Dispersive sensing in hybrid InAs/Al nanowires

Abstract

Dispersive charge sensing is realized in hybrid semiconductor-superconductor nanowires in gate-defined single-and double-island device geometries. Signal-to-noise ratios (SNRs) were measured both in the frequency and time domain. Frequency-domain measurements were carried out as a function of frequency and power and yield a charge sensitivity of 1 · 10 −3 e/ √ Hz for an ∼11 MHz measurement bandwidth. Time-domain measurements yield SNR > 1 for 20 µs integration time. At zero magnetic field, photon-assisted tunneling was detected dispersively in a double-island geometry, indicating coherent hybridization of the two superconducting islands. At an axial magnetic field of 0.6 T, subgap states are detected dispersively, demonstrating the suitability of the method for sensing in the topological regime.Readout of quantum systems on timescales short compared to coherence or relaxation times is typically performed by one of a few schemes: (i) the device is incorporated into a resonant circuit, allowing state-dependent changes in the damping or shift of the resonance to be measured, 1,2 (ii) the quantum state is converted to charge, which is then detected by a nearby electrometer, [3][4][5][6] or (iii) a state-dependent capacitive coupling to the system results in a frequency shift in the coupled resonant circuit that depends on the quantum state, 7,8 the latter referred to as dispersive readout. In the context of topological qubits, several proposals for non-locally encoding fermion parity in Majorana zero modes have been made 9-13 . Some proposals use parity-to-charge conversion for readout 10 , while others use state-dependent hybridization of the Majorana mode with an ancillary system, leading to a dispersive readout signal. 11,12 Integrating readout circuitry into an existing electrostatic gate or ohmic contact is useful for reducing device footprint and lead count. 2,8,[14][15][16][17][18][19][20][22][23][24][25] In this case, dispersive readout is performed by monitoring state-dependent shifts in the resonance frequency f R = (LC tot ) −1/2 of an LC circuit connected to a gate, where f R is detuned from the qubit transition frequency. The total capacitance, C tot , comprises geometric capacitance, C g (including parasitic contributions), quantum capacitance, C Q , and tunnel capacitance, C T . 7,26 When the quantum system consists of a Coulomb island tunnel coupled to a reservoir, C Q arises from continuous charge transitions, and is proportional to the curvature of energy with respect to the confining gate voltage. 27 The maximum magnitude of C Q occurs at gate voltages corresponding to charge degeneracy, with opposite signs for ground and first excited states. C T is significant when the energy relaxation rate exceeds f R . The dependence of f R on C Q provides the quantum state selectivity of the dispersive shift. Monitoring phase or magnitude of the signal reflected from the resonant circuit thus allows readout of the quantum state of the system.Recent work on gate-based dispersive sensing has addressed semicondu...

Large dispersive interaction between a CMOS double quantum dot and microwave photons

“…We note that to achieve the fast readout presented in this manuscript, we did not use a JPA showing that there is room for further improvement. Finally, we also note that our approach should impact research aiming at improving the readout fidelity of Majorana-based quantum devices [28,29]. We present a photograph of the hybrid integrated system described in the main article, showing the silicon NWFET and superconducting inductor on separate substrates, see Fig.…”

“…Although g 0 κ, the fast decay rate of the charge degree of freedom of the DQD precludes reaching the strong coupling limit, a goal within reach for the spin degree of freedom. We note that the microwave circuitry presented here should readily improve the readout fidelity not only of CMOS-based devices but of any semiconductor-based system, especially those with a large gate lever arm such as topological qubits [28,29].…”

Electronic transport in double-nanowire superconducting islands with multiple terminals

“…Subjects explored are quasiparticle relaxation, poisoning lifetimes [32][33][34] and the evolution of SI Coulomb peaks in a magnetic field [35][36][37][38][39][40][41][42][43][44] to shed light on potential topological properties [45]. Furthermore, devices exploring the Little-Parks effect [46], interferometry [47] and reflectometry techniques [48][49][50] yielded additional insight. The most commonly studied material system has been InAs/Al but alternative superconductors such as NbTiN, Sn and Pb [51][52][53][54] or different nanowire materials [38,55] have been explored.…”

Rapid microwave-only characterization and readout of quantum dots using multiplexed gigahertz-frequency resonators

“…We now move on to the capacitively coupled gate resonators and investigate DGS in the double quantum dot (DQD) regime [17,25,[43][44][45][46][47][48][49][50][51][52]. To tune the system into a DQD, the voltages of gates T4, T5, and T6 are each decreased into the tunneling regime.…”