570 research outputs found
Primary thermometry triad at 6 mK in mesoscopic circuits
Quantum physics emerge and develop as temperature is reduced. Although
mesoscopic electrical circuits constitute an outstanding platform to explore
quantum behavior, the challenge in cooling the electrons impedes their
potential. The strong coupling of such micrometer-scale devices with the
measurement lines, combined with the weak coupling to the substrate, makes them
extremely difficult to thermalize below 10 mK and imposes in-situ thermometers.
Here we demonstrate electronic quantum transport at 6 mK in micrometer-scale
mesoscopic circuits. The thermometry methods are established by the comparison
of three in-situ primary thermometers, each involving a different underlying
physics. The employed combination of quantum shot noise, quantum back-action of
a resistive circuit and conductance oscillations of a single-electron
transistor covers a remarkably broad spectrum of mesoscopic phenomena. The
experiment, performed in vacuum using a standard cryogen-free dilution
refrigerator, paves the way toward the sub-millikelvin range with additional
thermalization and refrigeration techniques.Comment: Article and Supplementar
Circuit Quantum Simulation of a Tomonaga-Luttinger Liquid with an Impurity
The Tomonaga-Luttinger liquid (TLL) concept is believed to generically
describe the strongly-correlated physics of one-dimensional systems at low
temperatures. A hallmark signature in 1D conductors is the quantum phase
transition between metallic and insulating states induced by a single impurity.
However, this transition impedes experimental explorations of real-world TLLs.
Furthermore, its theoretical treatment, explaining the universal energy
rescaling of the conductance at low temperatures, has so far been achieved
exactly only for specific interaction strengths. Quantum simulation can provide
a powerful workaround. Here, a hybrid metal-semiconductor dissipative quantum
circuit is shown to implement the analogue of a TLL of adjustable electronic
interactions comprising a single, fully tunable scattering impurity.
Measurements reveal the renormalization group `beta-function' for the
conductance that completely determines the TLL universal crossover to an
insulating state upon cooling. Moreover, the characteristic scaling energy
locating at a given temperature the position within this conductance
renormalization flow is established over nine decades versus circuit
parameters, and the out-of-equilibrium regime is explored. With the quantum
simulator quality demonstrated from the precise parameter-free validation of
existing and novel TLL predictions, quantum simulation is achieved in a strong
sense, by elucidating interaction regimes which resist theoretical solutions.Comment: To be published in Phys. Rev.
Loss and decoherence at the quantum Hall - superconductor interface
High quality type-II superconducting contacts have recently been developed to
a variety of 2D systems, allowing one to explore the superconducting proximity
in the quantum Hall (QH) regime. Inducing superconducting correlations into a
chiral system has long been viewed as a route for creating exotic topological
states and excitations. However, it appears that before these exciting
predictions could be realized, one should develop a better understanding of the
limitations imposed by the physics of real materials. Here, we perform a
systematic study of Andreev conversion at the interface between a
superconductor and graphene in the QH regime. We find that the probability of
Andreev conversion of electrons to holes follows an unexpected but clear trend:
the dependencies on temperature and magnetic field are nearly decoupled. We
discuss these trends and the role of the superconducting vortices, whose normal
cores could both absorb and dephase the individual electrons in a QH edge. Our
study may pave the road to engineering future generation of hybrid devices for
exploiting superconductivity proximity in chiral channels
Graphene-based quantum Hall interferometer with self-aligned side gates
The vanishing band gap of graphene has long presented challenges for
fabricating high-quality quantum point contacts (QPCs) -- the partially
transparent p-n interfaces introduced by conventional split-gates tend to short
the QPC. This complication has hindered the fabrication of graphene quantum
Hall Fabry-P\'erot interferometers, until recent advances have allowed
split-gate QPCs to operate utilizing the highly resistive state. Here,
we present a simple recipe to fabricate QPCs by etching a narrow trench in the
graphene sheet to separate the conducting channel from self-aligned graphene
side gates. We demonstrate operation of the individual QPCs in the quantum Hall
regime, and further utilize these QPCs to create and study a quantum Hall
interferometer
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