We demonstrate a quantum processor based on a 3D linear Paul trap that uses ${}^{171}\mathrm{Yb}^{+}$ ions with eight individually controllable four-level qudits (ququarts), which is computationally equivalent to a sixteen-qubit quantum processor. The design of the developed ion trap provides high secular frequencies and a low heating rate, which, together with individual addressing and readout optical systems, allows executing quantum algorithms. In each of the eight ions, we use four electronic levels coupled by E2 optical transition at 435 nm for qudit encoding. We present the results of single- and two-qubit operations benchmarking and realizing basic quantum algorithms, including the Bernstein–Vazirani and Grover’s search algorithms as well as H₂ and LiH molecular simulations. Our results pave the way to scalable qudit-based quantum processors using trapped ions.

An efficient implementation of the Toffoli gate is of conceptual importance for running various quantum algorithms, including Grover's search and Shor's integer factorization. However, direct implementation of the Toffoli gate either entails a prohibitive increase in the number of two-qubit gates or requires ancilla qubits, whereas both of these resources are limited in the current generation of noisy intermediate-scale quantum devices. Here, we experimentally demonstrate a scalable N-qubit Toffoli gate improvement using ^{171}Yb^{+} trapped-ion-based optical-metastable-ground encoded qutrits for the cases of up to N=10. With the use of the Mølmer-Sørensen gate as a basic entangling operation, we compare the standard qubit decomposition with the qutrit approach, where upper levels are used as ancillae. The presented decomposition requires only global control of the ancilla levels, which simplifies experimental implementation of the proposed approach. Using the example of a three-qubit Grover's search, we also demonstrate an increase in the algorithm's accuracy by monitoring the leakage from the qubit subspace during a qutrit-based Toffoli gate implementation.

We demonstrate a simple nonisotope-selective method for ion trap loading, which is based on the irradiation of trap electrodes precoated with materials with a low work function by a light-emitting diode (LED). Photoelectrons emitted from the electrode surface and accelerated in the trap electric field ionize the atomic beam inside the trap, which results in the trap loading. We studied Y₂O₃ and Mg coatings for the trap electrodes and experimentally demonstrated trapping of single ²⁴Mg⁺ ions as well as large ion crystals composed of up to 10³ particles using a 400 nm LED. This method can be readily implemented in a variety of applications where simplicity, compactness, and robustness are critical, such as in portable ion frequency standards and commercial ion-based devices, for example. Possible modifications of this technique aimed for selective loading, reduction of induced electric stray fields, and getting rid of atomic oven are also discussed.