Single-ion addressing via trap potential modulation in global optical fields

Abstract

To date, individual addressing of ion qubits has relied primarily on local Rabi or transition frequency differences between ions created via electromagnetic field spatial gradients or via ion transport operations. Alternatively, it is possible to synthesize arbitrary local one-qubit gates by leveraging local phase differences in a global driving field. Here we report individual addressing of 40 Ca + ions in a two-ion crystal using axial potential modulation in a global gate laser field. We characterize the resulting gate performance via one-qubit randomized benchmarking, applying different random sequences to each co-trapped ion. We identify the primary error sources and compare the results with single-ion experiments to better understand our experimental limitations. These experiments form a foundation for the universal control of two ions, confined in the same potential well, with a single gate laser beam.

Quantum process tomography of a Mølmer-Sørensen gate via a global beam

“…For these experiments, two 40 Ca + ions are confined with a surface-electrode linear Paul trap [16,25]. Radial confinement is provided by an RF potential at 56.4 MHz (peak voltage ≈ 176 V) that traps the ions 58 µm above the trap surface.…”

“…We realize individually addressed one-qubit rotations through composite sequences of 729 nm laser pulses and modulations to the confining potential as described in [16]. Here we use two laser pulses and two potential modulations to produce one-qubit rotations on a single ion in 15 µs.…”

“…To produce high-fidelity single-ion rotations for qubit state initialization and measurement during the QPT experiments, we sought to reduce the axial mode heating previously observed in randomized benchmarking experiments of the potential modulation single-ion addressing technique [16]. For that work, the trap electrode voltages were provided by National Instruments 16-bit PXI-6733 digital-to-analog converter (DAC) cards in a PXI-1045 chassis.…”

“…In this paper, we present a framework for performing QPT on two co-trapped ions that alleviates the time, ion-transport, and hardware constraints of other techniques. We achieve single-ion addressing through a method involving modulations of the ions' confining potential, as previously demonstrated by Seck et al [16], but improved here to reduce the impact on ion temperatures. Section 2 provides a brief summary of the mathematical formulation of QPT and of the challenges of performing QPT with trapped-ion chains.…”

Quantum process tomography of a Mølmer-Sørensen gate via a global beam

“…In this paper, we present a framework for performing QPT on two co-trapped ions that alleviates the time, ion-transport, and hardware constraints of other techniques. We achieve single-ion addressing through a method involving modulations of the ions' confining potential, as previously demonstrated by Seck et al [17], but improved here to reduce the impact on ion temperatures. Section 2 provides a brief summary of the mathematical formulation of QPT and of the challenges of performing QPT with trapped-ion chains.…”