Michael Ramm

Trapped ions in optical lattices for probing oscillator chain models

We show that a chain of trapped ions embedded in microtraps generated by an optical lattice can be used to study oscillator models related to dry friction and energy transport. Numerical calculations with realistic experimental parameters demonstrate that both static and dynamic properties of the ion chain change significantly as the optical lattice power is varied. Finally, we lay out an experimental scheme to use the spin degree of freedom to probe the phase space structure and quantum critical behavior of the ion chain.

Local detection of quantum correlations with a single trapped ion

In open quantum systems the correlations between the system and its environment play an important role. A trapped-ion experiment demonstrates that these correlations can be detected without accessing or knowing anything about the environment or its interactions.

Michelson-Morley analogue for electrons using trapped ions to test Lorentz symmetry

T. Pruttivarasin,1, 2 M. Ramm,1 S. G. Porsev,3, 4 I. I. Tupitsyn,5 M. Safronova,3, 6 M. A. Hohensee,1, 7 and H. Häffner1 1Department of Physics, University of California, Berkeley, California 94720, USA 2Quantum Metrology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan 3Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA 4Petersburg Nuclear Physics Institute, Gatchina, Leningrad District 188300, Russia 5Department of Physics, St. Petersburg State University, Ulianovskaya 1, Petrodvorets, St.Petersburg 198504, Russia 6Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, College Park, Maryland, 20742, USA 7Lawrence Livermore National Laboratory, Livermore, California 94550, USA (Dated: December 11, 2014)

Energy transport in trapped ion chains

We experimentally study energy transport in chains of trapped ions. We use a pulsed excitation scheme to rapidly add energy to the local motional mode of one of the ions in the chain. Subsequent energy readout allows us to determine how the excitation has propagated throughout the chain. We observe energy revivals that persist for many cycles. We study the behavior with an increasing number of ions of up to 37 in the chain, including a zig-zag configuration. The experimental results agree with the theory of normal mode evolution. The described system provides an experimental toolbox for the study of thermodynamics of closed systems and energy transport in both classical and quantum regimes.

Precision Measurement Method for Branching Fractions of Excited P1/2 States Applied to 40Ca+

We present a method for measuring branching fractions for the decay of J=1/2 atomic energy levels to lower-lying states based on time-resolved recording of the atoms fluorescence during a series of population transfers. We apply this method to measure the branching fractions for the decay of the 4²P(1/2) state of 40Ca+ to the 4²S(1/2) and 3²D(3/2) states to be 0.935 65(7) and 0.064 35(7), respectively. The measurement scheme requires that at least one of the lower-lying states be long lived. The method is insensitive to fluctuations in laser light intensity and magnetic field and is readily applicable to various atomic species due to its simplicity. Our result distinguishes well among existing state-of-the-art theoretical models of Ca+.

Observing a quantum phase transition by measuring a single spin

We show that the ground-state quantum correlations of an Ising model can be detected by monitoring the time evolution of a single spin alone, and that the critical point of a quantum phase transition is detected through a maximum of a suitably defined observable. A proposed implementation with trapped ions realizes an experimental probe of quantum phase transitions which is based on quantum correlations and scalable for large system sizes.

Local probe of single phonon dynamics in warm ion crystals

The detailed characterization of non-trivial coherence properties of composite quantum systems of increasing size is an indispensable prerequisite for scalable quantum computation, as well as for understanding non-equilibrium many-body physics. Here, we show how autocorrelation functions in an interacting system of phonons as well as the quantum discord between distinct degrees of freedoms can be extracted from a small controllable part of the system. As a benchmark, we show this in chains of up to 42 trapped ions, by tracing a single phonon excitation through interferometric measurements of only a single ion in the chain. We observe the spreading and partial refocusing of the excitation in the chain, even on a background of thermal excitations. We further show how this local observable reflects the dynamical evolution of quantum discord between the electronic state and the vibrational degrees of freedom of the probe ion.

Direct spectroscopy of the 2S1/2 − 2P1/2 and 2D3/2 − 2P1/2 transitions and observation of micromotion modulated spectra in trapped 40Ca+

We present an experimental scheme to perform spectroscopy of the

Probing surface electric field noise with a single ion

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Local Detection of Quantum Correlations with a Trapped Ion

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