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Register a new userScalable Loading of a Two-Dimensional Trapped-Ion Array
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We describe rapid, random-access loading of a two-dimensional (2D) surface-electrode ion-trap array based on two crossed photo-ionization laser beams. With the use of a continuous flux of pre-cooled neutral atoms from a remotely-located source, we achieve loading of a single ion per site while maintaining long trap lifetimes and without disturbing the coherence of an ion quantum bit in an adjacent site. This demonstration satisfies all major criteria necessary for loading and reloading extensive 2D arrays, as will be required for large-scale quantum information processing. Moreover, the already high loading rate can be increased by loading ions in parallel with only a concomitant increase in photo-ionization laser power and no need for additional atomic flux.
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We compute the Rydberg spectrum of a single Ca$^+$ ion in a Paul trap by incorporating various internal and external coupling terms of the ion to the trap in the Hamiltonian. The coupling terms include spin-orbit coupling in Ca$^+$, charge (electron and ionic core) coupling to the radio frequency and static fields, ion-electron coupling in the Paul trap, and ion center-of-mass coupling. The electronic Rydberg states are precisely described by a one-electron model potential for e$^-$+Ca$^{2+}$, and accurate eigenenergies, quantum defect parameters, and static and tensor polarizabilities for a number of excited Rydberg states are obtained. The time-periodic rf Hamiltonian is expanded in the Floquet basis, and the trapping-field-broadened Rydberg lines are compared with recent observations of Ca$^+(23P)$ and Ca$^+(52F)$ Rydberg lines.
We provide a comprehensive theoretical framework for describing the dynamics of a single trapped ion interacting with a neutral buffer gas, thus extending our previous studies on buffer-gas cooling of ions beyond the critical mass ratio [B. Holtkemeier et al., Phys. Rev. Lett. 116, 233003 (2016)]. By transforming the collisional processes into a frame, where the ions micromotion is assigned to the buffer gas atoms, our model allows one to investigate the influence of non-homogeneous buffer gas configurations as well as higher multipole orders of the radio-frequency trap in great detail. Depending on the neutral-to-ion mass ratio, three regimes of sympathetic cooling are identified which are characterized by the form of the ions energy distribution in equilibrium. We provide analytic expressions and numerical simulations of the ions energy distribution, spatial profile and cooling rates for these different regimes. Based on these findings, a method for actively decreasing the ions energy by reducing the spatial expansion of the buffer gas arises (Forced Sympathetic Cooling).
We show that with a purely blue-detuned cooling mechanism we can densely load single neutral atoms into large arrays of shallow optical tweezers. With this ability, more efficient assembly of larger ordered arrays will be possible - hence expanding the number of particles available for bottom-up quantum simulation and computation with atoms. Using Lambda-enhanced grey molasses on the D1 line of 87Rb, we achieve loading into a single 0.63 mK trap with 89% probability, and we further extend this loading to 100 atoms at 80% probability. The loading behavior agrees with a model of consecutive light-assisted collisions in repulsive molecular states. With simple rearrangement that only moves rows and columns of a 2D array, we demonstrate one example of the power of enhanced loading in large arrays.
We report on three-dimensional optical trapping of single ions in an optical lattice formed by two counter-propagating laser beams. We characterize the trapping parameters of the standing wave using the ion as a sensor stored in a hybrid trap consisting of a radio-frequency (rf), a dc, and the optical potential. When loading ions directly from the rf into the standing-wave trap, we observe a dominant heating rate. Monte Carlo simulations confirm rf-induced parametric excitations within the deep optical lattice as the main source. We demonstrate a way around this effect by an alternative transfer protocol which involves an intermediate step of optical confinement in a single-beam trap avoiding the temporal overlap of the standing wave and the rf field. Implications arise for hybrid (rf/optical) and pure optical traps as platforms for ultra-cold chemistry experiments exploring atom--ion collisions or quantum simulation experiments with ions, or combinations of ions and atoms.
Scaling quantum information processors is a challenging task, requiring manipulation of a large number of qubits with high fidelity and a high degree of connectivity. For trapped ions, this could be realized in a two-dimensional array of interconnected traps in which ions are separated, transported and recombined to carry out quantum operations on small subsets of ions. Here, we use a junction connecting orthogonal linear segments in a two-dimensional (2D) trap array to reorder a two-ion crystal. The secular motion of the ions experiences low energy gain and the internal qubit levels maintain coherence during the reordering process, therefore demonstrating a promising method for providing all-to-all connectivity in a large-scale, two- or three-dimensional trapped-ion quantum information processor.
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