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Conference on Lasers and Electro-Optics

Repeated Multi-Qubit Readout and Feedback in a Mixed-Species Trapped-Ion Register

Karan K. Mehta, Vlad Negnevitsky, Matteo Marinelli, Hsiang-Yu Lo, Christa Flühmann, Jonathan Home

Published Jan 1, 2019• 10 citations
Publisher

Abstract

We measure the parity of two 9Be+ion qubits by mapping the relevant operator onto an ancillary 40Ca+qubit, utilizing multi-species entangling gates. Repeated measurement and feedback cycles allow preparation and stabilization of parity subspaces and Bell states.
DOI
10.1364/cleo_qels.2019.fth3a.1

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Abstract Fault-tolerant quantum computing relies on the ability to detect and correct errors, which in quantum error correction codes is typically achieved by projectively measuring multi-qubit parity operators and by conditioning operations on the observed error syndromes. Here, we experimentally demonstrate the use of an ancillary qubit to repeatedly measure the ZZ and XX parity operators of two data qubits and to thereby project their joint state into the respective parity subspaces. By applying feedback operations conditioned on the outcomes of individual parity measurements, we demonstrate the real-time stabilization of a Bell state with a fidelity of F ≈ 74% in up to 12 cycles of the feedback loop. We also perform the protocol using Pauli frame updating and, in contrast to the case of real-time stabilization, observe a steady decrease in fidelity from cycle to cycle. The ability to stabilize parity over multiple feedback rounds with no further reduction in fidelity provides strong evidence for the feasibility of executing stabilizer codes on timescales much longer than the intrinsic coherence times of the constituent qubits.
Large-scale quantum information processors must be able to transport and maintain quantum information and repeatedly perform logical operations. Here, we show a combination of all of the fundamental elements required to perform scalable quantum computing through the use of qubits stored in the internal states of trapped atomic ions. We quantified the repeatability of a multiple-qubit operation and observed no loss of performance despite qubit transport over macroscopic distances. Key to these results is the use of different pairs of 9Be+ hyperfine states for robust qubit storage, readout, and gates, and simultaneous trapping of 24Mg+ "re-cooling" ions along with the qubit ions.
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