Phonon downconversion to suppress correlated errors in superconducting qubits

Vito, Iaia,; Ku, Jaseung; Ballard, Andrew; Larson, C. P.; Yelton, E.; Liu, Chuan-Hong; Patel, S.; McDermott, Robert; Plourde, B. L. T.

doi:10.1038/s41467-022-33997-0

Cited by 28 publications

(6 citation statements)

References 27 publications

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“…We find a monotonic decrease in excess P 1 toward the baseline value following application of the poisoning pulse. In a similar experiment involving injection of pair-breaking phonons into the qubit substrate, Iaia et al observed a QP-induced enhancement of qubit relaxation rate that peaks at a time ∼ 30 µs following application of the poisoning pulse, consistent with diffusive propagation of phonons from the injector junction to the qubit over the ∼4-mm separation between the elements [52]. We take the much faster response of the qubit to the poisoning pulse observed in our experiments as further evidence that coupling of the SFQ driver to the qubit is mediated by photons as opposed to phonons.…”

Section: Dynamics Of Qp Poisoningmentioning

confidence: 94%

“…It is known that qubit structures are efficient absorbers of pair-breaking radiation in the mm-wave range [50,51]; for picosecond SFQ pulses with bandwidth of order 100s of gigahertz, the electromagnetic transient could lead to emission of pair-breaking photons that are then absorbed at the qubit junction. We expect to be able to distinguish these two processes by examining the temporal dynamics of QP poisoning in our experiment: while the photonassisted QP poisoning mechanism will lead to immediate suppression of qubit coherence, the phonon mechanism will involve a time delay of order 10s of µs between application of the SFQ pulse and the onset of enhanced QP relaxation associated with the propagation of phonons from the SFQ driver to the qubit [52].…”

Section: Dynamics Of Qp Poisoningmentioning

confidence: 99%

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Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multi-Chip Module

Liu¹,

Ballard²,

Olaya³

et al. 2023

Preprint

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The single flux quantum (SFQ) digital superconducting logic family has been proposed for the scalable control of next-generation superconducting qubit arrays. In the initial implementation, SFQ-based gate fidelity was limited by quasiparticle (QP) poisoning induced by the dissipative onchip SFQ driver circuit. In this work, we introduce a multi-chip module architecture to suppress phonon-mediated QP poisoning. Here, the SFQ elements and qubits are fabricated on separate chips that are joined with In bump bonds. We use interleaved randomized benchmarking to characterize the fidelity of SFQ-based gates, and we demonstrate an error per Clifford gate of 1.2(1)%, an orderof-magnitude reduction over the gate error achieved in the initial realization of SFQ-based qubit control. We use purity benchmarking to quantify the contribution of incoherent error at 0.96(2)%; we attribute this error to photon-mediated QP poisoning mediated by the resonant mm-wave antenna modes of the qubit and SFQ-qubit coupler. We anticipate that a straightforward redesign of the SFQ driver circuit to limit the bandwidth of the SFQ pulses will eliminate this source of infidelity, allowing SFQ-based gates with fidelity approaching theoretical limits, namely 99.9% for resonant sequences and 99.99% for more complex pulse sequences involving variable pulse-to-pulse separation.

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Section: Dynamics Of Qp Poisoningmentioning

confidence: 94%

Section: Dynamics Of Qp Poisoningmentioning

confidence: 99%

Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multi-Chip Module

Liu¹,

Ballard²,

Olaya³

et al. 2023

Preprint

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“…Note added.-Recently, we have become aware of a similar experiment by Iaia et al [58]. In their work, the authors compare the impact of high-energy phonons on two separate transmon chips, where one chip has a 10µm-thick Cu film deposited on its backside.…”

Section: Acknowledgmentsmentioning

confidence: 99%

Mitigation of Quasiparticle Loss in Superconducting Qubits by Phonon Scattering

et al. 2023

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Quantum error correction will be an essential ingredient in realizing fault-tolerant quantum computing. However, most correction schemes rely on the assumption that errors are sufficiently uncorrelated in space and time. In superconducting qubits, this assumption is drastically violated in the presence of ionizing radiation, which creates bursts of high-energy phonons in the substrate. These phonons can break Cooper pairs in the superconductor and, thus, create quasiparticles over large areas, consequently reducing qubit coherence across the quantum device in a correlated fashion. A potential mitigation technique is to place large volumes of normal or superconducting metal on the device, capable of reducing the phonon energy to below the superconducting gap of the qubits. To investigate the effectiveness of this method, we fabricate a quantum device with four nominally identical nanowire-based transmon qubits. On the device, half of the niobium-titanium-nitride ground plane is replaced with aluminum (Al), which has a significantly lower superconducting gap. We deterministically inject high-energy phonons into the substrate by voltage biasing a galvanically isolated Josephson junction. In the presence of the small-gap material, we find a factor of 2-5 less degradation in the injection-dependent qubit lifetimes and observe that the undesired excited qubit state population is mitigated by a similar factor. We furthermore turn the Al normal with a magnetic field, finding no change in the phonon protection. This suggests that the efficacy of the protection in our device is not limited by the size of the superconducting gap in the Al ground plane. Our results provide a promising foundation for protecting superconducting-qubit processors against correlated errors from ionizing radiation.

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“…3.2), as direct means to attenuate the cosmic muon flux. Other initiatives in the field have been addressing the same problem with direct on-chip mitigation strategies, such as lower-gap superconducting quasiparticle traps [11], phonon traps [10], or suspending the device on a membrane [51]. All strategies have evidenced a decrease on the impact of ionizing events on the qubits and/or resonators employed as sensors.…”

Section: Qubit Decoherence Due To Ionizing Radiationmentioning

confidence: 99%

“…Therefore, techniques to mitigate the impact of ionizing radiation events are already necessary today. While on-chip mitigation strategies, such as phonon [10] or quasiparticle traps [11][12][13], are being developed, it is also necessary to understand the physics behind ionizing radiation, particularly the cosmic muon events, in order to find ways to attenuate their flux. In this work, we propose two such methods.…”

Section: Introductionmentioning

confidence: 99%

Cosmic muon flux attenuation methods for superconducting qubit experiments

Bertoldo¹,

Martínez²,

Nedyalkov³

et al. 2023

Preprint

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We propose and demonstrate two mitigation methods to attenuate the cosmic muon flux compatible with experiments involving superconducting qubits. Using a specifically-built cosmic muon detector, we find that chips oriented towards the horizon compared to chips looking at the sky overhead experience a decrease of a factor 1.6 of muon counts at the surface. Then, we identify shielded shallow underground sites, ubiquitous in urban environments, where significant additional attenuation, up to a factor 35 for 100-meter depths, can be attained. The two methods here described are the first proposed to directly reduce the effects from cosmic rays on qubits by attenuating the noise source, complementing existing on-chip mitigation strategies. We expect that both on-chip and off-chip methods combined will become ubiquitous in quantum technologies based on superconducting qubit circuits.

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Phonon downconversion to suppress correlated errors in superconducting qubits

Cited by 28 publications

References 27 publications

Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multi-Chip Module

Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multi-Chip Module

Mitigation of Quasiparticle Loss in Superconducting Qubits by Phonon Scattering

Cosmic muon flux attenuation methods for superconducting qubit experiments

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