Scalable High-Performance Fluxonium Quantum Processor

Nguyen, Long B.; Koolstra, Gerwin; Kim, Yosep; Morvan, Alexis; Chistolini, Trevor; Singh, Surinder; Nesterov, Konstantin; Jünger, Christian; Chen, Larry; Pedramrazi, Zahra; Mitchell, Bradley; Kreikebaum, John Mark; Puri, Shruti; Santiago, David I.; Siddiqi, Irfan

doi:10.48550/arxiv.2201.09374

Cited by 6 publications

(12 citation statements)

References 178 publications

(315 reference statements)

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“…In comparison, frequency requirements for fluxoniums are much less stringent, which guarantees a better fabrication yield of fluxonium-based processors. The road map for a scalable fluxonium-based processor, including frequency allocation and estimates for the fabrication yield, has been recently presented in preprint [44]. There, it was argued that the two-qubit gate realized via the CR effect is a viable solution for a scalable design for such a processor.…”

Section: Discussionmentioning

confidence: 99%

Controlled-NOT gates for fluxonium qubits via selective darkening of transitions

Nesterov¹,

Wang²,

Manucharyan³

et al. 2022

Preprint

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We analyze the cross-resonance effect for fluxonium circuits and investigate a two-qubit gate scheme based on selective darkening of a transition. In this approach, two microwave pulses at the frequency of the target qubit are applied simultaneously with a proper ratio between their amplitudes to achieve a controlled-not operation. We study in detail coherent gate dynamics and calculate gate error. With nonunitary effects accounted for, we demonstrate that gate error below 10 −4 is possible for realistic hardware parameters. This number is facilitated by long coherence times of computational transitions and strong anharmonicity of fluxoniums, which easily prevents excitation to higher excited states during the gate microwave drive.

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Section: Discussionmentioning

confidence: 99%

Controlled-NOT gates for fluxonium qubits via selective darkening of transitions

Nesterov¹,

Wang²,

Manucharyan³

et al. 2022

Preprint

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“…The fluxonium qubit platform has recently been identified as an alternative way forward to scaling up superconducting qubit processors [61,62] due to promising coherence times, higher design flexibility and anharmonicity. The use of geometric inductors could offer advantages for the reproducibility of E L [13] and the current work shows that one of its major drawbacks, i.e.…”

Section: Discussionmentioning

confidence: 99%

A superconducting qubit with noise-insensitive plasmon levels and decay-protected fluxon states

Hassani¹,

Peruzzo²,

Kapoor³

et al. 2022

Preprint

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The inductively shunted transmon (IST) is a superconducting qubit with exponentially suppressed fluxon transitions and a plasmon spectrum approximating that of the transmon. It shares many characteristics with the transmon but offers charge offset insensitivity for all levels and precise flux tunability with quadratic flux noise suppression. In this work we propose and realize IST qubits deep in the transmon limit where the large geometric inductance acts as a mere perturbation. With a flux dispersion of only 5.1 MHz we reach the 'sweet-spot everywhere' regime of a SQUID device with a stable coherence time over a full flux quantum. Close to the flux degeneracy point the device reveals tunneling physics between the two quasi-degenerate ground states with typical observed lifetimes on the order of minutes. In the future, this qubit regime could be used to avoid leakage to unconfined transmon states in high-power read-out or driven-dissipative bosonic qubit realizations. Moreover, the combination of well controllable plasmon transitions together with stable fluxon states in a single device might offer a way forward towards improved qubit encoding schemes.

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“…The enhanced protection of the fluxonium comes at the price of requiring a more involved scheme for the manipulation of its quantum state. The low fundamental frequency of the fluxonium (below 1GHz) complicates the execution of single-qubit gates due to the lesser accuracy of the rotating wave approximation compared to the transmon case [53]. In addition, the reduced matrix elements of charge and flux operators, that control the strength of the coupling between computational levels, needs to be compensated using higher drive power.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, the measurement of a fluxonium qubit can have advantages as compared to a transmon qubit. The off-resonant fluxonium-resonator coupling can give rise to relatively-large dispersive shifts [53,55] which enable fast measurement. For granular aluminium based fluxonium qubits, highly-accurate quantum measurements using strong drive power -populating the read-out cavity with a large number of photonshave been reported [56,57].…”

Section: Introductionmentioning

confidence: 99%

Microwave-activated gates between a fluxonium and a transmon qubit

Ciani¹,

Varbanov²,

Jolly³

et al. 2022

Preprint

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We propose and analyze two types of microwave-activated gates between a fluxonium and a transmon qubit, namely a cross-resonance (CR) and a CPHASE gate. The large frequency difference between a transmon and a fluxonium makes the realization of a two-qubit gate challenging. For a medium-frequency fluxonium qubit, the transmon-fluxonium system allows for a cross-resonance effect mediated by the higher levels of the fluxonium over a wide range of transmon frequencies. This allows one to realize the cross-resonance gate by driving the fluxonium at the transmon frequency, mitigating typical problems of the cross-resonance gate in transmon-transmon chips related to frequency targeting and residual ZZ coupling. However, when the fundamental frequency of the fluxonium enters the low-frequency regime below 100 MHz, the cross-resonance effect decreases leading to long gate times. For this range of parameters, a fast microwave CPHASE gate can be implemented using the higher levels of the fluxonium. In both cases, we perform numerical simulations of the gate showing that a gate fidelity above 99% can be obtained with gate times between 100 and 300 ns. Next to a detailed gate analysis, we perform a study of chip yield for a surface code lattice of fluxonia and transmons interacting via the proposed cross-resonance gate. We find a much better yield as compared to a transmon-only architecture with the cross-resonance gate as native two-qubit gate.

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Scalable High-Performance Fluxonium Quantum Processor

Cited by 6 publications

References 178 publications

Controlled-NOT gates for fluxonium qubits via selective darkening of transitions

Controlled-NOT gates for fluxonium qubits via selective darkening of transitions

A superconducting qubit with noise-insensitive plasmon levels and decay-protected fluxon states

Microwave-activated gates between a fluxonium and a transmon qubit

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