62 research outputs found
Measurement of non-Gaussian shot noise: influence of the environment
We present the first measurements of the third moment of the voltage
fluctuations in a conductor. This technique can provide new and complementary
information on the electronic transport in conducting systems. The measurement
was performed on non-superconducting tunnel junctions as a function of voltage
bias, for various temperatures and bandwidths up to 1GHz. The data demonstrate
the significant effect of the electromagnetic environment of the sample.Comment: 13 pages, for the SPIE International Symposium on Fluctuations and
Noise, Maspalomas, Gran Canaria, Spain (May 2004
Dispersive Photon Blockade in a Superconducting Circuit
Mediated photon-photon interactions are realized in a superconducting
coplanar waveguide cavity coupled to a superconducting charge qubit. These
non-resonant interactions blockade the transmission of photons through the
cavity. This so-called dispersive photon blockade is characterized by measuring
the total transmitted power while varying the energy spectrum of the photons
incident on the cavity. A staircase with four distinct steps is observed and
can be understood in an analogy with electron transport and the Coulomb
blockade in quantum dots. This work differs from previous efforts in that the
cavity-qubit excitations retain a photonic nature rather than a hybridization
of qubit and photon and provides the needed tolerance to disorder for future
condensed matter experiments.Comment: 4 pages, 3 figure
Comparison of Coulomb Blockade Thermometers with the International Temperature Scale PLTS-2000
The operation of the primary Coulomb blockade thermometer (CBT) is based on a
measurement of bias voltage dependent conductance of arrays of tunnel junctions
between normal metal electrodes. Here we report on a comparison of a CBT with a
high accuracy realization of the PLTS-2000 temperature scale in the range from
0.008 K to 0.65 K. An overall agreement of about 1% was found for temperatures
above 0.25 K. For lower temperatures increasing differences are caused by
thermalization problems which are accounted for by numerical calculations based
on electron-phonon decoupling.Comment: 6 pages, 5 figure
Primary thermometry in the intermediate Coulomb blockade regime
We investigate Coulomb blockade thermometers (CBT) in an intermediate
temperature regime, where measurements with enhanced accuracy are possible due
to the increased magnitude of the differential conductance dip. Previous
theoretical results show that corrections to the half width and to the depth of
the measured conductance dip of a sensor are needed, when leaving the regime of
weak Coulomb blockade towards lower temperatures. In the present work, we
demonstrate experimentally that the temperature range of a CBT sensor can be
extended by employing these corrections without compromising the primary nature
or the accuracy of the thermometer.Comment: 8 pages, 4 figure
Pressure broadening in the 2v_3 band of methane and its implication on atmospheric retrievals
N_2-broadened half widths and pressure shifts were obtained for transitions in the 2ν_3 methane band. Laboratory measurements recorded at 0.011 cm^(−1) resolution with a Bruker 120 HR Fouriertransform spectrometer were analysed from 5860 to 6185 cm^(−1). A 140 cm gas cell was filled with methane at room temperature and N_2 as foreign gas at pressures ranging from 125 to 900 hPa. A multispectrum nonlinear constrained least squares approach based on Optimal Estimation was applied to derive the spectroscopic parameters by simultaneously fitting laboratory spectra at different ambient pressures assuming a Voigt line-shape. At room temperature, the half widths ranged between 0.030 and 0.071 cm^(−1) atm^(−1), and the pressure shifts varied from –0.002 to –0.025 cm^(−1) atm^(−1) for transitions up to J"=10. Especially for higher rotational levels, we find systematically narrower lines than HITRAN predicts. The Q and R branch of the new set of spectroscopic parameters is further tested with ground based direct sun Fourier transform infrared (FTIR) measurements where systematic fit residuals reduce by about a factor of 3–4. We report the implication of those differences on atmospheric methane measurements using high-resolution ground based FTIR measurements as well as low-resolution spectra from the SCanning Imaging Absorption SpectroMeter for Atmospheric ChartographY (SCIAMACHY) instrument onboard ENVISAT. We find that for SCIAMACHY, a latitudinal and seasonally varying bias of about 1% can be introduced by erroneous broadening parameters
Methane spectroscopy in the near infrared and its implication on atmospheric retrievals
International audienceN2-broadened half widths and pressure shifts were obtained for transitions in the Q and R branches of the 2?3 methane band. Laboratory measurements were done from 5985 to 6185 cm?1 using spectra recorded at 0.011 cm?1 resolution with a Bruker 120 HR Fourier transform spectrometer. A 140 cm gas cell was filled with methane at room temperature and N2 as foreign gas at pressures ranging from 125 to 900 hPa. A multispectrum nonlinear constrained least squares approach based on Optimal Estimation was applied to derive the spectroscopic parameters by simultaneously fitting laboratory spectra at different ambient pressures assuming a Voigt line-shape. At room temperature, the half widths ranged between 0.030 and 0.071 cm?1 atm?1, and the pressure shifts varied from ?0.002 to ?0.025 cm?1 atm?1 for transitions up to J"=10. Especially for higher rotational levels, we find systematically narrower lines than HITRAN predicts. The new set of spectroscopic parameters is further tested with ground based direct sun FTIR measurements where fit residuals reduce by about a factor of 3?4. We report the implication of those differences on atmospheric methane measurements using high-resolution ground based FTIR measurements as well as low-resolution spectra from the SCIAMACHY instrument onboard ENVISAT. We find that for SCIAMACHY, a latitudinal and seasonally varying bias of about 1% can be introduced by erroneous broadening parameters
