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arXiv:2404.02105 · Physical Review Letters

Individual-Ion Addressing and Readout in a Penning Trap

Brian J. McMahon, Kenton R. Brown, Creston D. Herold, Brian C. Sawyer

Published Oct 23, 2024• 11 citations
arXivHTMLPDF

Abstract

We implement individual addressing and readout of ions in a rigidly rotating planar crystal in a compact, permanent magnet Penning trap. The crystal of ^{40}Ca^{+} is trapped and stabilized without defects via a rotating triangular potential. The trapped ion fluorescence is detected in the rotating frame for parallel readout. The qubit is encoded in the metastable D_{5/2} manifold enabling the use of high-power near-infrared laser systems for qubit operations. Addressed σ_{z} operations are realized with a focused ac Stark shifting laser beam. We demonstrate addressing of ions near the center of the crystal and at large radii. Simulations show that the current addressing operation fidelity is limited to ∼97% by the ion's thermal extent for the in-plane modes near the Doppler limit, but this could be improved to infidelities <10^{-3} with sub-Doppler cooling. The techniques demonstrated in this Letter complete the set of operations for quantum simulation with the platform.

DOI
10.1103/physrevlett.133.173201

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•Jan 1, 2019•1 citation
We implement individual addressing and readout of ions in a rigidly rotating planar crystal in a compact, permanent magnet Penning trap. The crystal of ^{40}Ca^{+} is trapped and stabilized without defects via a rotating triangular potential. The trapped ion fluorescence is detected in the rotating frame for parallel readout. The qubit is encoded in the metastable D_{5/2} manifold enabling the use of high-power near-infrared laser systems for qubit operations. Addressed σ_{z} operations are realized with a focused ac Stark shifting laser beam. We demonstrate addressing of ions near the center of the crystal and at large radii. Simulations show that the current addressing operation fidelity is limited to ∼97% by the ion's thermal extent for the in-plane modes near the Doppler limit, but this could be improved to infidelities <10^{-3} with sub-Doppler cooling. The techniques demonstrated in this Letter complete the set of operations for quantum simulation with the platform.
Trapped ions boast long coherence times and excellent gate fidelities, making them a useful platform for quantum information processing. Penning traps offer the possibility of trapping large two-dimensional crystals of several hundred ions. The ions are confined by controlling the rotation of the ion crystal in the presence of a strong magnetic field. However, the rotation of the ion crystal makes single ion addressability a significant challenge. We propose a protocol that takes advantage of a deformable mirror to introduce AC Stark shift patterns that are static in the rotating frame of the crystal. Through numerical simulations we validate the potential of this protocol to perform high-fidelity single-ion gates in crystalline arrays of hundreds of ions.
Large ion crystals in Penning traps provide a platform for quantum simulation and sensing with hundreds of spins, but their continuous rigid-body rotation has so far limited flexible local qubit control. Here we demonstrate programmable coherent site-selective spin control across large rotating 9Be+{}^{9}\mathrm{Be}^{+}9Be+ crystals in a Penning trap. A tightly focused off-resonant laser beam drives local RzR_zRz​ phase rotations via differential AC Stark shifts. Beam steering synchronised with crystal rotation enables addressing of arbitrary ions throughout the crystal. Ramsey-based characterisation shows Rz(π)R_z(π)Rz​(π) gate fidelity of 0.950(4) and nearest-neighbour crosstalk error of 0.021(6). We demonstrate preparing spatially structured spin patterns, generating a biskyrmion spin texture in a single-layer crystal, and then extend the method to bilayer crystals where we perform layer-selective addressing operations. We further demonstrate dual-quadrature Ramsey sensing by imprinting a relative π/2π/2π/2 phase shift between spatial sub-ensembles, enabling simultaneous measurement of orthogonal spin components within a single experimental realisation. These results establish programmable local control in large rotating ion crystals, opening new routes for engineering spatially structured quantum states in multidimensional trapped-ion systems.
