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arXiv:2401.02308 · Physical Review Research

Interspecies Förster resonances for Rb-Cs Rydberg d -states for enhanced multi-qubit gate fidelities

P. M. Ireland, D. M. Walker, Jonathan D. Pritchard

Published Mar 18, 2024• 12 citations
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Abstract

We present an analysis of interspecies interactions between Rydberg d -states of rubidium and cesium. We identify the Förster resonance channels offering the strongest interspecies couplings, demonstrating the viability for performing high-fidelity two- and multi-qubit C k Z gates up to k = 4 , including accounting for blockade errors evaluated via numerical diagonalization of the pair potentials. Our results show d -state orbitals offer enhanced suppression of intraspecies couplings compared to s -states, making them well suited for use in large-scale neutral atom quantum processors. Published by the American Physical Society 2024

DOI
10.1103/physrevresearch.6.013293

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We present an analysis of interspecies interactions between Rydberg d -states of rubidium and cesium. We identify the Förster resonance channels offering the strongest interspecies couplings, demonstrating the viability for performing high-fidelity two- and multi-qubit C k Z gates up to k = 4 , including accounting for blockade errors evaluated via numerical diagonalization of the pair potentials. Our results show d -state orbitals offer enhanced suppression of intraspecies couplings compared to s -states, making them well suited for use in large-scale neutral atom quantum processors. Published by the American Physical Society 2024
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.
Neutral-atom entangling gates are commonly analyzed with a single effective Rydberg-pair state, but near Förster resonances the pair manifold contains resonantly coupled interaction channels that change both the control landscape and the achievable fidelity. We develop a two-eigenstate model for this regime and show that when allowing for coupling to both pair states in the resonance, the gate fidelity is bounded by F≤1−(π/2)/(VτR)\mathcal{F}\leq 1-(π/2)/(Vτ_R)F≤1−(π/2)/(VτR​), for interaction strength VVV and Rydberg lifetime τRτ_RτR​. We construct a gate protocol that saturates this bound in the large-Rabi-frequency limit, improving the existing fidelity limit by approximately 40%40\%40%. We also evaluate common gate protocols near Förster resonances and find that retaining the exchange dynamics increases predicted fidelities by up to two orders of magnitude over earlier treatments.
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.
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.
Quantum information processing with neutral atoms relies on Rydberg excitation for entanglement generation. While the use of heavy divalent or open-shell elements, such as strontium or ytterbium, has benefits due to their optically active core and a variety of possible qubit encodings, their Rydberg structure is generally complex. For some isotopes in particular, hyperfine interactions are relevant even for highly excited electronic states. We employ multichannel quantum defect theory to infer the Rydberg structure of isotopes with nonzero nuclear spin and perform nonperturbative Rydberg-pair interaction calculations. We find that due to the high level density and sensitivities to external fields, experimental parameters must be precisely controlled. Specifically in Sr 87 , we study an intrinsic Förster resonance, unique to divalent atoms with hyperfine-split thresholds, which simultaneously provides line stability with respect to external field fluctuations and enhanced long-range interactions. Additionally, we provide parameters for pair states that can be effectively described by single-channel Rydberg series. The explored pair states provide exciting opportunities for applications in the blockade regime, as well as for more exotic long-range interactions such as largely flat, distance-independent potentials. Published by the American Physical Society 2024