178 research outputs found
Shot noise detection in hBN-based tunnel junctions
High quality Au/hBN/Au tunnel devices are fabricated using transferred
atomically thin hexagonal boron nitride as the tunneling barrier. All tunnel
junctions show tunneling resistance on the order of several
k/m. Ohmic I-V curves at small bias with no signs of
resonances indicate the sparsity of defects. Tunneling current shot noise is
measured in these devices, and the excess shot noise shows consistency with
theoretical expectations. These results show that atomically thin hBN is an
excellent tunnel barrier, especially for the study of shot noise properties,
and this can enable the study of tunneling density of states and shot noise
spectroscopy in more complex systems.Comment: 20 pages, 4 figure
Dynamics of Quantum Noise in a Tunnel Junction under ac Excitation
We report the first measurement of the \emph{dynamical response} of shot
noise (measured at frequency ) of a tunnel junction to an ac excitation
at frequency . The experiment is performed in the quantum regime,
at very low temperature T=35mK and high
frequency GHz. We observe that the noise responds in phase
with the excitation, but not adiabatically. The results are in very good
agreement with a prediction based on a new current-current correlator.Comment: Theory removed. More experimental details. One extra figur
Observation of two-mode squeezing in a traveling wave parametric amplifier
Traveling wave parametric amplifiers (TWPAs) have recently emerged as
essential tools for broadband near quantum-limited amplification. However,
their use to generate microwave quantum states still misses an experimental
demonstration. In this letter, we report operation of a TWPA as a source of
two-mode squeezed microwave radiation. We demonstrate broadband entanglement
generation between two modes separated by up to 400 MHz by measuring
logarithmic negativity between 0.27 and 0.51 and collective quadrature
squeezing below the vacuum limit between 1.5 and 2.1 dB. This work opens
interesting perspectives for the exploration of novel microwave photonics
experiments with possible applications in quantum sensing and continuous
variable quantum computing
Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications
This review presents an overview of the thermal properties of mesoscopic
structures. The discussion is based on the concept of electron energy
distribution, and, in particular, on controlling and probing it. The
temperature of an electron gas is determined by this distribution:
refrigeration is equivalent to narrowing it, and thermometry is probing its
convolution with a function characterizing the measuring device. Temperature
exists, strictly speaking, only in quasiequilibrium in which the distribution
follows the Fermi-Dirac form. Interesting nonequilibrium deviations can occur
due to slow relaxation rates of the electrons, e.g., among themselves or with
lattice phonons. Observation and applications of nonequilibrium phenomena are
also discussed. The focus in this paper is at low temperatures, primarily below
4 K, where physical phenomena on mesoscopic scales and hybrid combinations of
various types of materials, e.g., superconductors, normal metals, insulators,
and doped semiconductors, open up a rich variety of device concepts. This
review starts with an introduction to theoretical concepts and experimental
results on thermal properties of mesoscopic structures. Then thermometry and
refrigeration are examined with an emphasis on experiments. An immediate
application of solid-state refrigeration and thermometry is in ultrasensitive
radiation detection, which is discussed in depth. This review concludes with a
summary of pertinent fabrication methods of presented devices.Comment: Close to the version published in RMP; 59 pages, 35 figure
Quantum noise limited microwave amplification using a graphene Josephson junction
Josephson junctions (JJ) and their tunable properties, including their
nonlinearities, form the core of superconducting circuit quantum
electrodynamics (cQED). In quantum circuits, low-noise amplification of feeble
microwave signals is essential and the Josephson parametric amplifiers (JPA)
are the widely used devices. The existing JPAs are based on Al-AlOx-Al tunnel
junctions realized in a superconducting quantum interference device geometry,
where magnetic flux is the knob for tuning the frequency. Recent experimental
realizations of 2D van der Waals JJs provide an opportunity to implement
various cQED devices with the added advantage of tuning the junction properties
and the operating point using a gate potential. While other components of a
possible 2D van der Waals cQED architecture have been demonstrated -- quantum
noise limited amplifier, an essential component, has not been realized. Here we
implement a quantum noise limited JPA, using a graphene JJ, that has linear
resonance gate tunability of 3.5 GHz. We report 24 dB amplification with 10 MHz
bandwidth and -130 dBm saturation power; performance on par with the best
single-junction JPAs. Importantly, our gate tunable JPA works in the
quantum-limited noise regime which makes it an attractive option for highly
sensitive signal processing. Our work has implications for novel bolometers --
the low heat capacity of graphene together with JJ nonlinearity can result in
an extremely sensitive microwave bolometer embedded inside a quantum
