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arXiv:2211.07121 · Physical Review A

Surface trap with adjustable ion couplings for scalable and parallel gates

Yelnury Suleimen, A. Podlesnyy, L. A. Akopyan, N. Sterligov, Olga Lakhmanskaya, Evgeny V. Anikin, Arthur Matveev, Kirill Lakhmanskiy

Published Feb 9, 2024• 3 citations
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Abstract

We describe the design and operation of a surface-electrode Paul trap for parallel entangling gate implementation. In particular, we demonstrate the possibility of separating or coupling ion motion by adjusting the DC-voltages on a set of electrodes and show the possibility of parallel MS-gate operations for specific voltage configurations. We verify the scalability of this approach and characterize the performance of these gates in the presence of the finite phonon mode occupation and of the finite drift of the phonon frequencies. Additionally, we investigate how the number of ions per individual trapping site and anharmonic potential terms affect the coupling between the wells.

DOI
10.1103/physreva.109.022605

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We describe the design and operation of a surface-electrode Paul trap for parallel entangling gate implementation. In particular, we demonstrate the possibility of separating or coupling ion motion by adjusting the DC-voltages on a set of electrodes and show the possibility of parallel MS-gate operations for specific voltage configurations. We verify the scalability of this approach and characterize the performance of these gates in the presence of the finite phonon mode occupation and of the finite drift of the phonon frequencies. Additionally, we investigate how the number of ions per individual trapping site and anharmonic potential terms affect the coupling between the wells.
We present a surface-electrode Paul trap featuring integrated photonics elements, where ions are illuminated with two interfering beams at 729 nm forming a standing wave along the trap axis. In this field configuration, it is possible to excite the motional sidebands of a trapped ion while suppressing the off- resonant coupling to the corresponding carrier transition. This is of particular interest for quantum information processing, as it would allow implementing faster and lower error Mølmer-Sørensen entangling gates.We characterize the optical properties of the chip by scanning with sub-wavelength resolution the position of a single ion through the standing wave and observing Rabi oscillations for carrier and first motional sideband of different quadrupole transitions. We characterize both the strength of resonant couplings and the AC Stark shift induced by off-resonant couplings. We measure noise and drifts in the ion position and observe high stability in the standing wave profile without the need for active phase stabilization.Integrated optics allow to reliably reproduce the same field configuration in different regions of the chip, opening the way for implementing distributed, parallel quantum operations. We show the ability to control ions in different regions of the trap at the same time. We implemented real-time control of the DC voltages controlling the axial configuration of the trapping potential which enables us to load multiple ion crystals, merge, split, and shuttle them across the device.
We describe the design, fabrication, and operation of a novel surface-electrode Paul trap that produces a radio-frequency-null along the axis perpendicular to the trap surface. This arrangement enables control of the vertical trapping potential and consequentially the ion-electrode distance via dc-electrodes only. We demonstrate the confinement of single 40Ca+ ions at heights between 50 μm and 300 μm above planar copper-coated aluminum electrodes. Laser-cooling and coherent operations are performed on both the planar and vertical motional modes. This architecture provides a platform for precision electric-field noise detection and trapping of vertical ion strings without excess micromotion and may have applications for scalable quantum computers with surface ion traps.
Trapped-ion quantum computers have demonstrated high-performance gate operations in registers of about ten qubits. However, scaling up and parallelizing quantum computations with long 1D ion strings is an outstanding challenge due to the global nature of the motional modes of the ions which mediate qubit-qubit couplings. We devise methods to implement scalable and parallel entangling gates by using engineered localized phonon modes. We propose to tailor these modes by tuning the local potential of individual ions with programmable optical tweezers. Localized modes of small subsets of qubits enable to perform entangling gates on these subsets in parallel.
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Ion trap is one of the most promising candidates for quantum computing. High-fidelity gates have been demonstrated in small ion crystals and schemes like ion shuttling have been proposed for larger systems. This thesis discusses the possibility of direct quantum computing on a large ion crystal in a Paul trap, without any shuttling of the ions. We first review a scheme to entangle two ions in a small ion crystal mediated by the collective phonon modes and analyze the gate errors. The generalization to larger systems is divided into three parts. (1) We present numerical methods to solve all the normal modes of the ion crystal, including the micromotion, up to arbitrary precision. The stability of the crystal under infinitesimal perturbation is ensured when all the normal modes have real frequencies. For finite disturbance, direct molecular dynamics simulation will be needed; after discussing some potential problems in the simulation, we give a rule of thumb for the ion crystal to be stable at a given temperature. (2) We show that when designing an entangling gate between two nearby ions, all the ions far away can be neglected, so that only a small number of normal modes are relevant. Similarly, distant entangling gates can be applied in parallel and the crosstalk is shown to decay cubically with the distance between these gates. (3) Then we present numerical methods to include the solved micromotion into the design of the entangling gates efficiently, again up to arbitrary precision. Thus we conclude that the design and the implementing of entangling gates are scalable in a large ion crystal. Finally we consider a near-term application to simulate an all-to-all coupled Ising model in a small to medium-sized ion crystal.
We report a linear surface-electrode trap that can be used to form parallel ion strings. By adjusting the balance of the radio-frequency (RF) voltages applied to central and RF electrodes, the RF pseudopotential can be varied from single-well to double-well in the radial direction. Ions located on two parallel lines of the RF potential null are in principle free from excess micromotion if appropriate static voltages are applied. Calcium ions were trapped for the evaluation of the designed electrode. An ion string in the single-well potential and two ion strings in the double-well potential were observed by changing the RF voltages. Such traps could be used for quantum simulation of coupled spin systems.