Suppressed Charge Dispersion via Resonant Tunneling in a Single-Channel Transmon

Abstract

We demonstrate strong suppression of charge dispersion in a semiconductor-based transmon qubit across Josephson resonances associated with a quantum dot in the junction. On resonance, dispersion is drastically reduced compared to conventional transmons with corresponding Josephson and charging energies. We develop a model of qubit dispersion for a single-channel resonance, which is in quantitative agreement with experimental data.

Observation of Vanishing Charge Dispersion of a Nearly Open Superconducting Island

“…The natural magnetic field compatibility of superconductor-quantum dot-superconductor transmons also sets the stage for detecting and manipulating Majorana zero modes [19,58,59]. Finally, independent research reports similar results on the charge dispersion of a full-shell nanowire gatemon with a dc transport lead [60].…”

Destructive Little-Parks Effect in a Full-Shell Nanowire-Based Transmon

“…4(a). The interlaced sinusoidal qubit response as a function of V C (column average subtracted) represents the two charge parity branches, visible in the offset-chargesensitive regime, as investigated previously in conventional [31] and semiconducting junctions [12,13]. The simultaneous visibility of both parity branches indicates parity switching (poisoning) that is fast compared to the measurement time [31].…”

“…Variants of the conventional metallic transmon qubit [1,2] based on a semiconductor nanowires (NWs) with an epitaxial superconducting shell have appeared recently and shown great promise for qubit applications, offering atomically precise interfaces and electrostatic control of junction properties [3][4][5][6][7]. By now, qubit spectroscopy [3], coherence [4], two-qubit operation [5], gatecontrolled qubit coupling [8], and dc monitoring [9] have been demonstrated, along with investigations of applied magnetic field [7], junction Andreev bound states [6,10], anharmonicity [11], charge dispersion [12,13], spin [14], and parity protection [15]. However, axial flux effects from a fully surrounding Al shell on Josephson coupling have not been considered previously.…”

Majorana oscillations and parity crossings in semiconductor nanowire-based transmon qubits

“…Our projection method can be readily extended to other relevant regimes [37]. Other geometries currently under intensive experimental study, including split junctions [37], junctions with quantum dots [51,52], and superconducting FIG. 3.…”