A single Ba-137(+) ion has been laser cooled to the first few vibrational states of an 80-mum radius rf quadrupole trap. Initial measurements showed no anomalous heating of the vibrational phonon for observation times up to 1 ms, corresponding to a heating rate less than 3.3 phonons/ms at a 95% confidence level. Subsequently we observed the growth of large and unstable bias voltages that were correlated with exposure to the atomic beam. After loading over 250 ions over a period of 720 days the trap became unstable, with ion lifetimes <1 min. A possible connection between this trap instability and anomalous heating observed in quantum computation experiments is discussed. An isotopically selectively laser cooling method was used to refine Ba-137 ions out of a naturally abundant cloud.

The heating rate of ions laser cooled to the vibrational ground state of an rf quadrupole trap provide sensitive limits on partition noise (shot noise) of the rf current in the trap electrodes. The millisecond lifetimes observed in recent experiments correspond to a partition noise power spectral density (Fano factor) less than 10 - 8 of the Poisson value, showing a sensitivity > 10 6 greater than the solid-state measurements.

Summary form only given. We report on the trapping and laser cooling ofa single /sup 137/Ba/sup +/ ion on a transition to the 2p/sub 3/2/ level at a wavelength of 493 nm from a mixed isotopic Ba source with a natural abundance of 11% of /sup 137/Ba.

The properties of a rf quadrupole trap, the elliptical ion trap, are derived. Elliptical traps can confine large numbers of ions in the Lamb-Dicke regime due to a hitherto unrecognized mechanism unique to one-dimensional Coulomb crystals, implicit in the theories of Dubin and Schiffer. This follows from a linear crystal stability condition, which uniquely relates the crystal size to ellipticity, and a micromotion relation, which reveals a 1/5-root dependence on the number of trapped ions. Elliptical traps offer several advantages over linear traps in the Cirac-Zoller model of quantum computing, both for initial tests and as a potential method of creating a full-scale quantum computer. Numerical solutions of a one-electrode structure show that microscopic elliptical traps, each containing approximate to 100 ions, can be constructed at a density of 100 traps/cm(2), making possible arrays containing >10(6) ions in the Lamb-Dicke regime for precision spectroscopy or quantum computation. [S1050-2947(98)08008-1].

A new class of photochromic glasses for use in irreversible holographic optical storage applications is described. The recording mechanism involves a triplet-sensitized photoreaction of an organic chromophore. The materials are isotropic and red-sensitive, and exhibit high diffraction efficiencies and long hologram lifetimes. The wavelength sensitivity can be adjusted by the choice of sensitizer; C60, sensitive in the red, is described here. Single digital data page recording and error-free readout are demonstrated at a density of 0.5 Mb/cm2; multiplexing in a 150-μm-thick sample is also demonstrated.

We report high-contrast storage of 64-kbit digital data pages in a photorefractive polymer material. Singlepage writing, reading, and erasing operations were demonstrated with a dual-function-dopant polymeric material having a dark lifetime of several days. Data were reconstructed without error by use of several simple readout algorithms.

Summary form only given. We report a laboratory realization of the gedanken experiment that Dicke used to introduce superradiance. Two Ba/sup +/ ions are laser-cooled and crystallized in a microscopic Paul trap so that they come to rest 1.5 microns from each other. This is about 3 wavelengths of the 493 nm light used to laser cool the transition. Micromotion and residual thermal motion are low so that they are essentially stationary relative to 493 nm light.

It is demonstrated that the microscopic mechanism of the photorefractive (PR) effect in organic composites with low glass transition temperatures involves the formation of refractive index gratings through a space-charge field-modulated Kerr effect. A tensorial formulation of the macroscopic aspects of the PR Kerr effect and its microscopic interpretation is presented. The second-order dipole orientation term containing the anisotropy of the first-order optical polarizability α(−ω;ω) is shown to yield the dominant contribution to the Kerr susceptibility χ(3)(−ω;ω,0,0). A class of special chromophores having negligible second-order polarizabilities β(−ω;ω,0) and large dipole moments μ has been identified in order to optimize this term. These chromophores are not subject to the efficiency-transparency tradeoff typically encountered with second-order nonlinear optical (NLO) chromophores, providing highly transparent materials with large PR Kerr response. Contrary to previous approaches in this field, the best-performing PR polymers are then expected to employ chromophores that would be useless for second- order applications (negligible β). We report PR of the material 30% 2,6-di-n-propyl-4H-pyran-4-ylidenemalononitrile (DPDCP): 15% N,N′-bis(3-methylphenyl)- N,N′-bis(phenyl)benzidine (TPD):55% poly(methyl methacrylate) (PMMA):0.3% C60 as an illustration of this principle. A 100 μm thick film of this material exhibits a steady-state diffraction efficiency of η=25% and net two-beam coupling of Γ=50 cm−1 at a bias field of 100 V/μm and a wavelength of 676 nm. The macroscopic Kerr susceptibility of the material is related to molecular electronic properties of the chromophore DPDCP which were independently determined by experiments in solution and by quantum chemical calculations.

In order to be useful in practical nonlinear optical(NLO) devices such as high speed optical switches and modulators, several key properties of electrooptic(EO) polymers must be optimized: the polymer's electrooptic response must be sufficiently large, the response must be stable at all temperatures that the polymer will experience in processing and in operation and the attenuation of light in the polymer by scattering and by absorption must be low. For the specific applications of on-chip and chip-to-chip active optical interconnects, the thermal stability requirements are particularly severe. During the processes of microprocessor die attachment and hermetic packaging, the EO polymer will experience temperatures of >300°C for several minutes[1]. We have investigated the potential and limitations of electrooptic polymers under these severe thermal conditions, proceeding from the identification of NLO chromophores with high intrinsic molecular hyperpolarizabilities[2], incorporation into thermally stable polymers[3][4], and fabrication into electrooptic switches and devices[5].

