1,388 research outputs found
Implementation of a Transmon Qubit Using Superconducting Granular Aluminum
The high kinetic inductance offered by granular aluminum (grAl) has recently been employed for linear inductors in superconducting high-impedance qubits and kinetic inductance detectors. Because of its large critical current density compared to typical Josephson junctions, its resilience to external magnetic fields, and its low dissipation, grAl may also provide a robust source of nonlinearity for strongly driven quantum circuits, topological superconductivity, and hybrid systems. Having said that, can the grAl nonlinearity be sufficient to build a qubit? Here we show that a small grAl volume (10×200×500 nm) shunted by a thin film aluminum capacitor results in a microwave oscillator with anharmonicity α two orders of magnitude larger than its spectral linewidth Γ, effectively forming a transmon qubit. With increasing drive power, we observe several multiphoton transitions starting from the ground state, from which we extract α=2×4.48 MHz. Resonance fluorescence measurements of the |0⟩→|1⟩ transition yield an intrinsic qubit linewidth γ=2×10 kHz, corresponding to a lifetime of 16 μs, as confirmed by pulsed time-domain measurements. This linewidth remains below 2×150 kHz for in-plane magnetic fields up to ∼70 mT
155-day Periodicity in Solar Cycles 3 and 4
The near 155 days solar periodicity, so called Rieger periodicity, was first
detected in solar flares data and later confirmed with other important solar
indices. Unfortunately, a comprehensive analysis on the occurrence of this
periodicity during previous centuries can be further complicated due to the
poor quality of the sunspot number time-series. We try to detect the Rieger
periodicity during the solar cycles 3 and 4 using information on aurorae
observed at mid and low latitudes. We use two recently discovered aurora
datasets, observed in the last quarter of the 18th century from UK and Spain.
Besides simple histograms of time between consecutive events we analyse monthly
series of number of aurorae observed using different spectral analysis (MTM and
Wavelets). The histograms show the probable presence of Rieger periodicity
during cycles 3 and 4. However different spectral analysis applied has only
confirmed undoubtedly this hypothesis for solar cycle 3.Comment: 13 pages, 6 figures, to appear in New Astronom
Quantum Nondemolition Dispersive Readout of a Superconducting Artificial Atom Using Large Photon Numbers
Reading out the state of superconducting artificial atoms typically relies on dispersive coupling to a readout resonator. For a given system noise temperature, increasing the circulating photon number in the resonator enables a shorter measurement time and is therefore expected to reduce readout errors caused by spontaneous atom transitions. However, increasing is generally observed to also monotonously increase these transition rates. Here we present a fluxonium artificial atom in which, despite the fact that the measured transition rates show nonmonotonous fluctuations within a factor of 6, for photon numbers up to ≈200, the signal-to-noise ratio continuously improves with increasing . Even without the use of a parametric amplifier, at =74, we achieve fidelities of 99% and 93% for feedback-assisted ground and excited state preparations, respectively. At higher , leakage outside the qubit computational space can no longer be neglected and it limits the fidelity of quantum state preparation
Quantum non-demolition dispersive readout of a superconducting artificial atom using large photon numbers
Reading out the state of superconducting artificial atoms typically relies on
dispersive coupling to a readout resonator. For a given system noise
temperature, increasing the circulating photon number in the
resonator enables a shorter measurement time and is therefore expected to
reduce readout errors caused by spontaneous atom transitions. However,
increasing is generally observed to also increase these transition
rates. Here we present a fluxonium artificial atom in which we measure an
overall flat dependence of the transition rates between its first two states as
a function of , up to . Despite the fact that we
observe the expected decrease of the dispersive shift with increasing readout
power, the signal-to-noise ratio continuously improves with increasing
. Even without the use of a parametric amplifier, at , we
measure fidelities of 99% and 93% for feedback-assisted ground and excited
state preparation, respectively.Comment: typos corrected, added figure at p.10 (section IV of the Supplemental
Material), added reference
A field study of data analysis exercises in a bachelor physics course using the internet platform VISPA
Bachelor physics lectures on particle physics and astrophysics were
complemented by exercises related to data analysis and data interpretation at
the RWTH Aachen University recently. The students performed these exercises
using the internet platform VISPA, which provides a development environment for
physics data analyses. We describe the platform and its application within the
physics course, and present the results of a student survey. The students
acceptance of the learning project was positive. The level of acceptance was
related to their individual preference for learning with a computer.
