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High-Order Dual-Port Quasi-Absorptive Microstrip Coupled-Line Bandpass Filters
In this article, we present the first demonstration of distributed and symmetrical all-band quasi-absorptive filters that can be designed to arbitrarily high orders. The proposed quasi-absorptive filter consists of a bandpass section (reflective-type coupled-line filter) and absorptive sections (a matched resistor in series with a shorted quarter-wavelength transmission line). Through a detailed analysis, we show that the absorptive sections not only eliminate out-of-band reflections but also determine the passband bandwidth (BW). As such, the bandpass section mainly determines the out-of-band roll-off and the order of the filter can be arbitrarily increased without affecting the filter BW by cascading more bandpass sections. A set of 2.45-GHz one-, two-, and three-pole quasi-absorptive microstrip bandpass filters are designed and measured. The filters show simultaneous input and output absorption across both the passband and the stopband. Measurement results agree very well with the simulation and validate the proposed design concept
Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits
The ability to generate particles from the quantum vacuum is one of the most
profound consequences of Heisenberg's uncertainty principle. Although the
significance of vacuum fluctuations can be seen throughout physics, the
experimental realization of vacuum amplification effects has until now been
limited to a few cases. Superconducting circuit devices, driven by the goal to
achieve a viable quantum computer, have been used in the experimental
demonstration of the dynamical Casimir effect, and may soon be able to realize
the elusive verification of analogue Hawking radiation. This article describes
several mechanisms for generating photons from the quantum vacuum and
emphasizes their connection to the well-known parametric amplifier from quantum
optics. Discussed in detail is the possible realization of each mechanism, or
its analogue, in superconducting circuit systems. The ability to selectively
engineer these circuit devices highlights the relationship between the various
amplification mechanisms.Comment: 27 pages, 10 figures, version published in Rev. Mod. Phys. as a
Colloquiu
Small Size Dual-band Bandpass Filters with Multiconductor Transmission Lines and Shunt Open Stubs
A dual-band bandpass filter consisting of multiconductor transmission lines (MTL) and shunt stubs has been designed. The used topology, based on the interconnection of two identical MTL and a shunt open stub, has a frequency response that can be modelled by using the generalized Chebyshev functions. A prototype of a 4 fingers-MTL is manufactured and measured and a good agreement between analytical and measured results is obtained. Furthermore, it is easy to get a design criterion that enables getting good responses varying just a few parameters.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech
Digital-Analog Quantum Simulations with Superconducting Circuits
Quantum simulations consist in the intentional reproduction of physical or
unphysical models into another more controllable quantum system. Beyond
establishing communication vessels between unconnected fields, they promise to
solve complex problems which may be considered as intractable for classical
computers. From a historic perspective, two independent approaches have been
pursued, namely, digital and analog quantum simulations. The former usually
provide universality and flexibility, while the latter allows for better
scalability. Here, we review recent literature merging both paradigms in the
context of superconducting circuits, yielding: digital-analog quantum
simulations. In this manner, we aim at getting the best of both approaches in
the most advanced quantum platform involving superconducting qubits and
microwave transmission lines. The discussed merge of quantum simulation
concepts, digital and analog, may open the possibility in the near future for
outperforming classical computers in relevant problems, enabling the reach of a
quantum advantage.Comment: Review article, 26 pages, 4 figure
Digital quantum simulation of spin models with circuit quantum electrodynamics
Systems of interacting quantum spins show a rich spectrum of quantum phases
and display interesting many-body dynamics. Computing characteristics of even
small systems on conventional computers poses significant challenges. A quantum
simulator has the potential to outperform standard computers in calculating the
evolution of complex quantum systems. Here, we perform a digital quantum
simulation of the paradigmatic Heisenberg and Ising interacting spin models
using a two transmon-qubit circuit quantum electrodynamics setup. We make use
of the exchange interaction naturally present in the simulator to construct a
digital decomposition of the model-specific evolution and extract its full
dynamics. This approach is universal and efficient, employing only resources
which are polynomial in the number of spins and indicates a path towards the
controlled simulation of general spin dynamics in superconducting qubit
platforms.Comment: 12 pages, 9 figure
Breaking time-reversal symmetry with a superconducting flux capacitor
We present the design of a passive, on-chip microwave circulator based on a
ring of superconducting tunnel junctions. We investigate two distinct physical
realisations, based on either Josephson junctions (JJ) or quantum phase slip
elements (QPS), with microwave ports coupled either capacitively (JJ) or
inductively (QPS) to the ring structure. A constant bias applied to the center
of the ring provides the symmetry breaking (effective) magnetic field, and no
microwave or rf bias is required. We find that this design offers high
isolation even when taking into account fabrication imperfections and
environmentally induced bias perturbations and find a bandwidth in excess of
500 MHz for realistic device parameters.Comment: 10 pages, 11 figures, including supplementary material - published as
"Passive on-chip, superconducting circulator using rings of tunnel junctions
Superconducting Nanowires as Nonlinear Inductive Elements for Qubits
We report microwave transmission measurements of superconducting Fabry-Perot
resonators (SFPR), having a superconducting nanowire placed at a supercurrent
antinode. As the plasma oscillation is excited, the supercurrent is forced to
flow through the nanowire. The microwave transmission of the resonator-nanowire
device shows a nonlinear resonance behavior, significantly dependent on the
amplitude of the supercurrent oscillation. We show that such
amplitude-dependent response is due to the nonlinearity of the current-phase
relationship (CPR) of the nanowire. The results are explained within a
nonlinear oscillator model of the Duffing oscillator, in which the nanowire
acts as a purely inductive element, in the limit of low temperatures and low
amplitudes. The low quality factor sample exhibits a "crater" at the resonance
peak at higher driving power, which is due to dissipation. We observe a
hysteretic bifurcation behavior of the transmission response to frequency sweep
in a sample with a higher quality factor. The Duffing model is used to explain
the Duffing bistability diagram. We also propose a concept of a nanowire-based
qubit that relies on the current dependence of the kinetic inductance of a
superconducting nanowire.Comment: 28 pages, 7 figure
Beyond Strong Coupling in a Massively Multimode Cavity
The study of light-matter interaction has seen a resurgence in recent years,
stimulated by highly controllable, precise, and modular experiments in cavity
quantum electrodynamics (QED). The achievement of strong coupling, where the
coupling between a single atom and fundamental cavity mode exceeds the decay
rates, was a major milestone that opened the doors to a multitude of new
investigations. Here we introduce multimode strong coupling (MMSC), where the
coupling is comparable to the free spectral range (FSR) of the cavity, i.e. the
rate at which a qubit can absorb a photon from the cavity is comparable to the
round trip transit rate of a photon in the cavity. We realize, via the circuit
QED architecture, the first experiment accessing the MMSC regime, and report
remarkably widespread and structured resonance fluorescence, whose origin
extends beyond cavity enhancement of sidebands. Our results capture complex
multimode, multiphoton processes, and the emergence of ultranarrow linewidths.
Beyond the novel phenomena presented here, MMSC opens a major new direction in
the exploration of light-matter interactions.Comment: 14 pages, 11 figures. References added, typos correcte
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