High-Fidelity Quantum Logic in Ca+

Marius Weber, Clemens Löschnauer, Jochen B. W. Wolf +6 more

Colin Bruzewicz, Robert McConnell, Jules Stuart +2 more

Abstract We demonstrate key multi-qubit quantum-logic primitives in a dual-species trapped-ion system based on $${}^{40}$$ 40 Ca $${}^{+}$$ + and $${}^{88}$$ 88 Sr $${}^{+}$$ + 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 $${}^{+}$$

David Finkelstein

Xingyu Zhao, Ji Bian, Yi Li +3 more

Abstract Trapped-ion systems are one of the leading platforms for quantum information processing, where a key challenge is to scale up system size while maintaining high-fidelity two-qubit operations. A promising approach is to build high-performance modules interconnected via strong coupling. In particular, axial motional modes offer a practical mechanism to couple the ions in a chain, enabling the preparation of Greenberger–Horne–Zeilinger states with up to 24 ions using global operations, as well as high-fidelity two-qubit gates (96.6%–98.0%) in fully connected five-ion chains. Here, we demonstrate two-qubit quantum logic gates in a 5-ion 40 Ca + chain using axial modes, achieving fidelities exceeding 99% for adjacent pairs and over 98% for arbitrary pairs by carefully tackling dominant error sources. Our results are beneficial to the development of scalable ion-trap quantum processors, quantum simulation and quantum-enhanced metrology.

María Luisa Dalla Chiara, Roberto Giuntini, Roberto Leporini +1 more

T. P. Harty, M. A. Sepiol, D. T. C. Allcock +3 more

We demonstrate a two-qubit logic gate driven by near-field microwaves in a room-temperature microfabricated surface ion trap. We introduce a dynamically decoupled gate method, which stabilizes the qubits against fluctuating energy shifts and avoids the need to null the microwave field. We use the gate to produce a Bell state with fidelity 99.7(1)%, after accounting for state preparation and measurement errors. The gate is applied directly to ^{43}Ca^{+} hyperfine "atomic clock" qubits (coherence time T_{2}^{*}≈50 s) using the oscillating magnetic field gradient produced by an integrated microwave electrode.