noise-limited amplifier. In general, our work will open up exploration of
scalable device architecture of 2D van der Waals materials by integrating a
sensor with the quantum amplifier.Comment: 15 pages, 4 figures, and supplementary informatio
Molecular-Based Optical Measurement Techniques for Transition and Turbulence in High-Speed Flow
High-speed laminar-to-turbulent transition and turbulence affect the control of flight vehicles, the heat transfer rate to a flight vehicle's surface, the material selected to protect such vehicles from high heating loads, the ultimate weight of a flight vehicle due to the presence of thermal protection systems, the efficiency of fuel-air mixing processes in high-speed combustion applications, etc. Gaining a fundamental understanding of the physical mechanisms involved in the transition process will lead to the development of predictive capabilities that can identify transition location and its impact on parameters like surface heating. Currently, there is no general theory that can completely describe the transition-to-turbulence process. However, transition research has led to the identification of the predominant pathways by which this process occurs. For a truly physics-based model of transition to be developed, the individual stages in the paths leading to the onset of fully turbulent flow must be well understood. This requires that each pathway be computationally modeled and experimentally characterized and validated. This may also lead to the discovery of new physical pathways. This document is intended to describe molecular based measurement techniques that have been developed, addressing the needs of the high-speed transition-to-turbulence and high-speed turbulence research fields. In particular, we focus on techniques that have either been used to study high speed transition and turbulence or techniques that show promise for studying these flows. This review is not exhaustive. In addition to the probe-based techniques described in the previous paragraph, several other classes of measurement techniques that are, or could be, used to study high speed transition and turbulence are excluded from this manuscript. For example, surface measurement techniques such as pressure and temperature paint, phosphor thermography, skin friction measurements and photogrammetry (for model attitude and deformation measurement) are excluded to limit the scope of this report. Other physical probes such as heat flux gauges, total temperature probes are also excluded. We further exclude measurement techniques that require particle seeding though particle based methods may still be useful in many high speed flow applications. This manuscript details some of the more widely used molecular-based measurement techniques for studying transition and turbulence: laser-induced fluorescence (LIF), Rayleigh and Raman Scattering and coherent anti-Stokes Raman scattering (CARS). These techniques are emphasized, in part, because of the prior experience of the authors. Additional molecular based techniques are described, albeit in less detail. Where possible, an effort is made to compare the relative advantages and disadvantages of the various measurement techniques, although these comparisons can be subjective views of the authors. Finally, the manuscript concludes by evaluating the different measurement techniques in view of the precision requirements described in this chapter. Additional requirements and considerations are discussed to assist with choosing an optical measurement technique for a given application
Cooling electrons in nanoelectronic devices by on-chip demagnetisation
This thesis describes a novel cooling technique which allows the electrons within nanoelectronic devices to reach new low temperatures: nuclear demagnetisation of copper refrigerant mounted directly onto the chip a device is constructed on. This is within a field which has expanded in interest in recent years, due to the promise of new low electron temperatures allowing the investigation of new physical phenomena, the better fidelity of fundamental quantum effects and the improvement in quantum technologies such as quantum computers and sensors. Throughout the study, the effectiveness of the new technique is verified by applying it to a CBT, a nanoelectronic device which provides primary (accurate without any need for calibration) thermometry of its own internal electron temperature. This thesis follows the development of this technique, starting from the initial proof of concept measurements made using a commercial, cryogen free, dilution refrigerator, as would be found in many low temperature and quantum transport laboratories. Here, the device electrons were cooled from 7 mK, the base temperature of the dilution refrigerator, to 4.5 mK without using any other elaborate experimental constructions, opening the technique up to many other laboratories. This technique was then furthered by applying it to a newly adapted CBT which has the lowest operation temperature capability yet reported of 300 μK. This was done in a dilution refrigerator custom built in Lancaster, resulting in a minimum electron temperature of 1.20 ± 0.03 mK. This has opened the door to a new temperature regime in which to study new quantum effects, and going forward this technique will therefore be applied to other devices in order to enable these further investigations
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