336 research outputs found
Probing dynamics of an electron-spin ensemble via a superconducting resonator
We study spin relaxation and diffusion in an electron-spin ensemble of
nitrogen impurities in diamond at low temperature (0.25-1.2 K) and polarizing
magnetic field (80-300 mT). Measurements exploit mode- and
temperature-dependent coupling of hyperfine-split sub-ensembles to the
resonator. Temperature-independent spin linewidth and relaxation time suggest
that spin diffusion limits spin relaxation. Depolarization of one sub-ensemble
by resonant pumping of another indicates fast cross-relaxation compared to spin
diffusion, with implications on use of sub-ensembles as independent quantum
memories.Comment: 5 pages, 5 figures, and Supplementary Information (2 figures
Modeling and Testing Superconducting Artificial CPW Lines Suitable for Parametric Amplification
Achieving amplification with high gain and quantum-limited noise is a
difficult problem to solve. Parametric amplification using a superconducting
transmission line with high kinetic inductance is a promising technology not
only to solve this problem but also adding several benefits. When compared with
other technologies, they have the potential of improving power saturation,
achieving larger fractional bandwidths and operating at higher frequencies. In
this type of amplifiers, selecting the proper transmission line is a key
element in their design. Given current fabrication limitations, traditional
lines such as coplanar waveguides (CPW), are not ideal for this purpose since
it is difficult to make them with the proper characteristic impedance for good
matching and slow-enough phase velocity for making them more compact.
Capacitively-loaded lines, also known as artificial lines, are a good solution
to this problem. However, few design rules or models have been presented to
guide their accurate design. This fact is even more crucial considering that
they are usually fabricated in the form of Floquet lines that have to be
designed carefully to suppress undesired harmonics appearing in the parametric
process. In this article we present, firstly, a new modelling strategy, based
on the use of electromagnetic-simulation software, and, secondly, a
first-principles model that facilitate and speed the design of CPW artificial
lines and of Floquet lines made out of them. Then, we present comparisons with
experimental results that demonstrate their accuracy. Finally, the theoretical
model allows to predict the high-frequency behaviour of the artificial lines
showing that they are good candidates for implementing parametric amplifiers
above 100 GHz.Comment: 7 pages, 11 figures, submitted to IEEE Transactions on Applied
Superconductivit
CSM-180 - An SQL Interface for the IFS/2 Knowledge-Baseserver: Release 2
A version of the IFS/2, known as the IFS/Q, has been designed to give direct support to SQL programs running on a host computer. This report gives detailed specifications of one external and two internal software and firmware interfaces which have been created for IFS/Q. Release 2 differs from Release 1 mainly in the Interface B details (see section 4). We have also tidied up the IFS/Q library procedures, which are described in a companion document - (see ref 9); for convenience this is included as Appendix B to this report
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
A microscopic theory for the generation and propagation of coherent LA
phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum
well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is
driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump
laser and is treated theoretically using the density matrix formalism. We use
realistic wurzite bandstructures taking valence-band mixing and strain-induced
piezo- electric fields into account. In addition, the many-body Coulomb
ineraction is treated in the screened time-dependent Hartree-Fock
approximation. We find that under typical experimental conditions, our
microscopic theory can be simplified and mapped onto a loaded string problem
which can be easily solved.Comment: 20 pages, 17 figure
Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots
We report on the impulsive generation of coherent optical phonons in
CdTe0.68Se0.32 nanocrystallites embedded in a glass matrix. Pump probe
experiments using femtosecond laser pulses were performed by tuning the laser
central energy to resonate with the absorption edge of the nanocrystals. We
identify two longitudinal optical phonons, one longitudinal acoustic phonon and
a fourth mode of a mixed longitudinal-transverse nature. The amplitude of the
optical phonons as a function of the laser central energy exhibits a resonance
that is well described by a model based on impulsive stimulated Raman
scattering. The phases of the coherent phonons reveal coupling between
different modes. At low power density excitations, the frequency of the optical
coherent phonons deviates from values obtained from spontaneous Raman
scattering. This behavior is ascribed to the presence of electronic impurity
states which modify the nanocrystal dielectric function and, thereby, the
frequency of the infrared-active phonons
Pointing calibration of GroundBIRD telescope using Moon observation data
Understanding telescope pointing (i.e., line of sight) is important for
observing the cosmic microwave background (CMB) and astronomical objects. The
Moon is a candidate astronomical source for pointing calibration. Although the
visible size of the Moon (\ang{;30}) is larger than that of the planets, we
can frequently observe the Moon once a month with a high signal-to-noise ratio.
We developed a method for performing pointing calibration using observational
data from the Moon. We considered the tilts of the telescope axes as well as
the encoder and collimation offsets for pointing calibration. In addition, we
evaluated the effects of the nonuniformity of the brightness temperature of the
Moon, which is a dominant systematic error. As a result, we successfully
achieved a pointing accuracy of \ang{;3.3}. This is one order of magnitude
smaller than an angular resolution of \ang{;36}. This level of accuracy
competes with past achievements in other ground-based CMB experiments using
observational data from the planets.Comment: 18 pages, 17 figures, 3 table
Superconducting Coplanar Waveguide Filters for Submillimeter Wave On-Chip Filterbank Spectrometers
We show the first experimental results which prove that superconducting NbTiN coplanar-waveguide resonators can achieve a loaded Q factor in excess of 800 in the 350 GHz band. These resonators can be used as narrow band pass filters for on-chip filter bank spectrometers for astronomy. Moreover, the low-loss coplanar waveguide technology provides an interesting alternative to microstrip lines for constructing large scale submillimeter wave electronics in general
- …