Intrinsic Dissipation in Superconducting Junctions Probed by Qubit Spectroscopy
The study of frequency-dependent intrinsic dissipation in a highly transparent Josephson junction by means of quantum-bit (qubit) spectroscopy is proposed. The spectral density of the effective dissipative bath may contain significant contributions from Andreev bound states coupled to fluctuations of the Josephson phase. Varying either the bias current applied to the junction or magnetic flux through a superconducting ring in the radiofrequency superconducting quantum interference device (rf-SQUID) setup, one can tune the level splitting value close to the bottom of the Josephson potential well. Monitoring the qubit energy relaxation time one can probe the spectral density of the effective dissipative bath and unambiguously identify the contribution emerging from Andreev levels.
We have employed noise thermometry for investigations of thermal relaxation between the electrons and the substrate in nanowires patterned from 40-nm-thick titanium film on top of silicon wafers covered by a native oxide. By controlling the electronic temperature Te by Joule heating at the base temperature of a dilution refrigerator, we probe the electron–phonon coupling and the thermal boundary resistance at temperatures Te = 0.5–3 K. Using a regular T 5-dependent electron–phonon coupling of clean metals and a T 4-dependent interfacial heat flow, we deduce a small contribution for the direct energy transfer from the titanium electrons to the substrate phonons due to inelastic electron-boundary scattering.
The Low Temperature Physics Conference is an international event held every three years, under the auspices of the IUPAP through its Commission C5 on Low Temperature Physics. The aim of these conferences is to exchange information and views among the members of the international scientific community in the general field of Low Temperature Physics. It is a tradition that LT offers updates on the various topics, provided by the highest representatives of the field, as well as oral and poster contributions in the different areas. As usual the conference covers five subtopics:Quantum fluids and solids Superconductivity Cryogenic techniques and applications Magnetism and quantum phase transitions Quantum transport and quantum information in condensed matter
Gothenburg is situated in the center of Scandinavia, on the Swedish West Coast, and is easily accessed by air. The city’s two universities – Chalmers University of Technology and University of Gothenburg – both have a long tradition in low temperature physics research, particularly superconductivity and quantum transport.
Book of abstracts
Majorana zero modes can be simulated in structures based on spin or quasi-spin degrees of freedom, e.g., Josephson-qubit chains. Braiding of Majorana degrees of freedom is realized using T -junctions supplied with an auxiliary spin (ancilla). Motivated by prospective experiments, we analyze the braiding in the spin representation, which provides the basis for the analysis of imperfections characteristic to the spin and qubit designs. The result of the braiding operation is straightforwardly found for the initial basis states of the two qubits and the ancilla, up to phase factors. Here we fix these phase factors and thus describe the complete two-qubit operation. This result is relevant for physical simulation of the Majorana qubits in Josephson-qubit chains and other spin or qubit structures.
A natural atom placed into a cavity with time-dependent parameters can be parametrically excited due to interaction with the quantized photon mode. One of the channels for this process is the dynamical Lamb effect, induced by a nonadiabatic modulation of the atomic-level Lamb shift. However, in experiments with natural atoms it is quite difficult to isolate this effect from other mechanisms of atom excitation. We point out that a transmission line cavity coupled with a superconducting qubit (an artificial macroscopic atom) provides a unique platform for observation of the dynamical Lamb effect. A key idea is to exploit a dynamically tunable qubit-resonator coupling, which was implemented quite recently. By varying the coupling nonadiabatically, it is possible to parametrically excite a qubit through a nonadiabatic modulation of the Lamb shift, even if the cavity was initially empty. The dynamics of such a coupled system is studied within the Rabi model with a time-dependent coupling constant and beyond the rotating-wave approximation. An efficient method to increase the effect through the periodic and nonadiabatic switching of the qubit-resonator coupling energy is proposed. © 2015 American Physical Society. ©2015 American Physical Society.
Superconducting properties of metallic nanowires can be entirely different from those of bulk superconductors because of the dominating role played by thermal and quantum fluctuations of the order parameter. For superconducting channels with diameters below ∼ 50 nm fluctuations of the phase of the complex order parameter - the phase slippage - lead to non-zero resistance below the critical temperature. Fluctuations of the modulus of the complex order parameter broaden the gap edge of the quasiparticle energy spectrum and modify the density of states. In extreme case of very narrow channels imbedded in high-impedance environment (which fix the charge and, hence, enable strong fluctuations of the quantum-conjugated variable, the phase) the superconductor can be driven to insulating state – the Coulomb blockade. We review recent experimental activities in the field demonstrating rather unusual phenomena.
The materials of The International Scientific – Practical Conference is presented below.
The Conference reflects the modern state of innovation in education, science, industry and social-economic sphere, from the standpoint of introducing new information technologies.
It is interesting for a wide range of researchers, teachers, graduate students and professionals in the field of innovation and information technologies.
Molecular dynamics simulations are carried out to study the translational and rotational diffusion of a single Janus particle immersed in a dense Lennard-Jones fluid. We consider a spherical particle with two hemispheres of different wettabilities. The analysis of the particle dynamics is based on the time-dependent orientation tensor, particle displacement, as well as the translational and angular velocity autocorrelation functions. It was found that both translational and rotational diffusion coefficients increase with decreasing surface energy at the nonwetting hemisphere, provided that the wettability of the other hemisphere remains unchanged. We also observed that in contrast to homogeneous particles, the nonwetting hemisphere of the Janus particle tends to rotate in the direction of the displacement vector during the rotational relaxation time.
International Conference on Micro- and Nano-Electronics 2016
Molecular dynamics simulations are carried out to study the translational and rotational diffusion of
a single Janus particle immersed in a dense Lennard-Jones fluid. We consider a spherical particle
with two hemispheres of different wettabilities. The analysis of the particle dynamics is based
on the time-dependent orientation tensor, particle displacement, as well as the translational and
angular velocity autocorrelation functions. It was found that both translational and rotational diffusion
coefficients increase with decreasing surface energy at the nonwetting hemisphere, provided that
the wettability of the other hemisphere remains unchanged. We also observed that in contrast to
homogeneous particles, the nonwetting hemisphere of the Janus particle tends to rotate in the
direction of the displacement vector during the rotational relaxation time.
The influence of the external pressure and surface energy on the wetting transition at nanotextured interfaces is studied using molecular dynamics and continuum simulations. The surface roughness of the composite interface is introduced via an array of spherical nanoparticles with controlled wettability. We find that in the absence of an external pressure, the liquid interface is flat and its location relative to the solid substrate is determined by the particle size and the local contact angle. With increasing pressure on the liquid film, the interface becomes more curved and the three-phase contact line is displaced along the spherical surface but remains stable due to re-entrant geometry. It is demonstrated that the results of molecular dynamics simulations for the critical pressure of the Cassie-Baxter wetting state agree well with the estimate of the critical pressure obtained by numerical minimization of the interfacial energy.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.