3,531 research outputs found
Transmission lines and resonators based on quantum Hall plasmonics: electromagnetic field, attenuation and coupling to qubits
Quantum Hall edge states have some characteristic features that can prove
useful to measure and control solid state qubits. For example, their high
voltage to current ratio and their dissipationless nature can be exploited to
manufacture low-loss microwave transmission lines and resonators with a
characteristic impedance of the order of the quantum of resistance . The high value of the impedance guarantees that the
voltage per photon is high and for this reason high impedance resonators can be
exploited to obtain larger values of coupling to systems with a small charge
dipole, e.g. spin qubits. In this paper, we provide a microscopic analysis of
the physics of quantum Hall effect devices capacitively coupled to external
electrodes. The electrical current in these devices is carried by edge
magnetoplasmonic excitations and by using a semiclassical model, valid for a
wide range of quantum Hall materials, we discuss the spatial profile of the
electromagnetic field in a variety of situations of interest. Also, we perform
a numerical analysis to estimate the lifetime of these excitations and, from
the numerics, we extrapolate a simple fitting formula which quantifies the
factor in quantum Hall resonators. We then explore the possibility of reaching
the strong photon-qubit coupling regime, where the strength of the interaction
is higher than the losses in the system. We compute the Coulomb coupling
strength between the edge magnetoplasmons and singlet-triplet qubits, and we
obtain values of the coupling parameter of the order ;
comparing these values to the estimated attenuation in the resonator, we find
that for realistic qubit designs the coupling can indeed be strong
Self impedance matched Hall-effect gyrators and circulators
We present a model study of an alternative implementation of a two-port
Hall-effect microwave gyrator. Our set-up involves three electrodes, one of
which acts as a common ground for the others. Based on the capacitive-coupling
model of Viola and DiVincenzo, we analyze the performance of the device and we
predict that ideal gyration can be achieved at specific frequencies.
Interestingly, the impedance of the three-terminal gyrator can be made
arbitrarily small for certain coupling strengths, so that no auxiliary
impedance matching is required. Although the bandwidth of the device shrinks as
the impedance decreases, it can be improved by reducing the magnetic field; it
can be realistically increased up to at
by working at filling factor . We examine also the effects of the
parasitic capacitive coupling between electrodes and we find that, although in
general they strongly influence the response of device, their effect is
negligible at low impedance. Finally, we analyze an interferometric
implementation of a circulator, which incorporates the gyrator in a
Mach-Zender-like construction. Perfect circulation in both directions can be
achieved, depending on frequency and on the details of the interferometer
A model study of present-day Hall-effect circulators
Stimulated by the recent implementation of a three-port Hall-effect microwave
circulator of Mahoney et al. (MEA), we present model studies of the performance
of this device. Our calculations are based on the capacitive-coupling model of
Viola and DiVincenzo (VD). Based on conductance data from a typical Hall-bar
device obtained from a two-dimensional electron gas (2DEG) in a magnetic field,
we numerically solve the coupled field-circuit equations to calculate the
expected performance of the circulator, as determined by the parameters of
the device when coupled to 50 ports, as a function of frequency and
magnetic field. Above magnetic fields of 1.5T, for which a typical 2DEG enters
the quantum Hall regime (corresponding to a Landau-level filling fraction
of 20), the Hall angle always
remains close to , and the parameters are close to the analytic
predictions of VD for . As anticipated by VD, MEA find the
device to have rather high (k) impedance, and thus to be extremely
mismatched to , requiring the use of impedance matching. We
incorporate the lumped matching circuits of MEA in our modeling and confirm
that they can produce excellent circulation, although confined to a very small
bandwidth. We predict that this bandwidth is significantly improved by working
at lower magnetic field when the Landau index is high, e.g. , and the
impedance mismatch is correspondingly less extreme. Our modeling also confirms
the observation of MEA that parasitic port-to-port capacitance can produce very
interesting countercirculation effects
A digital control system for high level acoustic noise generation
As part of the modernization of the Acoustic Test Facility at Lockheed Missiles and Space Company, Sunnyvale, a digital acoustic control system was designed and built. The requirements imposed by Lockheed on the control system and the degree to which those requirements were met are discussed. Acceptance test results as well as some of the features of the digital control system not found in traditional manual control systems are discussed
Transmission Lines and Meta-Materials based on Quantum Hall Plasmonics
The characteristic impedance of a microwave transmission line is typically
constrained to a value = 50 , in-part because of the low
impedance of free space and the limited range of permittivity and permeability
realizable with conventional materials. Here we suggest the possibility of
constructing high-impedance transmission lines by exploiting the plasmonic
response of edge states associated with the quantum Hall effect in gated
devices. We analyze various implementations of quantum Hall transmission lines
based on distributed networks and lumped-element circuits, including a detailed
account of parasitic capacitance and Coulomb drag effects, which can modify
device performance. We additionally conceive of a meta-material structure
comprising arrays of quantum Hall droplets and analyze its unusual properties.
The realization of such structures holds promise for efficiently wiring-up
quantum circuits on chip, as well as engineering strong coupling between
semiconductor qubits and microwave photons
Three-dimensional instabilities of a stratified cylinder wake
International audienceThis paper describes experimentally, numerically and theoretically how the three-dimensional instabilities of a cylinder wake are modified by the presence of a linear density stratification. The first part is focused on the case of a cylinder with a small tilt angle between the cylinder's axis and the vertical. The classical mode A well-known for a homogeneous fluid is still present. It is more unstable for moderate stratifications but it is stabilized by a strong stratification. The second part treats the case of a moderate tilt angle. For moderate stratifications, a new unstable mode appears, mode S, characterized by undulated layers of strong density gradients and axial flow. These structures correspond to KelvinâHelmholtz billows created by the strong shear present in the critical layer of each tilted von KĂĄrmĂĄn vortex. The last two parts deal with the case of a strongly tilted cylinder. For a weak stratification, an instability (mode RT) appears far from the cylinder, due to the overturning of the isopycnals by the von KĂĄrmĂĄn vortices. For a strong stratification, a short wavelength unstable mode (mode L) appears, even in the absence of von KĂĄrmĂĄn vortices. It is probably due to the strong shear created by the lee waves upstream of a secondary recirculation bubble. A map of the four different unstable modes is established in terms of the three parameters of the study: the Reynolds number, the Froude number (characterizing the stratification) and the tilt angle
A collaborative engineering platform for supporting design optimisation of advanced aero engine sub-systems
- âŠ