Gossamer roadmap technology reference study for a solar polar mission
A technology reference study for a solar polar mission is presented. The study uses novel analytical methods to quantify the mission design space including the required sail performance to achieve a given solar polar observation angle within a given timeframe and thus to derive mass allocations for the remaining spacecraft sub-systems, that is excluding the solar sail sub-system. A parametric, bottom-up, system mass budget analysis is then used to establish the required sail technology to deliver a range of science payloads, and to establish where such payloads can be delivered to within a given timeframe. It is found that a solar polar mission requires a solar sail of side-length 100 – 125 m to deliver a ‘sufficient value’ minimum science payload, and that a 2. 5μm sail film substrate is typically required, however the design is much less sensitive to the boom specific mass
Phase preserving amplification near the quantum limit with a Josephson Ring Modulator
Recent progress in solid state quantum information processing has stimulated
the search for ultra-low-noise amplifiers and frequency converters in the
microwave frequency range, which could attain the ultimate limit imposed by
quantum mechanics. In this article, we report the first realization of an
intrinsically phase-preserving, non-degenerate superconducting parametric
amplifier, a so far missing component. It is based on the Josephson ring
modulator, which consists of four junctions in a Wheatstone bridge
configuration. The device symmetry greatly enhances the purity of the
amplification process and simplifies both its operation and analysis. The
measured characteristics of the amplifier in terms of gain and bandwidth are in
good agreement with analytical predictions. Using a newly developed noise
source, we also show that our device operates within a factor of three of the
quantum limit. This development opens new applications in the area of quantum
analog signal processing
Observation of the Dynamical Casimir Effect in a Superconducting Circuit
One of the most surprising predictions of modern quantum theory is that the
vacuum of space is not empty. In fact, quantum theory predicts that it teems
with virtual particles flitting in and out of existence. While initially a
curiosity, it was quickly realized that these vacuum fluctuations had
measurable consequences, for instance producing the Lamb shift of atomic
spectra and modifying the magnetic moment for the electron. This type of
renormalization due to vacuum fluctuations is now central to our understanding
of nature. However, these effects provide indirect evidence for the existence
of vacuum fluctuations. From early on, it was discussed if it might instead be
possible to more directly observe the virtual particles that compose the
quantum vacuum. 40 years ago, Moore suggested that a mirror undergoing
relativistic motion could convert virtual photons into directly observable real
photons. This effect was later named the dynamical Casimir effect (DCE). Using
a superconducting circuit, we have observed the DCE for the first time. The
circuit consists of a coplanar transmission line with an electrical length that
can be changed at a few percent of the speed of light. The length is changed by
modulating the inductance of a superconducting quantum interference device
(SQUID) at high frequencies (~11 GHz). In addition to observing the creation of
real photons, we observe two-mode squeezing of the emitted radiation, which is
a signature of the quantum character of the generation process.Comment: 12 pages, 3 figure
Non-equilibrium coherence dynamics in one-dimensional Bose gases
Low-dimensional systems are beautiful examples of many-body quantum physics.
For one-dimensional systems the Luttinger liquid approach provides insight into
universal properties. Much is known of the equilibrium state, both in the
weakly and strongly interacting regime. However, it remains a challenge to
probe the dynamics by which this equilibrium state is reached. Here we present
a direct experimental study of the coherence dynamics in both isolated and
coupled degenerate 1d Bose gases. Dynamic splitting is used to create two 1d
systems in a phase coherent state. The time evolution of the coherence is
revealed in local phase shifts of the subsequently observed interference
patterns. Completely isolated 1d Bose gases are observed to exhibit a universal
sub-exponential coherence decay in excellent agreement with recent predictions
by Burkov et al. [Phys. Rev. Lett. 98, 200404 (2007)]. For two coupled 1d Bose
gases the coherence factor is observed to approach a non-zero equilibrium value
as predicted by a Bogoliubov approach. This coupled-system decay to finite
coherence is the matter wave equivalent of phase locking two lasers by
injection. The non-equilibrium dynamics of superfluids plays an important role
in a wide range of physical systems, such as superconductors, quantum-Hall
systems, superfluid Helium, and spin systems. Our experiments studying
coherence dynamics show that 1d Bose gases are ideally suited for investigating
this class of phenomena.Comment: to appear in natur
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