Entangling transmons with low-frequency protected superconducting qubits

Maiani, Andrea; Kjærgaard, Morten; Schrade, Constantin

doi:10.48550/arxiv.2203.04323

Cited by 2 publications

(2 citation statements)

References 44 publications

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“…Exceptions where different types of qubits are coupled are, for example, Refs. [43,65,66]. In this work, we consider the idea of using chips with heterogeneous qubits.…”

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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“…Exceptions where different types of qubits are coupled are, for example, Refs. [43,65,66]. In this work, we consider the idea of using chips with heterogeneous qubits.…”

Section: Introductionmentioning

confidence: 99%

Microwave-activated gates between a fluxonium and a transmon qubit

Ciani¹,

Varbanov²,

Jolly³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…This exact doubling of Shapiro steps is due to pure double-Cooper pair tunneling, leading to the formation of an effective cos(2ϕ) Josephson potential. In future experiments, the transition to a doubled Shapiro step pattern could be useful for calibrating parity-protected qubits [43][44][45][46], which require a cos(2ϕ) Josephson potential to robustly store quantum information.…”

mentioning

confidence: 99%

The Josephson diode effect in supercurrent interferometers

Souto,

Leijnse,

Schrade

2022

Preprint

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A Josephson diode is a non-reciprocal circuit element that supports a larger dissipationless supercurrent in one direction than in the other. In this work, we propose and theoretically study a class of Josephson diodes based on supercurrent interferometers containing mesoscopic Josephson junctions, such as point contacts or quantum dots, which are not diodes themselves but possess non-sinusoidal current-phase relations. We show that such Josephson diodes have several important advantages, like being electrically tunable and requiring neither Zeeman splitting nor spin-orbit coupling, only time-reversal breaking by a magnetic flux. We also show that our diodes have a characteristic AC response, revealed by the Shapiro steps. Even the simplest realization of our Josephson diode paradigm that relies on only two junctions can achieve efficiencies of up to ∼ 40% and, interestingly, far greater efficiencies are achievable by concatenating multiple interferometer loops.

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Entangling transmons with low-frequency protected superconducting qubits

Cited by 2 publications

References 44 publications

Microwave-activated gates between a fluxonium and a transmon qubit

Microwave-activated gates between a fluxonium and a transmon qubit

The Josephson diode effect in supercurrent interferometers

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