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We investigate anomalous ion-motional heating, a limitation to multi-qubit quantum-logic gate fidelity in trapped-ion systems, as a function of ion-electrode separation. Using a multi-zone surfaceelectrode 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 application of noise to the electrodes, we rule out technical limitations to the measured heating rates and scalings. We also measure 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.

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 88 Sr + 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.

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 iontrap that incorporates monolithically-integrated high-voltage CMOS electronics (±8 V 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 we observe using external control elements. II. HIGH-VOLTAGE DIGITAL-TO-ANALOG CONVERTER DESIGNVoltages are derived from an R-2R resistor ladder digital-to-analog converter (DAC) [16] with 12-bits of resolution and an output range of approximately ±8 V (see Fig. 1). The DAC accepts a 12-bit code word that it translates to an analog voltage on its output (see example data in Fig. 1e). We program the DACs using an integrated serial peripheral interface (SPI) bus, controlled by arXiv:1810.07152v1 [quant-ph]

No abstract

We demonstrate key multi-qubit quantum logic primitives in a dual-species trapped-ion system based on 40 Ca + and 88 Sr + ions, using two optical qubits with quantum-logic-control frequencies in the red to near-infrared range. With all ionization, cooling, and control wavelengths in a wavelength band similar for the two species and centered in the visible, and with a favorable mass ratio for sympathetic cooling, this pair is a promising candidate for scalable quantum information processing. Same-species and dual-species two-qubit gates, based on the Mølmer-Sørensen interaction and performed in a cryogenic surface-electrode trap, are characterized via the fidelity of generated entangled states; we achieve fidelities of 98.8(2)% and 97.5(2)% in Ca + -Ca + and Sr + -Sr + gates, respectively. For a similar Ca + -Sr + gate, we achieve a fidelity of 94.3(3)%, and carrying out a Sr + -Sr + gate performed with a Ca + sympathetic cooling ion in a Sr + -Ca + -Sr + crystal configuration, we achieve a fidelity of 95.7(3)%. These primitives form a set of trapped-ion capabilities for logic with sympathetic cooling and ancilla readout or state transfer for general quantum computing and communication applications.

Microfabricated Paul ion traps show tremendous promise for large-scale quantum information processing. However, motional heating of ions can have a detrimental effect on the fidelity of quantum logic operations in miniaturized, scalable designs. In many experiments, contributions to ion heating due to technical voltage noise present on the static (DC) and radio frequency (RF) electrodes can be overlooked. We present a reliable method for determining the extent to which motional heating is dominated by residual voltage noise on the DC or RF electrodes. Also, we demonstrate that stray DC electric fields can shift the ion position such that technical noise on the RF electrode can significantly contribute to the motional heating rate. After minimizing the pseudopotential gradient experienced by the ion induced by stray DC electric fields, the motional heating due to RF technical noise can be significantly reduced.

We report and demonstrate a method for measuring the branching ratios of dipole transitions of trapped atomic ions by performing nested sequences of population inversions. This scheme is broadly applicable to species with metastable lambda systems and can be generalized to find the branching of any state to lowest states. It does not use ultrafast pulsed or narrow linewidth lasers and is insensitive to experimental variables such as laser and magnetic field noise as well as ion heating. To demonstrate its effectiveness, we make the most accurate measurements thus far of the branching ratios of both P 5 1 2 and P 5 3 2 states in 88 Sr + with sub-1% uncertainties. We measure 17.175(27) for the P 5 1 2 -S 5 1 2 branching ratio, 15.845(71) for P 5 3 2 -S 5 1 2 , and 0.056 09(21) for P 5 3 2 -D 4 5 2 . These values represent the first precision measurement for P 5 3 2 -D 4 5 2 , as well as ten-and thirty-fold improvements in precision respectively for P 5 1 2 -S 5 1 2 and P 5 3 2 -S 5 1 2 over the best previous experimental values.