Ruth Shewmon

Temperature Dependence of Electric Field Noise Above Gold Surfaces

Electric field noise from fluctuating patch potentials is a significant problem for a broad range of precision experiments, including trapped ion quantum computation and single spin detection. Recent results demonstrated strong suppression of this noise by cryogenic cooling, suggesting an underlying thermal process. We present measurements characterizing the temperature and frequency dependence of the noise from 7 to 100 K, using a single Sr+ ion trapped 75 mum above the surface of a gold plated surface electrode ion trap. The noise amplitude is observed to have an approximate 1/f spectrum around 1 MHz, and grows rapidly with temperature as T;{beta} for beta from 2 to 4. The data are consistent with microfabricated cantilever measurements of noncontact friction but do not extrapolate to the dc measurements with neutral atoms or contact potential probes.

Individual addressing of ions using magnetic field gradients in a surface-electrode ion trap

A dense array of ions in microfabricated traps represents one possible way to scale up ion trap quantum computing. The ability to address individual ions is an important component of such a scheme. We demonstrate individual addressing of trapped ions in a microfabricated surface-electrode trap using a magnetic field gradient generated on-chip. A frequency splitting of 310(2) kHz for two ions separated by 5 μm is achieved. Selective single qubit operations are performed on one of two trapped ions with an average of 2.2(±1.0%) crosstalk. Coherence time is reduced by the magnetic field gradient, but the spin-echo technique effectively restores the coherence time.

Demonstration of a quantum logic gate in a cryogenic surface-electrode ion trap

We demonstrate quantum control techniques for a single trapped ion in a cryogenic, surface-electrode trap. A narrow optical transition of Sr{sup +} along with the ground and first excited motional states of the harmonic trapping potential form a two-qubit system. The optical qubit transition is susceptible to magnetic field fluctuations, which we stabilize with a simple and compact method using superconducting rings. Decoherence of the motional qubit is suppressed by the cryogenic environment. ac Stark shift correction is accomplished by controlling the laser phase in the pulse sequencer, eliminating the need for an additional laser. Quantum process tomography is implemented on atomic and motional states by use of conditional pulse sequences. With these techniques, we demonstrate a Cirac-Zoller controlled-not gate in a single ion with a mean fidelity of 91(1)%.

Compact, Ti:sapphire-based, methane-stabilized optical molecular frequency comb and clock

A compact optical clock and frequency comb system is presented, based on a 1 GHz octave-spanning Ti:sapphire laser referenced to the F2(2)(P(7),v3) optical transition in methane at 3.39 microm. The reference methane transition is accessed by a stabilized HeNe laser in a compact transportable format. The output from the octave-spanning Ti:sapphire laser is used to generate a mid-IR comb at the reference wavelength 3.39 microm. Direct comparison of the stabilized optical frequency comb with an ultralow expansion glass cavity-stabilized diode laser at 674 nm shows an Allan deviation of the frequency comb of 3x10(-14) in 20 s.