Session F6: Atomic Physics

A laser-cooled single-atom-on-demand source for Si quantum computing

A promising proposal by B. Kane for a scalable silicon quantum computer requires the placement of P-31 atoms 20 nm apart and 10 nm below the surface in pure Si-28 to 1 nm precision. Attempts to do this with 10-30 keV P-31 beams have not yet succeeded. This paper presents a scheme for laser cooling and trapping Si-31 atoms in a magneto-optical trap (MOT), detecting by fluorescence when there is only one atom in the trap, resonantly ionizing that one atom near threshold, and softly depositing the single 31Si+ ion in Si to nm precision at $\sim $100 eV. A few hours after deposition Si-31 beta decays in situ to the desired species 31P+. The hyperfine structure and isotope shifts of the 221.7 nm cooling transition for the stable isotopes of Si have been measured with precision for the first time. Additional progress, including demonstration of sufficient power at 221.7 nm for the MOT will also be reported.   

Detection of new auto-ionizing states of $^{28}$Si using resonant ionization

We are developing a scalable, solid state, quantum computer based on the Kane proposal of using $^{31}$P$^{+}$ donor ions in Si as qubits. This involves the placement of P$^{+}$ into a Si substrate with nm precision. We plan to accomplish this by laser cooling and trapping single, ablated, radioactive, $^{31}$Si atoms in a magneto-optical trap (MOT) prior to implanting them into a Si substrate. $^{31}$Si subsequently beta decays into $^{31}$P$^{+}$, forming the qubit. To gain experience before handling short lived, low abundance radioactive materials the techniques to make these measurements are being developed on $^{28}$Si. In this talk we will report on measurements of $^{28}$Si resonance ionization spectroscopy near the first ionization limit, including newly discovered auto-ionizing states. These states were detected by scanning a pulsed dye laser across a beam of excited atoms. Using this method we generated a saturation curve and calculated the photoionization cross section for the lowest lying state above the ionization limit. Additionally we will report on initial studies of laser ablation of a solid silicon sample. Research supported by the W. M. Keck Foundation and the National Science Foundation. {\dag}Fellowship support provided by the U.S. Military Academy, West Point, NY.   

Polarizability of Pb III from spectroscopy of high-L Rydberg states of Pb II

Using the Resonant Excitation Stark Ionization Spectroscopy technique[1], we measured resolved fine structure components of the n=20 to n'=52 transition in Pb$^{+}$, and determined the polarizability of Pb$^{2+}$. A critical part of the measurement consists of the determination of the L-value of one or more of the resolved excitation peaks. These measurements were motivated by a discrepancy between previous polarizability determinations based on contrasting methods[2]. \\[4pt] [1] S.R. Lundeen and C.W. Fehrenbach, Phys. Rev. A 75, 032523 (2007) \\[0pt] [2] Nicholas Reshetnikov, et. al., Physica Scripta 77, 015301 (2008).   

The Doubling of 846 nm Light to Produce 423 nm Light for use in Atom Interferometry

We present progress on a 423 nm fluorescence probe/cooling laser for use in our neutral calcium atom interferometer. The finished system will include an 846 nm diode laser that is coupled to a tapered amplifier. This light will be sent to a buildup cavity where we will achieve second-harmonic generation (SHG) using either a BBO non-linear crystal or a periodically-poled KTP crystal. We will discuss the theoretical considerations relating to the doubling of light in a crystal and the construction of our buildup cavity. We will also discuss its proposed application for use in atom interferometry.   

Can spin-up go down in a Stern-Gerlach device? The propagator approach to Stern-Gerlach wavepacket dynamics

The Stern-Gerlach effect (SGE) is iconic for visualizing spin. We analyze the evolution of atomic wavepackets by constructing exact solutions using propagators in SGE field configurations in different approximations. We contrast our results with the standard presentation of the SGE in textbooks and literature and illustrate with visual animations in 2D and 3D.   

Center-of-Mass Technique applied to the Ideal Inelastic Collisions Case

Findings show that the law of conservation of kinetic energy directly applies to inelastic collisions as well as to elastic collisions. The kinetic energy transfer is consistent with the law of conservation of energy which states that energy can neither be created nor annihilated. In an ideal inelastic collision, two colliding masses, M$_{1}$ and M$_{2}$, will move jointly at their center-of-mass velocity, $V_{CM} =\textstyle{{M_1 V_1 +M_2 V_2 } \over {M_1 +M_2 }}$. As a consequence, the equation $\textstyle{1 \over 2}M_1 V_1 ^2+\textstyle{1 \over 2}M_2 V_2 ^2-\textstyle{1 \over 2}M_1 \left( {V_1 -V_{CM} } \right)^2-\textstyle{1 \over 2}M_2 \left( {V_2 -V_{CM} } \right)^2=\textstyle{1 \over 2}\left( {M_1 +M_2 } \right)V_{CM} ^2$ applies to the ideal inelastic collision. The quantities $\textstyle{1 \over 2}M_1 V_1 ^2$ and $\textstyle{1 \over 2}M_2 V_2 ^2$ are the initial kinetic energies of the masses M$_{1}$ and M$_{2}$, respectively, that would be available in the rest frame if the two masses were to come to a complete stop, V$_{1 }$= 0 and V$_{2}$ = 0. The negative terms, $-\textstyle{1 \over 2}M_1 \left( {V_1 -V_{CM} } \right)^2$ and $-\textstyle{1 \over 2}M_2 \left( {V_2 -V_{CM} } \right)^2$, are the kinetic energies transferred into the center-of-mass frame as M$_{1}$ and M$_{2}$ go from velocities, V$_{1}$ and V$_{2}$ , respectively, to the velocity V$_{CM}$. The kinetic equation leads directly to the valid conservation of momentum equation $M_1 V_1 +M_2 V_2 =\left( {M_1 +M_2 } \right)V_{CM} $~, a mathematical proof that the kinetic energy is totally conserved for the ideal inelastic collision. For details: \underline {http://www.extinctionshift.com/SignificantFindingsInelastic.htm}