomy, University of Aarhus, DK-8000 Århus, C Denmark
 

We use an acousto-optic modulator ring setup to impose an asymmetric frequency comb on a dye laser. Applications include laser cooling of stored heavy ions.
 

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Laser-rf double-resonance spectroscopy in a storage ring

M. Kristensen, J. S. Hangst, P. S. Jessen, J. S. Nielsen, O. Poulsen, and P. Shi

Institute of Physics and Astronomy, University of Aarhus, DK-8000 Århus, C Denmark
 

Laser-rf double-resonance spectroscopy of the hyperfine transition between F”=0 and F’= 1 in the metastable ‘Sl state of Li+ was performed in 100-keV beam in the storage ring ASTRID. High efficiency of optical pumping was demonstrated for complex pumping schemes. A broadband (dc —6 GHz) rf device was designed and used for rf spectroscopy in the storage ring. The possibility of obtaining coherent rf signals (Ramsey fringes) from successive interactions with the same field was investigated. Important limitations for the coherences due to magnetic-field inhomogeneities were observed. These led to randomization of the atomic polarization during only one turn in the storage ring and completely prevented observation of Ramsey fringes. This situation is different from the case of fundamental particles in a storage ring, where the polarization may be preserved for many round-trips. Limits were put on the demands to beam quality, beam positioning, and magnetic-field quality to overcome the problem. The effects of the rf device on the external degrees of freedom of the ion beam were investigated. Its small aperture substantially reduced the beam lifetime, and at very low rf frequencies the electric field in the rf device was able to excite external transverse resonances in the beam.
 

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The Temperature of Optical Molasses for Two Different Atomic Angular Momenta

C. Gerz,¹ T. W. Hodapp,¹ P. Jessen,¹ K. M. Jones,¹ W. D. Phillips,¹ C. I. Westbrook,¹ and K. Mølmer²

1. National Institute of Standards and Technology, U.S. Department of Commerce,
Technology Administration – PHYS A167, Gaithersburg, MD 20899, USA
2. Max Planck Institut für Quantenoptik – Garching, Germany
 

We have measured the temperature of laser-cooled Rb atoms in optical molasses as a function of laser intensity and detuning. For both @’Rb and s7Rb, cooled on the F = 3 + F’ = 4 and F = 2 + F ‘ = 3 transitions, respectively, the temperatures are proportional to the ratio of laser power and detuning for a wide range of these parameters. We observe a small but significant difference between the two isotopes. We also show the results of three-dimensional semi-classical numerical calculations. Our results favor a model which includes atomic localization in optical standing waves.
 

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Trotter Errors and the Emergence of Chaos in Quantum Simulation 

Kevin W. Kuper,¹ Jon Pajaud,¹ Karthik Chinni,² Pablo Poggi,² and Poul S. Jessen¹

1. Wyant College of Optical Sciences, University of Arizona, Tucson, AZ 85721, USA
2. Center for Quantum Information and Control, Department of Physics and Astronomy,
University of New Mexico, Albuquerque, NM 87131, USA
 

As noisy intermediate-scale quantum (NISQ) processors increase in size and complexity, their use as general purpose quantum simulators will rely on algorithms based on the Trotter-Suzuki expansion. We run quantum simulations on a small, highly accurate quantum processor, and show how one can optimize simulation accuracy by balancing algorithmic (Trotter) errors against native errors specific to the quantum hardware at hand. We further study the interplay between native errors, Trotter errors, and the emergence of chaos as seen in measurements of a time averaged fidelity-out-of-time-ordered-correlator.
 

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Squeezing the angular momentum of an ensemble of complex multi-level atoms

 

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D. Hemmer¹, E. Montaño¹, B. Q. Baragiola^2,3, L. M. Norris³, E. Shojaee³, I. H. Deutsch³, and P. S. Jessen¹

1. Center for Quantum Information and Control, University of Arizona, Tucson, Arizona 85721, USA
2. Centre for Quantum Computation and Communication Technology,
School of Science, RMIT University, Melbourne, Victoria 3001, Australia
3. Center for Quantum Information and Control, University of New Mexico,
Albuquerque, New Mexico 87131, USA
 

Squeezing of collective atomic spins has been shown to improve the sensitivity of atomic clocks and magnetometers to levels significantly below the standard quantum limit. In most cases the requisite atom-atom entanglement has been generated by dispersive interaction with a quantized probe field or by state-dependent collisions in a quantum gas. Such experiments typically use complex multilevel atoms like Rb or Cs, with the relevant interactions designed so that atoms behave like pseudospin- 1/2 particles. We demonstrate the viability of spin squeezing for collective spins composed of the physical angular momenta of 106 Cs atoms, each in an internal spin-4 hyperfine state. A peak metrological squeezing of at least 5dB is generated by quantum backaction from a dispersive quantum nondemolition (QND) measurement, implemented using a two-color optical probe that minimizes tensor light shifts without sacrificing measurement strength. Other significant developments include the successful application of composite pulse techniques for accurate dynamical control of the collective spin, enabled by broadband suppression of background magnetic fields inside a state-of-the-art magnetic shield. The absence of classical noise allows us to compare the observed quantum projection noise and squeezing to a theoretical model that properly accounts for both the relevant atomic physics and the spatial mode of the collective spin, finding good quantitative agreement and thereby validating its use in other contexts. Our work sets the stage for experiments on quantum feedback, deterministic squeezing, and closed-loop magnetometry. The implementation of real-time feedback may also create an opportunity for new types of quantum simulation, wherein the evolution of a quantum system is conditioned on the outcome of a time-continuous QND measurement. Such a scheme has the potential to access new regimes near the quantum-classical boundary, with opportunities to study long-standing issues related to quantum-classical correspondence in chaotic systems.

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Quantifying the sensitivity to errors in analog quantum simulation

 

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P. M. Poggi¹, N. K. Lysne², K. W. Kuper², I. H. Deutsch¹, and P. S. Jessen²

1. Center for Quantum Information and Control (CQuIC), Department of Physics and Astronomy,
University of New Mexico, Albuquerque, New Mexico 87131, USA
2. Center for Quantum Information and Control (CQuIC), Wyant College of Optical Sciences,
University of Arizona, Tucson, Arizona 85721, USA
 

Quantum simulators are widely seen as one of the most promising near-term applications of quantum technologies. However, it remains unclear to what extent a noisy device can output reliable results in the presence of unavoidable imperfections. Here we propose a framework to characterize the performance of quantum simulators by linking robustness of quantum expectation values to the spectral properties of the output observable, which in turn can be associated with its macroscopic or microscopic character. We show that, under general assumptions and on average over all states, imperfect devices are able to reproduce the dynamics of macroscopic observables accurately, while the relative error in the expectation value of microscopic observables is much larger on average. We experimentally demonstrate the universality of these features in a state-of-the-art quantum simulator and show that the predicted behavior is generic for a highly accurate device, without assuming any knowledge about the nature of the imperfections.
 

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