Engineering superconducting qubits to reduce quasiparticles and charge noise

Pan, X.; Zhou, Yuxuan; Yuan, Haolan; Nie, Lifu; Wei, Weiwei; Zhang, Libo; Li, Jian; Liu, Song; Jiang, Zhi Hao; Catelani, Gianluigi; Hu, Ling; Yan, Fei; Yu, Dapeng

doi:10.1038/s41467-022-34727-2

Cited by 35 publications

(7 citation statements)

References 44 publications

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“…Such a redesign will concentrate the power emitted by the SFQ driver below the aluminum gap edge, so that QP generation is not possible. The qubit and the SFQqubit coupler could also be modified to suppress their antenna coupling to free space at frequencies just above the aluminum gap [50,51,54]. To protect the qubit from any residual nonequilibrium QPs, appropriate superconductor gap engineering [31,[57][58][59][60] could be harnessed to promote the rapid outflow of QPs from the qubit junction and to prevent the inflow to the junction of QPs from remote parts of the qubit circuit.…”

Section: Discussionmentioning

confidence: 99%

“…It has recently been shown that absorption of pairbreaking photons is a dominant source of QP poisoning in Josephson devices [51,[53][54][55]. For typical geometries, the superconducting qubit structure forms a resonant antenna that provides an efficient power match from free space to the high-impedance Josephson junction at mmwave frequencies [50].…”

Section: Antenna Coupling Of the Sfq Transient To The Qubitmentioning

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: Discussionmentioning

confidence: 99%

Section: Antenna Coupling Of the Sfq Transient To The Qubitmentioning

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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show abstract

“…There are many mechanisms affecting qubit lifetime, [2,3] including losses induced by two-level system (TLS), [2,4,5] Purcell effect, [6,7] and quasiparticles (QP). [8,9] The energy relaxation rate Γ 1 is given by…”

Section: Introductionmentioning

confidence: 99%

Optimize Purcell filter design for reducing influence of fabrication variation

Cai 蔡,

Zhou 周,

Yu 于

et al. 2024

Chinese Phys. B

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To protect superconducting qubits and enable rapid readout, optimally designed Purcell filters are essential. To suppress the off-resonant driving of untargeted readout resonators, individual Purcell filters were used for each readout resonator. However, achieving consistent frequency between a readout resonator and a Purcell filter is a significant challenge. A systematic computational analysis was conducted to investigate how fabrication variation impacts filter performance, focusing on the coupling capacitor structure and coplanar waveguide (CPW) transmission line specifications. The results indicate that the T-type enclosing capacitor (EC), which exhibits lower structural sensitivity, is more advantageous for achieving target capacitance compared to the C-type EC and the interdigital capacitor (IDC). By utilizing a large-sized CPW with the T-type EC structure, fluctuations in the effective coupling strength can be reduced to 10% given typical micro-nanofabrication variances. The numerical simulations presented in this work minimize the influence of fabrication deviations, thereby significantly improving the reliability of Purcell filter designs.

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“…Several mitigation strategies have been proposed to combat these ionizing impact events at the level of the quantum device, such as the direct trapping of quasiparticles through gap engineering [17][18][19][20] as well as impeding the propagation of phonons by substrate modification [21][22][23][24]. A complementary approach is the use of so-called phonon traps [15,23,[25][26][27].…”

Section: Introductionmentioning

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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Engineering superconducting qubits to reduce quasiparticles and charge noise

Cited by 35 publications

References 44 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

Optimize Purcell filter design for reducing influence of fabrication variation

Mitigation of Quasiparticle Loss in Superconducting Qubits by Phonon Scattering

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