Magnifying quantum phase fluctuations with Cooper-pair pairing

Smith, W. C.; Villiers, M.; Marquet, A.; Palomo, J.; Delbecq, M. R.; Kontos, T.; Campagne-Ibarcq, P.; Douçot, B.; Leghtas, Z.

doi:10.48550/arxiv.2010.15488

Cited by 5 publications

(6 citation statements)

References 16 publications

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“…However, we note that near-term small-scale experiments utilizing charge driving or capac-itive coupling in planar chips will still perform well at the expense of higher design and operational complexity. We believe that our results will on one hand stimulate further research and development efforts on fluxoniumbased quantum architectures, and on the other hand motivate similar scalability studies of novel superconducting platforms such as the cos(2 φ) [169][170][171][172][173][174][175], the bi-fluxon [176], and the 0 − π [177][178][179][180][181]…”

Section: Discussionmentioning

confidence: 59%

Scalable High-Performance Fluxonium Quantum Processor

Nguyen¹,

Koolstra²,

Kim³

et al. 2022

Preprint

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Section: Discussionmentioning

confidence: 59%

Scalable High-Performance Fluxonium Quantum Processor

Nguyen¹,

Koolstra²,

Kim³

et al. 2022

Preprint

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“…Of the eight qubits studied, some reside in the classical flux qubit limit [24] characterized by a strong localization of phase with zero point phase fluctuations of only 𝜑 zpf = (2𝐸 𝐶 /𝐸 𝐿 ) 1/4 = 0.56, while others reach the quasi-charge regime [10] characterized by a strongly reduced flux sensitivity due to a wavefunction probability delocalization |𝜑| > 𝜋 of up to 30% (𝜑 zpf = 2.4) at half flux (Φ ext = 0.5 Φ 0 ). This complements parallel work to delocalize the circuit ground state phase by means of Cooper pair co-tunneling [25] and represents an important step towards realizing passively protected circuits [26,27] such as the 0-𝜋 [28][29][30] or the cos (2𝜑) [31]. The qubit states of such devices would be spanned by two degenerate ground states protected by circuit symmetries and thus will rely on a very precise control of the qubit energies -properties that are ensured by top-down lithographically defined geometry in the present work.…”

Section: Introductionmentioning

confidence: 81%

Geometric superinductance qubits: Controlling phase delocalization across a single Josephson junction

Peruzzo,

Hassani,

Szep

et al. 2021

Preprint

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There are two elementary superconducting qubit types that derive directly from the quantum harmonic oscillator. In one the inductor is replaced by a nonlinear Josephson junction to realize the widely used charge qubits with a compact phase variable and a discrete charge wavefunction. In the other the junction is added in parallel, which gives rise to an extended phase variable, continuous wavefunctions and a rich energy level structure due to the loop topology. While the corresponding rf-SQUID Hamiltonian was introduced as a quadratic, quasi-1D potential approximation to describe the fluxonium qubit implemented with long Josephson junction arrays, in this work we implement it directly using a linear superinductor formed by a single uninterrupted aluminum wire. We present a large variety of qubits all stemming from the same circuit but with drastically different characteristic energy scales. This includes flux and fluxonium qubits but also the recently introduced quasi-charge qubit with strongly enhanced zero point phase fluctuations and a heavily suppressed flux dispersion. The use of a geometric inductor results in high precision of the inductive and capacitive energy as guaranteed by top-down lithography -a key ingredient for intrinsically protected superconducting qubits. The geometric fluxonium also exhibits a large magnetic dipole, which renders it an interesting new candidate for quantum sensing applications.

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“…The present work focusses on the properties of the plasmon encoding and we identified the characteristic E J /E L ratio as the relevant parameter to carefully control the band dispersion and the resulting flux noise sensitivity of the device. With a demonstrated flux dispersion of only 5.1 MHz over a full flux quantum it is significantly less noise sensitive compared to the high impedance approach investigated to date [12,13,60]. Combined with a lower flux noise amplitude inductor and lower TLS density capacitor materials, as well as an improved geometry to reduce surface loss participation, the IST concept opens a new path forward to introduce in-situ fine tuning of the transmon frequency without sacrificing protection against flux noise.…”

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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Magnifying quantum phase fluctuations with Cooper-pair pairing

Cited by 5 publications

References 16 publications

Scalable High-Performance Fluxonium Quantum Processor

Scalable High-Performance Fluxonium Quantum Processor

Geometric superinductance qubits: Controlling phase delocalization across a single Josephson junction

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

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