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Comprehensive explanation of ZZ coupling in superconducting qubits

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arxiv 2408.15402 v2 pith:DYNYDCKE submitted 2024-08-27 quant-ph

classification quant-ph
keywords couplingqubitsquantumregionschallengecomputerscouplingsfidelities
verification ladder T0 review T1 audit T2 compute T3 formal
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A major challenge for scaling up superconducting quantum computers is unwanted couplings between qubits, which lead to always-on ZZ couplings that impact gate fidelities by shifting energy levels conditional on qubit states. To tackle this challenge, we introduce analytical and numerical techniques, including a diagrammatic perturbation theory and a state-assignment algorithm. Together, these tools enable us to explain the emergence of ZZ coupling in three linked pictures, where each picture tells us more about the underlying mechanisms creating the ZZ coupling. These pictures generalize previous efforts, which focused on specific setups and a single mechanism. The deeper understanding that we provide of the mechanisms behind the ZZ coupling facilitate finding parameter regions of weak and strong ZZ coupling. We showcase our techniques for a system consisting of two fixed-frequency transmon qubits connected by a flux-tunable transmon coupler. There, we find three types of parameter regions with zero or near-zero ZZ coupling, all of which are accessible with current technology. We furthermore find regions of strong ZZ coupling nearby, which may be used to implement adiabatic controlled-phase gates and quantum simulations. Our framework is applicable to many types of qubits and opens up for the design of large-scale quantum computers with improved gate fidelities.

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Cited by 5 Pith papers

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    quant-ph 2025-07 conditional novelty 6.0 of 10

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  3. Anomalous transparency of photons in non-Markovian coupled waveguides

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  4. Low Crosstalk in a Scalable Superconducting Quantum Lattice

    quant-ph 2025-05 conditional novelty 5.0 of 10

    A 16-qubit square lattice in a tileable 3D-integrated package shows localized inter-qubit couplings and low simultaneous single-qubit gate errors.

  5. Direct Implementation of High-Fidelity Three-Qubit Gates for Superconducting Processor with Tunable Couplers

    quant-ph 2025-01 conditional novelty 4.0 of 10

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