David W. Landgren

Demonstration of integrated microscale optics in surface-electrode ion traps

In ion trap quantum information processing, efficient fluorescence collection is critical for fast, high-fidelity qubit detection and ion–photon entanglement. The expected size of future many-ion processors requires scalable light collection systems. We report on the development and testing of a microfabricated surface-electrode ion trap with an integrated high-numerical aperture (NA) micromirror for fluorescence collection. When coupled to a low-NA lens, the optical system is inherently scalable to large arrays of mirrors in a single device. We demonstrate the stable trapping and transport of 40Ca+ ions over a 0.63 NA micromirror and observe a factor of 1.9 enhancement of photon collection compared to the planar region of the trap.

Reliable transport through a microfabricated X-junction surface-electrode ion trap

We report the design, fabrication and characterization of a micro- fabricated surface-electrode ion trap that supports controlled transport through the two-dimensional intersection of linear trapping zones arranged in a 90 cross. The trap is fabricated with very large scalable integration techniques which are compatible with scaling to a large quantum information processor. The shape of the radio-frequency electrodes is optimized with a genetic algorithm to reduce axial pseudopotential barriers and minimize ion heating during transport. Seventy-eight independent dc control electrodes enable fine control of the trapping potentials. We demonstrate reliable ion transport between junction legs and determine the rate of ion loss due to transport. Doppler-cooled ions survive more than 10 5 round-trip transits between junction legs without loss and more than 65 consecutive round trips without laser cooling.

FDTD in curvilinear coordinates using a rectangular FDTD formulation

In the simplest formulation, the FDTD algorithm requires that objects follow the rectangular grid. For curved surfaces, this is a severe limitation. In this paper, an approach to modify an existing rectangular FDTD code to model structures more naturally described in another coordinate system is demonstrated. The approach is a modification to the update coefficients and does not require significant changes to an existing piece of software.

Integration of an X-band antenna array with high power photodiodes

Demonstration of low conversion loss through the novel integration and packaging of high power photodiodes and a fragmented aperture antenna for a fiber-fed RF array.

Genetic algorithms for fragmented aperture antennas: A complete evaluation of a 24-bit design

Summary form only given. GTRI has a long history pioneering a wideband antenna concept known as the fragmented aperture (FA). Unlike other concepts that use scale invariance to utilize a specific region of the aperture that changes with frequency (known as the active region), the FA is designed to utilize the entire aperture over the entire frequency band. The result is that FA antennas routinely approach the theoretical limit of antenna performance based on a uniformly illuminated aperture. However, because FAs consist of complex printed metallic patterns on single or multi layer substrates, the design necessarily is heavily simulation driven. Our proprietary design processes have been very successful in designing apertures for a wide variety of applications. The metallic pattern is described using a binary code (typically hundreds of bits), and the pattern is designed using a genetic algorithm on a large computer cluster. Because the design space for these antennas is enormous, it is unclear if a well-designed “good” antenna is near the best possible antenna. An additional question is whether or not our genetic search algorithms are efficiently searching the design space. To address these questions, over a decade ago GTRI researchers created a very limited antenna design that could be described using only 18 bits. Every possible antenna in this space was evaluated and algorithm convergence was proven. In the last decade, computers have been much more powerful, and our design process has evolved to allow much more complicated patterns. To update the previous results, ACL researchers recently used a large computer cluster to evaluate every possible antenna in a 24-bit design (2^24 possible antennas, which is 64 times larger than the previous dataset). The evaluation took nearly a month of cluster time and produced gigabytes of simulation results. Using this library of known solutions, we can quickly test design algorithms for convergence time. The encoding strategy is shown below. Bits 1-23 specify on/off regions of metal. The 24th bit specifies a choice of two feed regions (compare the cells marked 24 below). Detailed results based on this dataset will be presented at the conference.