November_EDFA_Digital 29 ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 4 excite the ion out of the desired state or to reorder ions in a chain (logical qubit) and scramble any encoded infor- mation. Thus, the desired vacuum pressure is the lowest possible, typically around 10 −12 Torr, near-XHV (extreme high vacuum). These ultra-low pressures are realized by baking the entire chamber at 200°C, ideally for as long as possible, but 1-2weeks is typical and this extreme temper- ature creates special requirements for ion trap chips. The vacuumrequirements of trapped ions are a key difference in the quantumplatforms; for example, superconducting qubits require sub-milliKelvin cryogenic temperatures to keep the background energy level small and a vacuum to prevent ice, but not ultrahigh vacuum (UHV). Although ion traps can operate at room temperature they are often operated at cryogenic conditions (albeit at more moderate temperatures of about 5 K) with every- thing inside the vacuum chamber attached to a cryostat cold finger. In this regime, most background gases are frozen out and the remainder have a low enough colli- sional energy that the probability of ion chain reordering is low. Each environment has advantages anddisadvantages making them equally common approaches for trapped ion experiments and thus any ion trap device may either be baked or frozen. Microfabricated-surface ion traps have many advan- tages over 3D ion trap designs and are widely regarded as a solution to the scaling problem in trapped ions. [6] A description of how surface traps compare to 3D traps can be found in Seidelin, et al. [7] The surface traps use long RF rails surrounded by control (nominally static voltage) electrodes (shown in the inset of Fig. 2) to create Fig. 1 (a) An example of an ion trapping experiment in situ. (b) Image through one of the 4.5 in. viewports on the chamber. All the lasers are precisely aligned to the center of the trapping device, each comes to a focus of 5-50 µm. Inside the chamber, the trap is held upside down to reduce the risk of dust collecting on the surface. To change the trap, the entire chamber is removed from the optical table and vented to atmosphere through a small orifice (also to reduce dust kick-up). The new device is typically installed in a clean room. (a) (b) Fig. 2 Optical image of the Phoenix surface trap. The inset shows a zoomed in optical picture of the surface electrodes at the center of the trap. The large electrodes on the top and bottom are the outer segmented electrodes or compensation electrodes, eachhas awidthof 140µm. TheRF rails arehorizontal and inside the outer electrodes on the top and bottom. The inner segmented electrodes allow for precise position control of a chain of ions. The black region in the middle of the device is a through-chip slot in the trap to allow lasers or atoms to pass through the substrate. (continued on page 32)