String order via Floquet interactions in atomic systems

We study the transverse-field Ising model with interactions that are modulated in time. In a rotating frame, the system is described by a time-independent Hamiltonian with many-body interactions, similar to the cluster Hamiltonians of measurement-based quantum computing. In one dimension, there is a three-body interaction, which leads to string order instead of conventional magnetic order. We show that the string order is robust to power-law interactions that decay with the cube of distance. In two and three dimensions, there are five- and seven-body interactions. We discuss adiabatic preparation of the ground state as well as experimental implementation with trapped ions, Rydberg atoms, and polar molecules.Comment: 8 pages, 6 figure

Trapped Antihydrogen in Its Ground State

Antihydrogen atoms $(\bar{H})$ are confined in a magnetic quadrupole trap for 15 to 1000 s - long enough to ensure that they reach their ground state. This milestone brings us closer to the long-term goal of precise spectroscopic comparisons of $\bar{H}$ and H for tests of CPT and Lorentz invariance. Realizing trapped $\bar{H}$ requires characterization and control of the number, geometry, and temperature of the antiproton $(\bar{p})$ and positron $(e^+)$ plasmas from which $\bar{H}$ is formed. An improved apparatus and implementation of plasma measurement and control techniques make available $10^7 \bar{p}$ and $4 \times 10^9 e^+$ for $\bar{H}$ experiments - an increase of over an order of magnitude. For the first time, $\bar{p}$ are observed to be centrifugally separated from the electrons that cool them, indicating a low-temperature, high-density $\bar{p}$ plasma. Determination of the $\bar{p}$ temperature is achieved through measurement of the $\bar{p}$ evaporation rate as their confining well is reduced, with corrections given by a particle-in-cell plasma simulation. New applications of electron and adiabatic cooling allow for the lossless reduction in $\bar{p}$ temperature from thousands of Kelvin to 3.5 K or colder, the lowest ever reported. The sum of the 20 trials performed in 2011 in which $\bar{p}$ and $e^+$ mix to form $\bar{H}$ in the presence of a magnetic quadrupole trap reveals a total of $105 \pm 21$ trapped $\bar{H}$, or $5 \pm 1$ per trial on average. This result paves the way towards the large numbers of simultaneously trapped $\bar{H}$ that will be necessary for laser spectroscopy.Physic

Depletion, quantum jumps, and temperature measurements of ⁸⁸Sr⁺ ions in a linear Paul Trap

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (leaves 115-121).This thesis describes the design and construction of two laser systems to probe the 674nm transition of ⁸⁸Sr⁺ ions in a linear Paul trap. The first laser system made use of a molecular transition in Iodine to stabilize the length of a Fabry-Perot cavity for laser locking. After constructing this laser, we measured an unsuitable experimental stability of 10 MHz over 5 minutes. A completely new monolithic laser system was built, providing better environmental isolation and a frequency stability of at least 1 MHz over 5 minutes. Using this laser, we were able to observe depletion and quantum jump effects in our ion trap system. Additionally, by scanning the red laser frequency, we were able to see the blue-laser broadened spectrum of the 674nm transition. Fitting the spectrum to a Voigt function yielded an ion temperature of 35 mK. To avoid blue-broadening, we set up blue and red laser pulse sequences. This allowed us to observe a red spectrum with secular sidebands and calculate an ion temperature of 6.8 +4.4 / -2.2 mK.by Philip J. RichermeS.B

Quantum Catalysis of Magnetic Phase Transitions in a Quantum Simulator

We control quantum fluctuations to create the ground state magnetic phases of a classical Ising model with a tunable longitudinal magnetic field using a system of 6 to 10 atomic ion spins. Due to the long-range Ising interactions, the various ground state spin configurations are separated by multiple first-order phase transitions, which in our zero temperature system cannot be driven by thermal fluctuations. We instead use a transverse magnetic field as a quantum catalyst to observe the first steps of the complete fractal devil's staircase, which emerges in the thermodynamic limit and can be mapped to a large number of many-body and energy-optimization problems.Comment: New data in Fig. 3, and much of the paper rewritte