28 research outputs found
Mode engineering with a one-dimensional superconducting metamaterial
We propose a way to control the Josephson energy of a single Josephson
junction embedded in one- dimensional superconducting metamaterial: an
inhomogeneous superconducting loop, made out of a superconducting nanowire or a
chain of Josephson junctions. The Josephson energy is renormalized by the
electromagnetic modes propagating along the loop. We study the behaviour of the
modes as well as of their frequency spectrum when the capacitance and the
inductance along the loop are spatially modulated. We show that, depending on
the amplitude of the modulation, the renormalized Josephson energy is either
larger or smaller than the one found for a homogeneous loop. Using typical
experimental parameters for Josepshon junction chains and superconducting
nanowires, we conclude that this mode-engineering can be achieved with
currently available metamaterials
Comment on "Inconsistency of the conventional theory of superconductivity" by J.E. Hirsch
J. E. Hirsch [EPL 130 (2020) 17006] claimed an inconsistency between
thermodynamics and the theory of superconductivity. We argue that he overlooked
a crucial term which determines the supercurrent dynamics and ensures energy
conservation by providing an internal energy source for the Joule heating.
Thermodynamic consistency is restored by restoring energy conservation. The
correct dynamics is given by Maxwell's equations in the superconductor.Comment: Comment (2 pages) and Supplementary Material (3 pages) in a single
file. Version 2 has corrected a confusing typo above Eq. (1
Theory of coherent quantum phase-slips in Josephson junction chains with periodic spatial modulations
We study coherent quantum phase-slips which lift the ground state degeneracy
in a Josephson junction ring, pierced by a magnetic flux of the magnitude equal
to half of a flux quantum. The quantum phase-slip amplitude is sensitive to the
normal mode structure of superconducting phase oscillations in the ring
(Mooij-Sch\"on modes). These, in turn, are affected by spatial inhomogeneities
in the ring. We analyze the case of weak periodic modulations of the system
parameters and calculate the corresponding modification of the quantum
phase-slip amplitude
A photonic crystal Josephson traveling wave parametric amplifier
An amplifier combining noise performances as close as possible to the quantum
limit with large bandwidth and high saturation power is highly desirable for
many solid state quantum technologies such as high fidelity qubit readout or
high sensitivity electron spin resonance for example. Here we introduce a new
Traveling Wave Parametric Amplifier based on Superconducting QUantum
Interference Devices. It displays a 3 GHz bandwidth, a -102 dBm 1-dB
compression point and added noise near the quantum limit. Compared to previous
state-of-the-art, it is an order of magnitude more compact, its characteristic
impedance is in-situ tunable and its fabrication process requires only two
lithography steps. The key is the engineering of a gap in the dispersion
relation of the transmission line. This is obtained using a periodic modulation
of the SQUID size, similarly to what is done with photonic crystals. Moreover,
we provide a new theoretical treatment to describe the non-trivial interplay
between non-linearity and such periodicity. Our approach provides a path to
co-integration with other quantum devices such as qubits given the low
footprint and easy fabrication of our amplifier.Comment: 6 pages, 4 figures, Appendixe
Stochastic dynamics of magnetization in a ferromagnetic nanoparticle out of equilibrium
We consider a small metallic particle (quantum dot) where ferromagnetism
arises as a consequence of Stoner instability. When the particle is connected
to electrodes, exchange of electrons between the particle and the electrodes
leads to a temperature- and bias-driven Brownian motion of the direction of the
particle magnetization. Under certain conditions this Brownian motion is
described by the stochastic Landau-Lifshitz-Gilbert equation. As an example of
its application, we calculate the frequency-dependent magnetic susceptibility
of the particle in a constant external magnetic field, which is relevant for
ferromagnetic resonance measurements.Comment: 15 pages, 6 figure
Revealing the finite-frequency response of a bosonic quantum impurity
Quantum impurities are ubiquitous in condensed matter physics and constitute
the most stripped-down realization of many-body problems. While measuring their
finite-frequency response could give access to key characteristics such as
excitations spectra or dynamical properties, this goal has remained elusive
despite over two decades of studies in nanoelectronic quantum dots. Conflicting
experimental constraints of very strong coupling and large measurement
bandwidths must be met simultaneously. We get around this problem using cQED
tools, and build a precisely characterized quantum simulator of the boundary
sine-Gordon model, a non-trivial bosonic impurity problem. We succeeded to
fully map out the finite frequency linear response of this system. Its reactive
part evidences a strong renormalisation of the nonlinearity at the boundary in
agreement with non-perturbative calculations. Its dissipative part reveals a
dramatic many-body broadening caused by multi-photon conversion. The
experimental results are matched quantitatively to a resummed diagrammatic
calculation based on a microscopically calibrated model. Furthermore, we push
the device into a regime where diagrammatic calculations break down, which
calls for more advanced theoretical tools to model many-body quantum circuits.
We also critically examine the technological limitations of cQED platforms to
reach universal scaling laws. This work opens exciting perspectives for the
future such as quantifying quantum entanglement in the vicinity of a quantum
critical point or accessing the dynamical properties of non-trivial many-body
problems.Comment: 39 pages, 14 figure
Raman spectroscopy as a versatile tool for studying the properties of graphene.
Raman spectroscopy is an integral part of graphene research. It is used to determine the number and orientation of layers, the quality and types of edge, and the effects of perturbations, such as electric and magnetic fields, strain, doping, disorder and functional groups. This, in turn, provides insight into all sp(2)-bonded carbon allotropes, because graphene is their fundamental building block. Here we review the state of the art, future directions and open questions in Raman spectroscopy of graphene. We describe essential physical processes whose importance has only recently been recognized, such as the various types of resonance at play, and the role of quantum interference. We update all basic concepts and notations, and propose a terminology that is able to describe any result in literature. We finally highlight the potential of Raman spectroscopy for layered materials other than graphene
Non-equilibrium quasiparticles in superconducting circuits: photons vs. phonons
We study the effect of non-equilibrium quasiparticles on the operation of a superconducting device (a qubit or a resonator), including heating of the quasiparticles by the device operation. Focusing on the competition between heating via low-frequency photon absorption and cooling via photon and phonon emission, we obtain a remarkably simple non-thermal stationary solution of the kinetic equation for the quasiparticle distribution function. We estimate the influence of quasiparticles on relaxation and excitation rates for transmon qubits, and relate our findings to recent experiments