23 research outputs found
Refrigerator based on the Coulomb barrier for single-electron tunneling
We propose a remarkably simple electronic refrigerator based on the Coulomb barrier for single-electron tunneling. A fully normal single-electron transistor is voltage V biased at a gate position such that tunneling through one of the junctions costs an energy of about kBT≪eV,EC, where T is the temperature and EC is the transistor charging energy. The tunneling in the junction with positive energy cost cools both leads attached to it. Immediate practical realizations of such a refrigerator make use of Andreev mirrors which suppress heat current while maintaining full electric contact.Peer reviewe
Fluctuation relations for driven coupled classical two-level systems with incomplete measurements
Microwave photon-mediated interactions between semiconductor qubits
The realization of a coherent interface between distant charge or spin qubits
in semiconductor quantum dots is an open challenge for quantum information
processing. Here we demonstrate both resonant and non-resonant photon-mediated
coherent interactions between double quantum dot charge qubits separated by
several tens of micrometers. We present clear spectroscopic evidence of the
collective enhancement of the resonant coupling of two qubits. With both qubits
detuned from the resonator we observe exchange coupling between the qubits
mediated by virtual photons. In both instances pronounced bright and dark
states governed by the symmetry of the qubit-field interaction are found. Our
observations are in excellent quantitative agreement with master-equation
simulations. The extracted two-qubit coupling strengths significantly exceed
the linewidths of the combined resonator-qubit system. This indicates that this
approach is viable for creating photon-mediated two-qubit gates in quantum dot
based systems.Comment: 14 pages, 10 figures and 6 table
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