Physics
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Item Experiments with Trapped Ions and Ultrafast Laser Pulses(2016) Johnson, Kale Gifford; Monroe, Christopher; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Since the dawn of quantum information science, laser-cooled trapped atomic ions have been one of the most compelling systems for the physical realization of a quantum computer. By applying qubit state dependent forces to the ions, their collective motional modes can be used as a bus to realize entangling quantum gates. Ultrafast state-dependent kicks [1] can provide a universal set of quantum logic operations, in conjunction with ultrafast single qubit rotations [2], which uses only ultrafast laser pulses. This may present a clearer route to scaling a trapped ion processor [3]. In addition to the role that spin-dependent kicks (SDKs) play in quantum computation, their utility in fundamental quantum mechanics research is also apparent. In this thesis, we present a set of experiments which demonstrate some of the principle properties of SDKs including ion motion independence (we demonstrate single ion thermometry from the ground state to near room temperature and the largest Schrodinger cat state ever created in an oscillator), high speed operations (compared with conventional atom-laser interactions), and multi-qubit entanglement operations with speed that is not fundamentally limited by the trap oscillation frequency. We also present a method to provide higher stability in the radial mode ion oscillation frequencies of a linear radiofrequency (rf) Paul trap--a crucial factor when performing operations on the rf-sensitive modes. Finally, we present the highest atomic position sensitivity measurement of an isolated atom to date of ~0.5 nm Hz^(-1/2) with a minimum uncertainty of 1.7 nm using a 0.6 numerical aperature (NA) lens system, along with a method to correct aberrations and a direct position measurement of ion micromotion (the inherent oscillations of an ion trapped in an oscillating rf field). This development could be used to directly image atom motion in the quantum regime, along with sensing forces at the yoctonewton [10^(-24) N)] scale for gravity sensing, and 3D imaging of atoms from static to higher frequency motion. These ultrafast atomic qubit manipulation tools demonstrate inherent advantages over conventional techniques, offering a fundamentally distinct regime of control and speed not previously achievable.Item Ultra-fast Dynamics of Small Molecules in Strong Fields(2006-04-24) Zhao, Kun; Hill, Wendell T; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Correlation detection techniques (image labeling, coincidence imaging, and joint variance) are developed with an image spectrometer capable of collecting charges ejected over 4\pi sr and a digital camera synchronized with the laser repetition rate at up to 735 Hz. With these techniques, molecular decay channels ejecting atomic fragments with different momenta (energies) can be isolated; thus the initial molecular configurations (bond lengths and/or bond angles) and orientations as well as their distributions can be extracted. These techniques are applied to study strong-field induced dynamics of diatomic and triatomic molecules. Specific studies included the measurements of the Coulomb explosion energy as a function of bond angle in linear (CO_2) and bent (NO_2) triatomics and the ejection anisotropy relative to the laser polarization axis during Coulomb explosions in both triatomic (CO_2 and NO_2) and diatomic (H_2, N_2 and O_2) systems. The experiments were performed with 100 fs, 800 nm laser pulses focused to 0.1 ~ 5 \times 10^15 W/cm^2. The explosion energy of NO_2 decreases monotonically by more than 25% from the smallest to the largest bond angle. By contrast, the CO_2 explosion energies are nearly independent of bond angle. The enhanced-ionization and static-screening models in two-dimension with three charge centers were developed to simulate the explosion energies as a function of bond angle. The predictions are consistent with the measurements of CO_2 and NO_2. The observed explosion signals as a function of bond angle for both triatomics show large-amplitude vibrations. The ejection angular distributions in triatomic (CO_2 and NO_2) and diatomic (H_2, N_2, and O_2) Coulomb explosions were measured; the contribution made to the ejection anisotropy by dynamic alignment was studied by comparing the images obtained with linearly and circularly polarized fields. Different angular distributions of the molecules are consistent with different ionization stages, induced dipole moments and rotational constants. The dynamic alignment of H_2 is found to be nearly complete. A larger dynamic alignment of CO_2 than that of N_2 or O_2 is consistent with that more electrons have been removed from CO_2 and the precursor molecular ion spends more time in the field prior to the explosion.