Furthermore, students with good programming skills favor working individually,
while students who attribute themselves having low programming abilities favor
working in teams. The students appreciated approaching actual research through
the data analysis tasks.Comment: 21 pages, 8 figures, 1 table, for the internet platform VISPA see
http://vispa.physik.rwth-aachen.d
Multi-wavelength analysis of high energy electrons in solar flares: a case study of August 20, 2002 flare
A multi-wavelength spatial and temporal analysis of solar high energy
electrons is conducted using the August 20, 2002 flare of an unusually flat
(gamma=1.8) hard X-ray spectrum. The flare is studied using RHESSI, Halpha,
radio, TRACE, and MDI observations with advanced methods and techniques never
previously applied in the solar flare context. A new method to account for
X-ray Compton backscattering in the photosphere (photospheric albedo) has been
used to deduce the primary X-ray flare spectra. The mean electron flux
distribution has been analysed using both forward fitting and model independent
inversion methods of spectral analysis. We show that the contribution of the
photospheric albedo to the photon spectrum modifies the calculated mean
electron flux distribution, mainly at energies below 100 keV. The positions of
the Halpha emission and hard X-ray sources with respect to the current-free
extrapolation of the MDI photospheric magnetic field and the characteristics of
the radio emission provide evidence of the closed geometry of the magnetic
field structure and the flare process in low altitude magnetic loops. In
agreement with the predictions of some solar flare models, the hard X-ray
sources are located on the external edges of the Halpha emission and show
chromospheric plasma heated by the non-thermal electrons. The fast changes of
Halpha intensities are located not only inside the hard X-ray sources, as
expected if they are the signatures of the chromospheric response to the
electron bombardment, but also away from them.Comment: 26 pages, 9 figures, accepted to Solar Physic
A quantum Szilard engine for two-level systems coupled to a qubit
The innate complexity of solid state physics exposes superconducting quantum
circuits to interactions with uncontrolled degrees of freedom degrading their
coherence. By using a simple stabilization sequence we show that a
superconducting fluxonium qubit is coupled to a two-level system (TLS)
environment of unknown origin, with a relatively long energy relaxation time
exceeding . Implementing a quantum Szilard engine with an active
feedback control loop allows us to decide whether the qubit heats or cools its
TLS environment. The TLSs can be cooled down resulting in a four times lower
qubit population, or they can be heated to manifest themselves as a negative
temperature environment corresponding to a qubit population of .
We show that the TLSs and the qubit are each other's dominant loss mechanism
and that the qubit relaxation is independent of the TLS populations.
Understanding and mitigating TLS environments is therefore not only crucial to
improve qubit lifetimes but also to avoid non-Markovian qubit dynamics
Implementation of a transmon qubit using superconducting granular aluminum
The high kinetic inductance offered by granular aluminum (grAl) has recently
been employed for linear inductors in superconducting high-impedance qubits and
kinetic inductance detectors. Due to its large critical current density
compared to typical Josephson junctions, its resilience to external magnetic
fields, and its low dissipation, grAl may also provide a robust source of
non-linearity for strongly driven quantum circuits, topological
superconductivity, and hybrid systems. Having said that, can the grAl
non-linearity be sufficient to build a qubit? Here we show that a small grAl
volume () shunted by a thin film
aluminum capacitor results in a microwave oscillator with anharmonicity
two orders of magnitude larger than its spectral linewidth
, effectively forming a transmon qubit. With increasing drive
power, we observe several multi-photon transitions starting from the ground
state, from which we extract .
Resonance fluorescence measurements of the transition
yield an intrinsic qubit linewidth ,
corresponding to a lifetime of . This linewidth remains
below for in-plane magnetic fields up to
.Comment: 4 + 8 Pages and 4 + 8 Figure
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