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Physical Review Letters

Qubit Syndrome Measurements with a High-Fidelity Rb-Cs Rydberg Gate

Jared A. Miles, Martin Lichtman, A. M. Scott, J. Scott, Sam A. Norrell, Matt J. Bedalov, D. A. Belknap, Daniel C. Cole, S. Y. Eubanks, M. Gillette, P. Gokhale, J. Goldwin, M. Iliev, R. A. Jones, Kevin W. Kuper, D. Mason, P. T. Mitchell, Joseph D. Murphree, Nathan A. Neff-Mallon, T. W. Noel, A. G. Radnaev, Ilya Vinogradov, Mark E. Saffman

Published Aug 3, 2026• 2 citations
Publisher

Abstract

We demonstrate an interspecies entangling Rydberg gate between rubidium (Rb) and cesium (Cs) atoms with fidelity F=0.975±0.002. The two-species atom array enables in-place quantum nondemolition (QND) qubit measurements which are a key capability for quantum error correction. We demonstrate this functionality with multiatom error syndrome measurements achieving QND measurement fidelities of F_{QND}=0.933(12) and 0.865(17) for two- and three-qubit plaquettes, respectively.

DOI
10.1103/pvjm-jxd2

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quant-pharXiv:2610.08926•Oct 8, 2026•0 citations
We demonstrate an interspecies entangling Rydberg gate between rubidium (Rb) and cesium (Cs) atoms with fidelity F=0.975±0.002. The two-species atom array enables in-place quantum nondemolition (QND) qubit measurements which are a key capability for quantum error correction. We demonstrate this functionality with multiatom error syndrome measurements achieving QND measurement fidelities of F_{QND}=0.933(12) and 0.865(17) for two- and three-qubit plaquettes, respectively.
We demonstrate an inter-species entangling Rydberg gate between rubidium (Rb) and cesium (Cs) atoms with fidelity F=0.975±0.002\mathcal F = 0.975\pm 0.002F=0.975±0.002. The two-species atom array enables in-place quantum non-demolition (QND) qubit measurements which are a key capability for quantum error correction. We demonstrate this functionality with multi-atom error syndrome measurements achieving QND measurement fidelities of FQND=0.933(12){\mathcal F}_{\rm QND} = 0.933(12)FQND​=0.933(12) and 0.865(17)0.865(17)0.865(17) for two- and three-qubit plaquettes, respectively.
We propose and analyze an approach for fast syndrome measurements in an array of rubidium and cesium atomic qubits. The scheme works by implementing an interspecies controlled-not (cnotk{}_{k}k​) gate, entangling one cesium ancilla qubit with $k\ensuremath{\ge}1$ rubidium qubits which are then used for state measurement. Utilizing Rydberg states with different interspecies and intraspecies interaction strengths, the proposal provides a syndrome measurement fidelity of F>0.9999\mathcal{F}>0.9999F>0.9999 in less than $5\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{s}$ of integration time.
The ability to locally control and measure subsets of ancilla qubits in an efficient and crosstalk-free manner is a key ingredient in quantum error correction (QEC). Dual-species neutral atom arrays offer an ideal implementation of these capabilities, enabling independent state preparation, manipulation, and detection on each species. In this work, we realize such a dual-species Rydberg array of Na and Cs atoms trapped in co-localized 2D optical tweezer arrays, using Na as an ancilla to measure stabilizers of surrounding Cs data qubits. We identify the finite interspecies Rydberg-Rydberg interaction strength as a practical obstacle to high-fidelity multi-body entanglement and show that, by tuning the Rabi frequency and the detuning of the Rydberg driving field, the resulting geometric phase error can be compensated. This yields a protocol for simultaneous, non-destructive, in situ stabilizer readout of multiple data qubits via global pulses alone. Using this protocol, we demonstrate non-destructive measurement of Pauli-Z stabilizers on four-qubit Cs plaquettes via a single global Rydberg pulse sequence. Our results demonstrate dual-species tweezer arrays as a promising route towards scalable QEC and open the door to new quantum control protocols leveraging both interspecies and intraspecies interactions.
We calculate interspecies Rydberg-Rydberg interaction strengths for the heavy alkali metals Rb and Cs. The presence of strong F\"orster resonances makes interspecies coupling a promising approach for long-range entanglement generation. We also provide an overview of the strongest F\"orster resonances for Rb-Rb and Cs-Cs using different principal quantum numbers for the two atoms. We show how interspecies coupling can be used for high fidelity quantum nondemolition state measurements with low cross-talk in qubit arrays.
Large-scale Rydberg atom arrays are used for highly coherent analogue quantum simulations and for digital quantum computations. However, advanced quantum protocols, such as quantum error correction, require midcircuit qubit operations, including the replenishment, reset and read-out of a subset of qubits. A compelling strategy for unlocking these capabilities is a dual-species architecture in which a second atomic species is controlled independently and entangled with the first through Rydberg interactions. Here, we realize a dual-species Rydberg array consisting of rubidium and caesium atoms and explore regimes of interactions and dynamics not accessible in single-species architectures. We achieve enhanced interspecies interactions by electrically tuning the Rydberg states close to a Förster resonance. In this regime, we demonstrate an interspecies Rydberg blockade and implement a quantum state transfer from one species to another. We then generate a Bell state between Rb and Cs hyperfine qubits through an interspecies controlled-phase gate. Finally, we combine interspecies entanglement with a native midcircuit read-out to achieve quantum non-demolition measurements. Rydberg atoms in optical tweezers are a promising platform for quantum information science. A platform composed of dual-species Rydberg arrays has been realized, offering access to unexplored interaction regimes and crosstalk-free midcircuit control.
Recently, neutral atom arrays have become known for their promising potential in quantum information processing. High-fidelity entangling operations are typically achieved by exciting atoms to high-lying Rydberg states through two-photon processes. To improve the performance of these systems at the hardware level, dual-species strategies have been applied to enhance readout, error correction, and reloading in neutral atom systems. However, the influence of laser crosstalk arising from two-photon excitation for dual-species systems has remained largely unexplored in the literature. Here, we develop a model that incorporates the influence of crosstalk in inter-species Rydberg gates with two-photon driving. We demonstrate that the influence of this crosstalk can be suppressed to arbitrarily small levels through appropriate gate design, with gate fidelities greater than 99.8%99.8\%99.8% achievable with conservative experimental parameters in the near-detuned case of an 85^{85}85Rb/87^{87}87Rb system. We also outline how this fidelity can be further enhanced through improvements to the Rydberg excitation.