Clark Highstrete

Complementary planar terahertz metamaterials

Planar electric split ring resonator (eSRR) metamaterials and their corresponding inverse structures are designed and characterized computationally and experimentally utilizing finite element modeling and THz time domain spectroscopy. A complementary response is observed in transmission. Specifically, for the eSRRs a decrease in transmission is observed at resonance whereas the inverse structures display an increase in transmission. The frequency dependent effective complex dielectric functions are extracted from the experimental data and, in combination with simulations to determine the surface current density and local electric field, provide considerable insight into the electromagnetic response of our planar metamaterials. These structures may find applications in the construction of various THz filters, transparent THz windows, or THz grid structures ideal for constructing THz switching/modulation devices.

Design, Fabrication, and Experimental Demonstration of Junction Surface Ion Traps

We present the design, fabrication and experimental implementation of surface ion traps with Y-shaped junctions. The traps are designed to minimize the pseudopotential variations in the junction region at the symmetric intersection of three linear segments. We experimentally demonstrate robust linear and junction shuttling with greater than 106 round-trip shuttles without ion loss. By minimizing the direct line of sight between trapped ions and dielectric surfaces, negligible day-to-day and trap-to-trap variations are observed. In addition to high-fidelity single-ion shuttling, multiple-ion chains survive splitting, ion-position swapping and recombining routines. The development of two-dimensional trapping structures is an important milestone for ion-trap quantum computing and quantum simulations.

Dynamical electric and magnetic metamaterial response at terahertz frequencies

Utilizing terahertz time domain spectroscopy, we characterized the electromagnetic response of planar split ring resonators fabricated on GaAs. Optical excitation is sufficient to turn off the electric resonance demonstrating the potential of SRR terahertz switches.

Integration of fluorescence collection optics with a microfabricated surface electrode ion trap

We have successfully demonstrated an integrated optical system for collecting the fluorescence from a trapped ion. The system, consisting of an array of transmissive, dielectric micro-optics and an optical fiber array, has been intimately incorporated into the ion-trapping chip without negatively impacting trapping performance. Epoxies, vacuum feedthrough, and optical component materials were carefully chosen so that they did not degrade the vacuum environment, and we have demonstrated light detection as well as ion trapping and shuttling behavior comparable to trapping chips without integrated optics, with no modification to the control voltages of the trapping chip.

Microwave conductance spectra of single-walled carbon nanotube arrays

Complex conductance spectra of single-walled carbon nanotube (SWCNT) arrays have been measured from 0.1 to 50 GHz at temperatures between 4 and 293 K. Using purely capacitive contacts to separate contact effects from the NTs’ response, the intrinsic SWCNT array conductance increased with frequency as fs with exponent s=0.67±0.08 regardless of array size and temperature. The spectra are consistent with the behavior found in many strongly inhomogeneous electronic systems. The origin of disorder in these arrays is likely topological rather than energetic.

High frequency impedance spectroscopy on ZnO nanorod arrays

The radio-frequency (rf)-to-microwave impedance spectra of solution grown ZnO nanorods have been measured from 0.1 to 50 GHz using vector network analysis. To increase interaction with rf/microwave fields, the nanorods were assembled by dielectrophoresis into arrays on coplanar waveguides. The average complex impedance frequency response per nanorod in an array was accurately modeled as a simple three-element circuit composed of the inherent nanorod resistance in series with a parallel resistor-capacitor representing the contact. The nanorod resistance dominates at high frequencies while the contact impedance dominates at low frequencies, permitting a quantitative separation of contact effects from nanorod properties. The average inherent resistivity of a nanorod was found to be ∼10−2 Ω cm, indicating the nanorods were unintentionally highly doped. Accuracy of the inherent resistance measurement was limited by the highly conductive nature of the nanorods used and the upper limit of the experimental freque...

Metamaterials for Novel Terahertz and Millimeter Wave Devices

We present experimental results of metamaterials operating at terahertz and mm-wave frequencies. Metamaterials consist of a single layer of 200 nm thick gold on a doped or undoped semiconducting substrate. By optical and electronic doping of supporting semiconducting substrates we show external control of planar arrays of metamaterials, characterized with terahertz time domain spectroscopy. Both methods yield meta-material / semiconductor devices which can be utilized as switches or modulators, enabling modulation of THz transmission by 50 percent. Experiments are supported by simulations and results agree well. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum and will undoubtedly play a key role in future demonstrations of novel high-performance devices.

Properties of Novel Terahertz Electric Metamaterials

Planar electric metamaterials are studied with terahertz time-domain spectroscopy in transmission and reflection. Energy absorption of 5-20% due to Ohmic losses within the metal patterning is observed at resonant frequencies. Finite-element simulations verify experimental results.

Terahertz metamaterials for active, tunable, and dynamic devices

Tunable electromagnetic metamaterials can be designed through the incorporation of semiconducting materials. We present theory, simulation, and experimental results of metamaterials operating at terahertz frequencies. Specific emphasis is placed on the demonstration of external control of planar arrays of metamaterials patterned on semiconducting substrates with terahertz time domain spectroscopy used to characterize device performance. Dynamical control is achieved via photoexcitation of free carriers in the substrate. Active control is achieved by creating a Schottkey diode, which enables modulation of THz Transmission by 50 percent, an order of magnitude improvement over existing devices. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum and will undoubtedly play a key role in future demonstrations of novel high-performance devices.

Dynamical Metamaterials at Terahertz Frequencies

Utilizing terahertz time domain spectroscopy, we characterized the electromagnetic response of planar Split Ring Resonators fabricated on GaAs. Optical excitation is sufficient to turn off the electric resonance demonstrating the potential of SRR terahertz switches. Other aspects of active control of metamaterials will also be discussed