Geometric Superinductance Qubits: Controlling Phase Delocalization across a Single Josephson Junction

Peruzzo, Matilda; Hassani, Farid; Szép, Gregory; Trioni, Andrea; Redchenko, E. S.; Žemlička, Martin; Fink, J. M.

doi:10.1103/prxquantum.2.040341

Cited by 20 publications

(26 citation statements)

References 51 publications

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“…where √ A Φ ≈ 98 µΦ 0 is the flux noise amplitude and γ = ln fu 2πf l ≈ 9.9 represents the scaling parameter for the specific Ramsey sequence noise filter function with low and high frequency cutoffs f l = 250 mHz (inverse measurement time per data point) and f u = 1/T 2 = 31 kHz [38,57]. This flux noise amplitude is found to be larger than the typical values reported in the literature, which we attribute to the large effective loop perimeter created by the geometric superinductance [13,58]. It's contribution to the total dephasing is depicted in Fig.…”

Section: Experimental Realizationmentioning

confidence: 66%

“…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. an enhanced flux noise amplitude, could in principle be mitigated with a noise-insensitive design.…”

Section: Discussionmentioning

confidence: 88%

“…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%

“…In the low-capacitance (light) regime characterized by small E J /E C ∼ 1 the splitting is very large. In the case of ultra-high impedance the splitting opens up and forms flat Bloch-bands that form the basis states of the recently realized quasi-charge qubit [12,13]. In the highcapacitance (heavy) regime characterized by E J /E C 1 on the other hand the circuit is dominated by the plasmonic character.…”

Section: Theorymentioning

confidence: 99%

“…More recently this was also achieved in the case of rf-SQUID type qubits by realizing quasi-charge qubits that operate in the challenging to realize high impedance, i.e. low inductive to charging energy ratio E L /E C 1 [12,13], thus delocalizing the wave function in phase and flattening the flux dispersion.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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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Section: Experimental Realizationmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Hassani¹,

Peruzzo²,

Kapoor³

et al. 2022

Preprint

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Unimon qubit

et al. 2022

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Superconducting qubits seem promising for useful quantum computers, but the currently wide-spread qubit designs and techniques do not yet provide high enough performance. Here, we introduce a superconducting-qubit type, the unimon, which combines the desired properties of increased anharmonicity, full insensitivity to dc charge noise, reduced sensitivity to flux noise, and a simple structure consisting only of a single Josephson junction in a resonator. In agreement with our quantum models, we measure the qubit frequency, ω01/(2π), and increased anharmonicity α/(2π) at the optimal operation point, yielding, for example, 99.9% and 99.8% fidelity for 13 ns single-qubit gates on two qubits with (ω01, α) = (4.49 GHz, 434 MHz) × 2π and (3.55 GHz, 744 MHz) × 2π, respectively. The energy relaxation seems to be dominated by dielectric losses. Thus, improvements of the design, materials, and gate time may promote the unimon to break the 99.99% fidelity target for efficient quantum error correction and possible useful quantum advantage with noisy systems.

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Inductively shunted transmons exhibit noise insensitive plasmon states and a fluxon decay exceeding 3 hours

et al. 2023

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Currently available quantum processors are dominated by noise, which severely limits their applicability and motivates the search for new physical qubit encodings. In this work, we introduce the inductively shunted transmon, a weakly flux-tunable superconducting qubit that offers charge offset protection for all levels and a 20-fold reduction in flux dispersion compared to the state-of-the-art resulting in a constant coherence over a full flux quantum. The parabolic confinement provided by the inductive shunt as well as the linearity of the geometric superinductor facilitates a high-power readout that resolves quantum jumps with a fidelity and QND-ness of >90% and without the need for a Josephson parametric amplifier. Moreover, the device reveals quantum tunneling physics between the two prepared fluxon ground states with a measured average decay time of up to 3.5 h. In the future, fast time-domain control of the transition matrix elements could offer a new path forward to also achieve full qubit control in the decay-protected fluxon basis.

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Geometric Superinductance Qubits: Controlling Phase Delocalization across a Single Josephson Junction

Cited by 20 publications

References 51 publications

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

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

Unimon qubit

Inductively shunted transmons exhibit noise insensitive plasmon states and a fluxon decay exceeding 3 hours

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