Trapped ions boast long coherence times and excellent gate fidelities, making them a useful platform for quantum information processing. Scaling to larger numbers of ion qubits in RF Paul traps demands great effort. Another technique for trapping ions is via a Penning trap where a 2D crystal of hundreds of ions is formed by controlling the rotation of the ions in the presence of a strong magnetic field. However, the rotation of the ion crystal makes single ion addressability a significant challenge. We propose a protocol that takes advantage of a deformable mirror to introduce AC Stark shift patterns that are static in the rotating frame of the crystal. Through numerical simulations we validate the potential of this protocol to perform high-fidelity single-ion gates in crystalline arrays of hundreds of ions.
Penning ion traps as quantum platforms have primarily utilized global control and symmetric Dicke states for quantum simulation and sensing experiments. The introduction of local control greatly increases the power of the platform as a quantum simulator but is technically challenging due to the rapid rotation of the ion crystals. Here we use an ultraviolet-compatible spatial light modulator (SLM) to imprint programmable AC Stark shift patterns with different azimuthal symmetries and gradients that co-rotate with the ion crystals, demonstrating localized coherent control of single plane crystals with greater than 100 ions. Comparisons of the measured ion qubit populations with calculations from independent measurements of the applied AC Stark shift patterns show good agreement, validating the technique and providing a path, with a higher format SLM, for parallelizable, coherent individual ion addressing in Penning traps.
Large, 3D trapped ion crystals offer improved sensitivity in quantum sensing protocols, and are expected to be implemented as platforms in near-future experiments. However, numerical techniques used to study the laser cooling of such crystals are inefficient as the number of ions, NNN, in the crystal increases. Here we develop a powerful numerical framework to simulate laser cooling of up to 10510^5105 ions stored in a Penning trap. We apply this framework to characterize and optimize the cooling of ellipsoidal 3D crystals. We document new pathways to enhanced cooling based on the addition of an axial component to the potential energy-dominated E×B\boldsymbol{E}\times\boldsymbol{B}E×B modes. Furthermore, we observe greatly enhanced cooling of the perpendicular kinetic energy to below 1 mK in prolate ion crystals, enabling a simplified cooling beam setup for such crystals. We propose specific values of trap and laser beam parameters which lead to optimal cooling in a variety of examples. This work illustrates the feasibility of preparing large 3D crystals for high-sensitivity quantum science protocols, motivating their use in future experiments.
In the search for new computational paradigms past the impending end of Moore’s law quantum information processing based on cold trapped ions has emerged as a promising candidate. This thesis presents on the design, construction and testing of a setup for analog quantum simulation experiments using Be ion crystals in a Penning trap. At the heart of the experiment is a specialized Penning trap with wide optical access for engineering Ising-type interactions. The trap sits inside a superconducting magnet which runs continuously with minimal losses through a novel dual-stage reliquefier system. During this thesis, mechanical and optical subsystems for this ion trap quantum simulator were designed and built. Two laser systems based on nonlinear frequency conversion were set up to generate light for photoionization, Doppler cooling, state preparation, readout, and Raman interactions. In parallel, a method was devised to produce ultraviolet-solarization resistant fiber patch cords for pointing-stable light delivery. Inbore optomechanics and a collaboratively designed precision six-axis positioning device were constructed for beam delivery and trap alignment, respectively. These optomechanics co-locate custom-designed millimeterwave delivery systems as well as numerically optimized, diffraction-limited imaging optics for fluorescence readout. Using these subsystems, we validate interferometrically the motional stability of the setup from the mHz to kHz region during pulse-tube operation. First-ever light-ion interaction serves to validate calculations of interaction frequencies, optomechanics operation, and imaging performance, while coherent qubit interaction allows for this to be done on the millimeter wave setup, where initial Rabi flopping times of 18 us were observed. Site-resolved imaging of rapidly rotating ion crystals demonstrates critical phase-locked operation of the apparatus; positioning the experiment for future upgrades towards a full analog quantum simulator.