1,016 research outputs found
Quantum Tunneling Detection of Two-photon and Two-electron Processes
We analyze the operation of a quantum tunneling detector coupled to a
coherent conductor. We demonstrate that in a certain energy range the output of
the detector is determined by two-photon processes, two-electron processes and
the interference of the two. We show how the individual contributions of these
processes can be resolved in experiments.Comment: 4 pages, 4 figure
Tunneling into Multiwalled Carbon Nanotubes: Coulomb Blockade and Fano Resonance
Tunneling spectroscopy measurements of single tunnel junctions formed between
multiwalled carbon nanotubes (MWNTs) and a normal metal are reported. Intrinsic
Coulomb interactions in the MWNTs give rise to a strong zero-bias suppression
of a tunneling density of states (TDOS) that can be fitted numerically to the
environmental quantum-fluctuation (EQF) theory. An asymmetric conductance
anomaly near zero bias is found at low temperatures and interpreted as Fano
resonance in the strong tunneling regime.Comment: 4 pages, 4 figure
Loss of quantum coherence due to non-stationary glass fluctuations
Low-temperature dynamics of insulating glasses is dominated by a macroscopic
concentration of tunneling two-level systems (TTLS). The distribution of the
switching/relaxation rates of TTLS is exponentially broad, which results in
non-equilibrium state of the glass at arbitrarily long time-scales. Due to the
electric dipolar nature, the switching TTLS generate fluctuating
electromagnetic fields. We study the effect of the non-thermal slow fluctuators
on the dephasing of a solid state qubit. We find that at low enough
temperatures, non-stationary contribution can dominate the stationary (thermal)
one, and discuss how this effect can be minimized.Comment: 4 page
Inverse proximity effect in superconductors near ferromagnetic material
We study the electronic density of states in a mesoscopic superconductor near
a transparent interface with a ferromagnetic metal. In our tunnel spectroscopy
experiment, a substantial density of states is observed at sub-gap energies
close to a ferromagnet. We compare our data with detailed calculations based on
the Usadel equation, where the effect of the ferromagnet is treated as an
effective boundary condition. We achieve an excellent agreement with theory
when non-ideal quality of the interface is taken into account.Comment: revised, 7 pages, 3 figure
Dynamical conductance in the two-channel Kondo regime of a double dot system
We study finite-frequency transport properties of the double-dot system
recently constructed to observe the two-channel Kondo effect [R. M. Potok et
al., Nature 446, 167 (2007)]. We derive an analytical expression for the
frequency-dependent linear conductance of this device in the Kondo regime. We
show how the features characteristic of the 2-channel Kondo quantum critical
point emerge in this quantity, which we compute using the results of conformal
field theory as well as numerical renormalization group methods. We determine
the universal cross-over functions describing non-Fermi liquid vs. Fermi liquid
cross-overs and also investigate the effects of a finite magnetic field.Comment: 11 pages in PRB forma
Nonequilibrium plasmons and transport properties of a double--junction quantum wire
We study theoretically the current-voltage characteristics, shot noise, and
full counting statistics of a quantum wire double barrier structure. We model
each wire segment by a spinless Luttinger liquid. Within the sequential
tunneling approach, we describe the system's dynamics using a master equation.
We show that at finite bias the non-equilibrium distribution of plasmons in the
central wire segment leads to increased average current, enhanced shot noise,
and full counting statistics corresponding to a super-Poissonian process. These
effects are particularly pronounced in the strong interaction regime, while in
the non-interacting case we recover results obtained earlier using detailed
balance arguments.Comment: 22 pages, RevTex 2-column, 11 figure
The Influence of Electro-Mechanical Effects on Resonant Electron Tunneling Through Small Carbon Nano-Peapods
The influence of a fullerene molecule trapped inside a single-wall carbon
nanotube on resonant electron transport at low temperatures and strong
polaronic coupling is theoretically discussed. Strong peak to peak fluctuations
and anomalous temperature behavior of conductance amplitudes are predicted and
investigated. The influence of the chiral properties of carbon nanotubes on
transport is also studied.Comment: 17 pages, 3 figures. Replaced with published version. Important
changes. Open access: http://stacks.iop.org/1367-2630/10/04304
Quantum charge diffusion in underdamped Josephson junctions and superconducting nanowires
The effect of quantum fluctuations on the current-voltage characteristics of
Josephson junctions and superconducting nanowires is studied in the underdamped
limit. Quantum fluctuations induce transitions between a Coulomb--blockade and
a supercurrent branch, and can significantly modify the shape of
current-voltage characteristics in the case of a highly resistive environment.
Owing to the phase-charge duality, our results can be directly extended to the
opposite overdamped limit.Comment: 6 pages, 2 figures, replaced with published versio
Learning on the move: exploring work with vulnerable young men through the lens of movement
This paper discusses a practice context in which process and movement are central to the provision of care and support. It draws on data from a research project conducted with The Men’s Room, Manchester, England which used ethnographic and mobile methods to explore the complex task staff undertake in engaging and supporting highly vulnerable young men. The organisation’s commitment to getting alongside these young men includes a mobile and highly improvised use of temporary city centre spaces for delivering its work. In this paper, I argue that these movements of practice are not simply a logistical necessity or a physical activity, but involve a kinetic way of attending, reflecting, thinking and knowing in which the organisation’s movements are intrinsic to the provision of care and support
Quantum nondemolition-like, fast measurement scheme for a superconducting qubit
We present a measurement protocol for a flux qubit coupled to a
dc-Superconducting QUantum Interference Device (SQUID), representative of any
two-state system with a controllable coupling to an harmonic oscillator
quadrature, which consists of two steps. First, the qubit state is imprinted
onto the SQUID via a very short and strong interaction. We show that at the end
of this step the qubit dephases completely, although the perturbation of the
measured qubit observable during this step is weak. In the second step,
information about the qubit is extracted by measuring the SQUID. This step can
have arbitrarily long duration, since it no longer induces qubit errors.Comment: published version, minor correction
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