6 research outputs found
Revealing charge-tunneling processes between a quantum dot and a superconducting island through gate sensing
We report direct detection of charge-tunneling between a quantum dot and a
superconducting island through radio-frequency gate sensing. We are able to
resolve spin-dependent quasiparticle tunneling as well as two-particle
tunneling involving Cooper pairs. The quantum dot can act as an RF-only sensor
to characterize the superconductor addition spectrum, enabling us to access
subgap states without transport. Our results provide guidance for future
dispersive parity measurements of Majorana modes, which can be realized by
detecting the parity-dependent tunneling between dots and islands.Comment: 6 pages, 4 figures, supplemental material included as ancillary fil
Controllable Single Cooper Pair Splitting in Hybrid Quantum Dot Systems
Cooper pair splitters hold utility as a platform for investigating the
entanglement of electrons in Cooper pairs, but probing splitters with
voltage-biased Ohmic contacts prevents the retention of electrons from split
pairs since they can escape to the drain reservoirs. We report the ability to
controllably split and retain single Cooper pairs in a multi-quantum-dot device
isolated from lead reservoirs, and separately demonstrate a technique for
detecting the electrons emerging from a split pair. First, we identify a
coherent Cooper pair splitting charge transition using dispersive gate sensing
at GHz frequencies. Second, we utilize a double quantum dot as an electron
parity sensor to detect parity changes resulting from electrons emerging from a
superconducting island.Comment: 18 pages, 12 figures. D.J. and C.G.P. contributed equally to this
wor
Rapid Detection of Coherent Tunneling in an InAs Nanowire Quantum Dot through Dispersive Gate Sensing
Dispersive sensing is a powerful technique that enables scalable and
high-fidelity readout of solid-state quantum bits. In particular, gate-based
dispersive sensing has been proposed as the readout mechanism for future
topological qubits, which can be measured by single electrons tunneling through
zero-energy modes. The development of such a readout requires resolving the
coherent charge tunneling amplitude from a quantum dot in a Majorana-zero-mode
host system faithfully on short time scales. Here, we demonstrate rapid
single-shot detection of a coherent single-electron tunneling amplitude between
InAs nanowire quantum dots. We have realized a sensitive dispersive detection
circuit by connecting a sub-GHz, lumped element microwave resonator to a
high-lever arm gate on one of dots. The resulting large dot-resonator coupling
leads to an observed dispersive shift that is of the order of the resonator
linewidth at charge degeneracy. This shift enables us to differentiate between
Coulomb blockade and resonance, corresponding to the scenarios expected for
qubit state readout, with a signal to noise ratio exceeding 2 for an
integration time of 1 microsecond. Our result paves the way for single shot
measurements of fermion parity on microsecond timescales in topological qubits.Comment: 6 pages, 4 figure
Radio-frequency C-V measurements with sub-attofarad sensitivity
We demonstrate the use of radio-frequency (rf) resonators to measure the
capacitance of nano-scale semiconducting devices in field-effect transistor
configurations. The rf resonator is attached to the gate or the lead of the
device. Consequently, tuning the carrier density in the conducting channel of
the device affects the resonance frequency, quantitatively reflecting its
capacitance. We test the measurement method on InSb and InAs nanowires at
dilution-refrigerator temperatures. The measured capacitances are consistent
with those inferred from the periodicity of the Coulomb blockade of quantum
dots realized in the same devices. In an implementation of the resonator using
an off-chip superconducting spiral inductor we find sensitivity values reaching
down to 75~zF/\sqHz at 1~kHz measurement bandwidth, and noise down to 0.45~aF
at 1~Hz bandwidth. We estimate the sensitivity of the method for a number of
other implementations. In particular we predict typical sensitivity of about
40~zF/\sqHz at room temperature with a resonator comprised of off-the-shelf
components. Of several proposed applications, we demonstrate two: the
capacitance measurement of several identical 80~nm-wide gates with a single
resonator, and the field-effect mobility measurement of an individual nanowire
with the gate capacitance measured in-situ
Rapid Microwave-Only Characterization and Readout of Quantum Dots Using Multiplexed Gigahertz-Frequency Resonators
Superconducting resonators enable fast characterization and readout of
mesoscopic quantum devices. Finding ways to perform measurements of interest on
such devices using resonators only is therefore of great practical relevance.
We report the experimental investigation of an InAs nanowire multi-quantum dot
device by probing GHz resonators connected to the device. First, we demonstrate
accurate extraction of the DC conductance from measurements of the
high-frequency admittance. Because our technique does not rely on DC
calibration, it could potentially obviate the need for DC measurements in
semiconductor qubit devices. Second, we demonstrate multiplexed gate sensing
and the detection of charge tunneling on microsecond time scales. The GHz
detection of dispersive resonator shifts allows rapid acquisition of
charge-stability diagrams, as well as resolving charge tunneling in the device
with a signal-to-noise ratio of up to 15 in one microsecond. Our measurements
show that GHz-frequency resonators may serve as a universal tool for fast
tune-up and high-fidelity readout of semiconductor qubits