In this communication we take up the age-old problem of the possibility to incorporate quantum jumps. Unusually, we investigate quantum jumps in an extended quantum setting, but one of rigorous mathematical significance. The general background for this formulation originates in the Balslev-Combes theorem for dilatation analytic Hamiltonians and associated complex symmetric representations. The actual jump is mapped into a Jordan block of order two and a detailed derivation is discussed for the case of the emission of a photon by an atom. The result can be easily reassigned to analogous cases as well as generalized to Segrè characteristics of arbitrary order.

A time-correlated single-photon counting method is used to measure the spontaneous emission lifetime of a single trapped barium ion, yielding a standard deviation of 0.5% for 8 min of integration time. The statistical power of this one-atom technique is comparable with that of other methods that use a macroscopic sample, but the technique has potentially lower systematic errors. The method depends on the use of an electro-optic phase modulator as an Nth-order nonlinear switch, which improves the response time by a factor of N and the on–off ratio by the Nth power.

Laser-cooled trapped ion crystals offer a unique opportunity to study the interactions between atoms. We have previously developed a microscopic planar Paul trap1 which is small and strong enough to bring the ion separation into the sub-micron region where quantum collective effects become important. A search is underway for the superradiant coupling of two atoms which manifests itself as a variation of the spontaneous emission rate with the ion-ion distance. We have produced an ion crystal with a separation of 1.1 microns in an 80 micron radius planar Paul trap. At this distance, equal to 2.2 wavelengths of the 493 nm Ba + transition, superradiant effects should alter the decay rate by about 10%. The two-ion crystal is imaged with sub-micron resolution by a new diffraction-limited vacuum-compatible microscope. The spontaneous emission rate is measured by a high repetition-rate transient spectrometer with an error of less than 1% for a single ion in a few minutes. Efficient extinction of the exciting laser light is provided by a new nonlinear electrooptic sideband switch.

We report the laser cooling and trapping of barium ions in a novel planar Paul trap. Unlike other rf quadrupole traps, the electrodes of a planar Paul trap are confined to one or more parallel planes. They may therefore be constructed on a micrometer scale by the same photolithographic techniques used for semiconductor devices. Such devices are under construction in our laboratory. Micro-traps permit entirely new studies, for example, superradiance of a few ions, which occurs as ion-ion distances approach one wavelength of light. Photolithography can also generate an array of traps on a single substrate for an atomic clock. Our traps consist of one or more parallel planes, one above the other, each plane having either a conducting ring or a hole in a conducting sheet. Thus, a ring or a hole results in a potential well for trapping. A three-ring design produces a quadrupole potential that is harmonic up to eighth-order for a particular choice of ring diameters and spacings. Three-hole traps have been constructed with inner hole radii ranging from 50 to 400 μm, and both single barium ions and clouds have been observed.

Transient order\ensuremath{\rightarrow}chaos transitions of two ${\mathrm{Ba}}^{+}$ ions are observed where the duration of the chaotic state increases smoothly with an increasing Mathieu control parameter q. The transient regime precedes the transition point ${\mathit{q}}_{\mathit{c}}$ for stationary chaos, which is well defined and reproducible. The perturbative step that initiates chaos takes place on a time scale of 1 min, far longer than previous estimates, and is due to a single ${\mathrm{H}}_{2}$-${\mathrm{Ba}}^{+}$ collision (${\mathrm{H}}_{2}$ pressure 5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ Torr). In contrast to random collision events, chaos can be initiated deterministically by a new pulse technique. These observations resolve earlier anomalies and challenge computer simulations.

Two ions confined to a radio-frequency trap and cooled by radiation pressure exhibit deterministic chaos. Theoretical analysis of the two-ion dynamics reveals that the route to chaos is due solely to ion-ion collisions. During a collision, the nonlinear Coulomb interaction introduces a transient instability, which gives way to stable single-particle-like motion as the ions move apart. The chaotic dynamics are characterized by a strange attractor that resembles a spiral galaxy.

We have stabilized the frequency of a commercial ring dye laser operating in the blue near 486 nm with an internal electro-optic modulator, using optical heterodyne detection of phase-modulated light reflected from a reference cavity. With a servo bandwidth of 10 MHz, the short-term stability has been reduced below 1 kHz. Frequency doubling of this laser will provide highly monochromatic 243 nm radiation for high resolution spectroscopy of the two-photon hydrogen 1S–2S transition.

We are reporting on major progress in the development of a blue ring dye laser with extreme frequency stability. With improvements of the reference cavity and servo electronics, we have reduced the locking error from a previously reported sub-kHz level to less than 1 Hz. Frequency doubling of this laser will provide narrow bandwidth 243-nm radiation for high precision experiments of the two-photon hydrogen atom 1S-2S transition which has an extremely narrow natural linewidth of 1.3 Hz.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text M. A. Kasevich, E. Riis, S. Chu, and R. G. DeVoe, "Atomic fountains and clocks," Optics News 15(12), 31-32 (1989) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Laser-cooled sodium atoms pushed up on a vertical trajectory by radiation pressure are observed to turn around due to gravity. The reatively long time the atoms spent freely falling in this ``atomic fountain'' allowed the ground-state hyperfine splitting to be measured with a linewidth of 2 Hz. After a 1000-s integration time, the center of the line was resolved to \ifmmode\pm\else\textpm\fi{}10 mHz. The absolute splitting was measured to be 1 771 626 129(2) Hz.