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The existing bottleneck in efficiently miniaturizing components for quantum computers could be eased with the help of 3D printing.

Quantum computers tackle massive computational challenges by harnessing the power of countless tiny parts working seamlessly together. Trapped ion technology, where charged particles like ions are trapped by manipulating the electromagnetic fields, is one such component.

Current microfabrication techniques fall short when it comes to producing the complex electrode structures with optimal ion confinement suitable for quantum operations.

Researchers have found a solution to this problem in high-resolution 3D printing. In a published in Nature, scientists from the University of California and Lawrence Berkeley National Laboratory showed that two-photon polymerization (2PP), a popular name in the world of microscale 3D printing, can fabricate large arrays of miniaturized 3D ion traps with complex geometries, without sacrificing scalability or precision.

A quantum computer needs a way to store quantum information, and individual ions confined in trapped-ion systems fulfill this role by acting as qubits—the fundamental carriers of quantum information.

To make this possible, ion traps use electric fields to hold the ions in a deep potential well, which prevents them from drifting away or being disturbed by their surroundings.

Traditional 3D ion traps use electrodes arranged around the ion in three dimensions, which offers strong confinement but doesn't miniaturize well.

Furthermore, the large ion-electrode distance (≈1 mm) weakens the electric field strength produced for a given voltage. Weaker fields equals lower trap frequency, which is the measure of how tightly an ion can be held in place. This makes them unsuitable for scalable quantum computing.

Studies have explored surface traps built from 2D electrode structures created via photolithography techniques—a process in semiconductor manufacturing that applies a light-sensitive material to create precise patterns—to miniaturize traps. These structures, however, require the ions to be stored very close to the electrodes to keep them in place. This often results in electric field noise from the electrodes generating heat, which can lead to errors in quantum operations.

To overcome these issues, the researchers presented a high-resolution 3D printing method for building traps that combined the benefits of traditional machined 3D traps, such as strong radial confinement, with the miniaturization and scalability of chip-based devices.

They built ion traps directly on sapphire substrates using Nanoscribe, a commercially available 3D printer that operates on two-photon polymerization, where highly focused lasers solidify a liquid resin to form precise three-dimensional structures. These traps were then metal-coated with either gold or aluminum.

Using these traps, the team successfully confined calcium ions with radial trap frequencies between 2 and 24 MHz. They also demonstrated high-fidelity quantum operations, such as a two-qubit gate with a Bell-state fidelity of 0.978 ± 0.012, which further established the reliability of the designed traps in supporting quantum computing.

The researchers noted that 3D ion traps designed using the proposed method achieved trap frequencies that were four times higher than those typically seen in both macro 3D traps and surface traps.

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