Magnifying quantum phase fluctuations with Cooper-pair pairing

Abstract

Remarkably, complex assemblies of superconducting wires, electrodes, and Josephson junctions are compactly described by a handful of collective phase degrees of freedom that behave like quantum particles in a potential. The inductive wires contribute a parabolic confinement, while the tunnel junctions add a cosinusoidal corrugation. Usually, the ground state wavefunction is localized within a single potential well -- that is, quantum phase fluctuations are small -- although entering the regime of delocalization holds promise for metrology and qubit protection. A direct route is to loosen the inductive confinement and let the ground state phase spread over multiple Josephson periods, but this requires a circuit impedance vastly exceeding the resistance quantum and constitutes an ongoing experimental challenge. Here we take a complementary approach and fabricate a generalized Josephson element that can be tuned in situ between one- and two-Cooper-pair tunneling, doubling the frequency of the corrugation and thereby magnifying the number of wells probed by the ground state. We measure a tenfold suppression of flux sensitivity of the first transition energy, implying a twofold increase in the vacuum phase fluctuations.

arXiv comment11 pages, 8 figures

References in corpus (22)

• Encoding a qubit in an oscillator
• Superconducting Qubits: Current State of Play
• Fluxonium: single Cooper pair circuit free of charge offsets
• Persistent current in superconducting nanorings
• Implementation of low-loss superinductances for quantum circuits
• Granular aluminum: A superconducting material for high impedance quantum circuits
• Protected gates for superconducting qubits
• Superconducting Nanocircuits for Topologically Protected Qubits
• Pairing of Cooper Pairs in a Fully Frustrated Josephson Junction Chain
• Experimental realization of an intrinsically error-protected superconducting qubit
• Possible realization of an ideal quantum computer in Josephson junction array
• Universal fast flux control of a coherent, low-frequency qubit
• Nanowire Superinductance Fluxonium Qubit
• Superconducting circuit protected by two-Cooper-pair tunneling
• The superconducting quasicharge qubit
• Coherence properties of the 0-$\pi$ qubit
• Protected Josephson Rhombi Chains
• Surpassing the resistance quantum with a geometric superinductor
• Quantization of inductively-shunted superconducting circuits
• A gate-tunable, field-compatible fluxonium
• Degeneracy-preserving quantum non-demolition measurement of parity-type observables for cat-qubits
• Doubly Nonlinear Superconducting Qubit

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• A superconducting qubit with noise-insensitive plasmon levels and decay-protected fluxon states
• Gottesman-Kitaev-Preskill state preparation using periodic driving
• From nonreciprocal to charge-4e supercurrents in Ge-based Josephson devices with tunable harmonic content
• Hardware implementation of quantum stabilizers in superconducting circuits
• Stabilization of cat-state manifolds using nonlinear reservoir engineering
• The quartic Blochnium: an anharmonic quasicharge superconducting qubit
• Flux-Tunable Regimes and Supersymmetry in Twisted Cuprate Heterostructures
• A Linear Quantum Coupler for Clean Bosonic Control
• Protected phase gate for the $0$-$\pi$ qubit using its internal modes
• Gate- and flux-tunable sin(2$\phi$) Josephson element with proximitized Ge-based junctions