Voltage-controlled superconducting quantum bus

Abstract

We demonstrate the ability of an epitaxial semiconductor-superconductor nanowire to serve as a field-effect switch to tune a superconducting cavity. Two superconducting gatemon qubits are coupled to the cavity, which acts as a quantum bus. Using a gate voltage to control the superconducting switch yields up to a factor of 8 change in qubit-qubit coupling between the on and off states without detrimental effect on qubit coherence. High-bandwidth operation of the coupling switch on nanosecond timescales degrades qubit coherence. arXiv:1802.01327v1 [cond-mat.mes-hall]

A quantum engineer's guide to superconducting qubits

“…The two-qubit gates available in the transmonlike superconducting qubit architecture can roughly be split into two broad families as outlined previously: one group requiring local magnetic fields to tune the transition frequency of qubits and one group consisting of all-microwave control. There exist several hybrid schemes that combine various aspects of these two categories and, in particular, the notions of tunable coupling and parametric driving are proving to be important ingredients in modern superconducting qubit processors 63,67,89,103,106,[207][208][209][210][211][212][213] . In this section, however, we start by introducing the iSWAP gate, and then review the CPHASE (controlled-phase) in Section IV F and the CR (cross-resonance) in Section IV G. We briefly review a few other two-qubit gates and discuss their merits in Sections IV G 4 and IV H.…”

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

“…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

“…This compatibility is a crucial step to reach a regime relevant for microwave (MW) readout of topological qubits based on Majorana bound states (MBSs) [5][6][7][8][9][10][11][12][13][14][15][16]. Various options include semiconductors [17][18][19][20][21][22][23] and van der Waals heterostructures [24][25][26].…”