AbstractWe demonstrate key multi-qubit quantum-logic primitives in a dual-species trapped-ion system based on $${}^{40}$$40Ca$${}^{+}$$+ and $${}^{88}$$88Sr$${}^{+}$$+ ions, using two optical qubits with quantum-logic-control frequencies in the red to near-infrared range. With all ionization, cooling, and control wavelengths in a wavelength band similar for the two species and centered in the visible, and with a favorable mass ratio for sympathetic cooling, this pair is a promising candidate for scalable quantum information processing. Same-species and dual-species two-qubit gates, based on the Mølmer–Sørensen interaction and performed in a cryogenic surface-electrode trap, are characterized via the fidelity of generated entangled states; we achieve fidelities of 98.8(2)% and 97.5(2)% in Ca$${}^{+}$$+–Ca$${}^{+}$$+ and Sr$${}^{+}$$+–Sr$${}^{+}$$+ gates, respectively. For a similar Ca$${}^{+}$$+–Sr$${}^{+}$$+ gate, we achieve a fidelity of 94.3(3)%, and carrying out a Sr$${}^{+}$$+–Sr$${}^{+}$$+ gate performed with a Ca$${}^{+}$$+ sympathetic cooling ion in a Sr$${}^{+}$$+–Ca$${}^{+}$$+–Sr$${}^{+}$$+ crystal configuration, we achieve a fidelity of 95.7(3)%. These primitives form a set of trapped-ion capabilities for logic with sympathetic cooling and ancilla readout or state transfer for general quantum computing and communication applications.
Character of motional modes for entanglement and sympathetic cooling of mixed-species trapped-ion chains
