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

Single fermion manipulation via superconducting phase differences in multiterminal Josephson junctions

We show how the superconducting phase difference in a Josephson junction may be used to split the Kramers degeneracy of its energy levels and to remove all the properties associated with time reversal symmetry. The superconducting phase difference is known to be ineffective in two-terminal short Josephson junctions, where irrespective of the junction structure the induced Kramers degeneracy splitting is suppressed and the ground state fermion parity must stay even, so that a protected zero-energy Andreev level crossing may never appear. Our main result is that these limitations can be completely avoided by using multi-terminal Josephson junctions. There the Kramers degeneracy breaking becomes comparable to the superconducting gap, and applying phase differences may cause the change of the ground state fermion parity from even to odd. We prove that the necessary condition for the appearance of a fermion parity switch is the presence of a "discrete vortex" in the junction: the situation when the phases of the superconducting leads wind by $2\pi$. Our approach offers new strategies for creation of Majorana bound states as well as spin manipulation. Our proposal can be implemented using any low density, high spin-orbit material such as InAs quantum wells, and can be detected using standard tools.Comment: Source code available as ancillary files. 10 pages, 7 figures. v2: minor changes, published versio

Exploration and categorization of pre-service physics teachers' alternative conceptions in superconductivity and nanotechnology

An exploratory case study research design was followed to explore and categorize 23 pre-service physics teachers’ understanding in the fields of superconductivity and nanotechnology at the Sultan Qaboos University in Oman. To elicit their responses, a five-stage categorical framework analysis was used. The five stages included identification of the thematic framework, familiarization, coding, placing the categories on a chart and finally, interpretation. A conceptual survey test (Conceptual Survey of Superconductivity and Nanotechnology) was administered to the pre-service physics teachers to form four independently homogenous ability focus groups. This was followed by focus group discussions whose data were analyzed to group their conceptions in both the epistemological as well as ontological categories. From the focus group discussions, six categories were considered from previous studies, namely; lateral alternative conceptions, ontological conceptions, naïve physics, Ohm’s p-primes, mixed conceptions and loose ideas. Since this was a pre-instructional study, naïve physics ideas and lateral alternative conceptions were dominant. Naïve physics refers to the untrained student or human perception of various physical phenomena while lateral alternative conception refers the misconceptions individuals have on ideas that may be inconsistent with scientifically acceptable facts. Findings indicate that the pre-service teachers’ conceptions deviated from canonical scientific concepts, are diversified and inconsistent. The knowledge on pre-instructional conceptions will influence the development of evidence-based pedagogy, which is fundamental to the development of an effective physics education curriculum.Institute for Science and Technology Education (ISTE)M. Sc. (Physics Education

Superconducting detectors for rare event searches in experimental astroparticle physics

Superconducting detectors have become an important tool in experimental astroparticle physics, which seeks to provide a fundamental understanding of the Universe. In particular, such detectors have demonstrated excellent potential in two challenging research areas involving rare event search experiments, namely, the direct detection of dark matter and the search for neutrinoless double beta decay. Here, we review the superconducting detectors that have been and are planned to be used in these two categories of experiments. We first provide brief histories of the two research areas and outline their significance and challenges in astroparticle physics. Then, we present an extensive overview of various types of superconducting detectors with a focus on sensor technologies and detector physics, which are based on calorimetric measurements and heat flow in the detector components. Finally, we introduce leading experiments and discuss their future prospects for the detection of dark matter and the search for neutrinoless double beta decay employing superconducting detectors

Intrinsic decoherence in superconducting quantum circuits

Decoherence and parameter fluctuations are two of the mayor obstacles for solid-state quantum computing. In this work, decoherence in superconducting qubits of the transmon type is investigated. For this purpose, a time-multiplexed measurement protocol was developed and applied in long-term measurements. The resulting simultaneous measurement of the qubit\u27s relaxation and dephasing rate, as well as its resonance frequency enables analysis of correlations between these parameters. A spectral noise analysis complements these measurements. Together, the results agree well with the interacting defect model of two-level-systems and yield information about the microscopic origin of the intrinsic decoherence mechanisms in Josephson qubits. Our measurements show inherent correlations between dephasing and fluctuations in qubit frequency on the timescale of seconds to days, which is attributed to the influence of individual defects, located close to conductor edges. Cross-correlation and spectral noise analysis confirm this interpretation and ascribe the source of fluctuation to interactions between thermal fluctuators and surface defects. Single defects reducing the coherence of qubits by up to one order of magnitude are a major challenge for future quantum computers. Non-tunable qubits are intrinsically insensitive to some decoherence channels and thus ideal for this fundamental analysis. However, to widen the focus and contrast the results of different material systems, we pursue the fabrication of voltage controlled gatemon qubits. In the course of this work, the theoretical foundation and technical implementation of transmon qubits based on regular Josephson weak links, and semiconducting nanowires is given. The experimental design and measurement setup are explained in detail. Our findings make continuous re-calibration a necessity in today\u27s solid-state qubits, although new materials or processing techniques might mitigate the problem. However, the results of this work imply that fundamental improvements of qubit parameter stability are necessary in order to realize scalable and coherent qubit circuits