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1. Erasure conversion in a high-fidelity Rydberg quantum simulator

   https://doi.org/10.1038/s41586-023-06516-4  

   Scholl, Pascal; Shaw, Adam L.; Tsai, Richard Bing-Shiun; Finkelstein, Ran; Choi, Joonhee; Endres, Manuel (October 2023, Nature)

   Abstract Minimizing and understanding errors is critical for quantum science, both in noisy intermediate scale quantum (NISQ) devices¹and for the quest towards fault-tolerant quantum computation^2,3. Rydberg arrays have emerged as a prominent platform in this context⁴with impressive system sizes^5,6and proposals suggesting how error-correction thresholds could be significantly improved by detecting leakage errors with single-atom resolution^7,8, a form of erasure error conversion^9–12. However, two-qubit entanglement fidelities in Rydberg atom arrays^13,14have lagged behind competitors^15,16and this type of erasure conversion is yet to be realized for matter-based qubits in general. Here we demonstrate both erasure conversion and high-fidelity Bell state generation using a Rydberg quantum simulator^5,6,17,18. When excising data with erasure errors observed via fast imaging of alkaline-earth atoms^19–22, we achieve a Bell state fidelity of$$\ge 0.997{1}_{-13}^{+10}$$ $\ge 0.9971_{-13}^{+10}$, which improves to$$\ge 0.998{5}_{-12}^{+7}$$ $\ge 0.9985_{-12}^{+7}$when correcting for remaining state-preparation errors. We further apply erasure conversion in a quantum simulation experiment for quasi-adiabatic preparation of long-range order across a quantum phase transition, and reveal the otherwise hidden impact of these errors on the simulation outcome. Our work demonstrates the capability for Rydberg-based entanglement to reach fidelities in the 0.999 regime, with higher fidelities a question of technical improvements, and shows how erasure conversion can be utilized in NISQ devices. These techniques could be translated directly to quantum-error-correction codes with the addition of long-lived qubits^7,22–24. 

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2. High-fidelity gates and mid-circuit erasure conversion in an atomic qubit

   https://doi.org/10.1038/s41586-023-06438-1  

   Ma, Shuo; Liu, Genyue; Peng, Pai; Zhang, Bichen; Jandura, Sven; Claes, Jahan; Burgers, Alex P.; Pupillo, Guido; Puri, Shruti; Thompson, Jeff D. (October 2023, Nature)

   The development of scalable, high-fidelity qubits is a key challenge in quantum information science. Neutral atom qubits have progressed rapidly in recent years, demonstrating programmable processors1,2 and quantum simulators with scaling to hundreds of atoms3,4. Exploring new atomic species, such as alkaline earth atoms5,6,7, or combining multiple species8 can provide new paths to improving coherence, control and scalability. For example, for eventual application in quantum error correction, it is advantageous to realize qubits with structured error models, such as biased Pauli errors9 or conversion of errors into detectable erasures10. Here we demonstrate a new neutral atom qubit using the nuclear spin of a long-lived metastable state in 171Yb. The long coherence time and fast excitation to the Rydberg state allow one- and two-qubit gates with fidelities of 0.9990(1) and 0.980(1), respectively. Importantly, a large fraction of all gate errors result in decays out of the qubit subspace to the ground state. By performing fast, mid-circuit detection of these errors, we convert them into erasure errors; during detection, the induced error probability on qubits remaining in the computational space is less than 10−5. This work establishes metastable 171Yb as a promising platform for realizing fault-tolerant quantum computing. 

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3. Demonstration of measurement-enhanced state preparation and erasure conversion in a molecular tweezer array

   https://doi.org/10.1103/8q8p-mx1l  

   Holland, Connor M; Lu, Yukai; Li, Samuel J; Welsh, Callum L; Cheuk, Lawrence W (June 2025, Physical Review X)

   Programmable optical tweezer arrays of molecules are an emerging platform for quantum simulation and quantum information science. For these applications, the reduction and mitigation of errors remain major challenges. In this work, we leverage the rich internal structure of molecules to mitigate two types of errors - internal state preparation and qubit leakage errors. First, we demonstrate robust measurement-enhanced tweezer preparation at a record fidelity using site-resolved error detection followed by tweezer movement. Second, using a new hyperfine qubit encoding well-suited for use as a quantum memory, we demonstrate site-resolved detection of qubit leakage errors (erasures) induced by blackbody radiation. This constitutes the first demonstration of erasure conversion in molecules, a capability that has found recent interest in quantum error correction. Our work opens the door to new possibilities with molecular tweezer arrays: Measurement-enhanced preparation opens access to mesoscopic defect-free molecular arrays that are important for quantum simulation of interacting many-body systems; erasure conversion in molecular arrays lays the technical ground- work for mid-circuit detection, an important capability for explorations in quantum information processing. 

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4. High-fidelity entanglement and detection of alkaline-earth Rydberg atoms

   Madjarov, Ivaylo; Covey, Jacob; Shaw, Adam; Choi, Joonhee; Kale, Anant; Cooper, Alexandre; Pichler, Hannes; Schkolnik, Vladimir; Williams, Jason; Endres, Manuel (January 2020, Nature physics)

   Trapped neutral atoms have become a prominent platform for quantum science, where entanglement fidelity records have been set using highly excited Rydberg states. However, controlled two-qubit entanglement generation has so far been limited to alkali species, leaving the exploitation of more complex electronic structures as an open frontier that could lead to improved fidelities and fundamentally different applications such as quantum-enhanced optical clocks. Here, we demonstrate a novel approach utilizing the two-valence electron structure of individual alkaline-earth Rydberg atoms. We find fidelities for Rydberg state detection, single-atom Rabi operations and two-atom entanglement that surpass previously published values. Our results pave the way for novel applications, including programmable quantum metrology and hybrid atom–ion systems, and set the stage for alkaline-earth based quantum computing architectures. 

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5. Rydberg mediated entanglement in a two-dimensional neutral atom qubit array

   Graham, TM; Kwon, M.; Grinkemeyer, B.; Marra, Z.; Jiang, X; Lichtman, M.T.; Sun, Y.; Ebert, M.; and M. Saffman, M. (August 2019, ArXiv.org)

   We demonstrate high fidelity two-qubit Rydberg blockade and entanglement in a two-dimensional qubit array. The qubit array is defined by a grid of blue detuned lines of light with 121 sites for trapping atomic qubits. Improved experimental methods have increased the observed Bell state fidelity to FBell = 0.86(2). Accounting for errors in state preparation and measurement (SPAM) we infer a fidelity of F−SPAM Bell = 0.89. Including errors in single qubit operations we infer that the Rydberg mediated CZ gate has a fidelity of F−SPAM CZ= 0.91. Comparison with a detailed error model shows that further improvement in fidelity will require colder atoms and lasers with reduced noise. 

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