MICROWAVE AND SURFACE ELECTROMETRY WITH RYDBERG ATOMS

Measurements of microwave electric fields in rubidium vapor cells, and of static electric fields near quartz with cold rubidium are presented. The measurements are performed using electromagnetically induced transparency (EIT) with Rydberg atoms. The theoretical basics of Rydberg atoms and EIT are discussed. An electric field perturbs the energy levels of Rydberg states, and Rydberg atom EIT is used to measure the perturbation. Experimental and theoretical results are presented, demonstrating the ability to measure the amplitude and polarization of microwave electric fields. These measurements are done using room temperature vapor cells, providing a pathway for portable atom based sensing of microwave electric fields. A second set of experiments is done with cold rubidium atoms in a magnetic trap near the (0001) surface of single crystal quartz. The experimental apparatus and lasers used in the experiments are described in detail. Electric fields due to Rb adsorbates on the surface are measured. The thermal desorption of Rb from the surface is characterized and theoretically analyzed using a Langmuir isobar. Blackbody ionization of Rydberg atoms produces electrons with low kinetic energy. The blackbody electrons bind to the surface and reduce the overall electric field. Electric fields as small as 30 mV/cm have been measured 20 µm from the surface. These results open up possibilities for using Rydberg atoms in hybrid quantum systems. Some of these possibilities are discussed

Evidence for multiple mechanisms underlying surface electric-field noise in ion traps

Electric-field noise from ion-trap electrode surfaces can limit the fidelity of multiqubit entangling operations in trapped-ion quantum information processors and can give rise to systematic errors in trapped-ion optical clocks. The underlying mechanism for this noise is unknown, but it has been shown that the noise amplitude can be reduced by energetic ion bombardment, or “ion milling,” of the trap electrode surfaces. Using a single trapped ⁸⁸Sr⁺ ion as a sensor, we investigate the temperature dependence of this noise both before and after ex situ ion milling of the trap electrodes. Making measurements over a trap electrode temperature range of 4 K to 295 K in both sputtered niobium and electroplated gold traps, we see a marked change in the temperature scaling of the electric-field noise after ion milling: power-law behavior in untreated surfaces is transformed to Arrhenius behavior after treatment. The temperature scaling becomes material-dependent after treatment as well, strongly suggesting that different noise mechanisms are at work before and after ion milling. To constrain potential noise mechanisms, we measure the frequency dependence of the electric-field noise, as well as its dependence on ion-electrode distance, for niobium traps at room temperature both before and after ion milling. These scalings are unchanged by ion milling.National Science Foundation (U.S.) (Award DMR-14-19807)United States. Air Force Office of Scientific Research (Contract FA8721-05-C-0002

Chip-Integrated Voltage Sources for Control of Trapped Ions

Trapped-ion quantum-information processors offer many advantages for achieving high-fidelity operations on a large number of qubits, but current experiments require bulky external equipment for classical and quantum control of many ions. We demonstrate the cryogenic operation of an ion trap that incorporates monolithically integrated high-voltage complementary metal-oxide semiconductor (CMOS) electronics (±8V full swing) to generate surface-electrode control potentials without the need for external analog voltage sources. A serial bus programs an array of 16 digital-to-analog converters (DACs) within a single chip that apply voltages to segmented electrodes on the chip to control ion motion. Additionally, we present the incorporation of an integrated circuit that uses an analog switch to reduce voltage noise on trap electrodes due to the integrated amplifiers by over 50 dB. We verify the function of our integrated electronics by performing diagnostics with trapped ions and find noise and speed performance similar to those that we observe using external control elements

Distance scaling of electric-field noise in a surface-electrode ion trap

We investigate anomalous ion-motional heating, a limitation to multiqubit quantum-logic gate fidelity in trapped-ion systems, as a function of ion-electrode separation. Using a multizone surface-electrode trap in which ions can be held at five discrete distances from the metal electrodes, we measure power-law dependencies of the electric-field noise experienced by the ion on the ion-electrode distance d. We find a scaling of approximately d^{−4} regardless of whether the electrodes are at room temperature or cryogenic temperature, despite the fact that the heating rates are approximately two orders of magnitude smaller in the latter case. Through auxiliary measurements using the application of noise to the electrodes, we rule out technical limitations to the measured heating rates and scalings. We also measure the frequency scaling of the inherent electric-field noise close to 1/f at both temperatures. These measurements eliminate from consideration anomalous-heating models which do not have a d⁻⁴ distance dependence, including several microscopic models of current interest