837 research outputs found
A tunable coupling scheme for implementing high-fidelity two-qubit gates
The prospect of computational hardware with quantum advantage relies
critically on the quality of quantum gate operations. Imperfect two-qubit gates
is a major bottleneck for achieving scalable quantum information processors.
Here, we propose a generalizable and extensible scheme for a two-qubit coupler
switch that controls the qubit-qubit coupling by modulating the coupler
frequency. Two-qubit gate operations can be implemented by operating the
coupler in the dispersive regime, which is non-invasive to the qubit states. We
investigate the performance of the scheme by simulating a universal two-qubit
gate on a superconducting quantum circuit, and find that errors from known
parasitic effects are strongly suppressed. The scheme is compatible with
existing high-coherence hardware, thereby promising a higher gate fidelity with
current technologies
Dynamic modelling of nitrous oxide emissions from three Swedish sludge liquor treatment systems
The objective of this paper is to model the dynamics and validate the results of nitrous oxide (N2O) emissions from three Swedish nitrifying/denitrifying, nitritation and anammox systems treating real anaerobic digester sludge liquor. The Activated Sludge Model No. 1 is extended to describe N2O production by both heterotrophic and autotrophic denitrification. In addition, mass transfer equations are implemented to characterize the dynamics of N2O in the water and the gas phases. The biochemical model is simulated and validated for two hydraulic patterns: (1) a sequencing batch reactor; and (2) a moving-bed biofilm reactor. Results show that the calibrated model is partly capable of reproducing the behaviour of N2O as well as the nitritation/nitrification/denitrification dynamics. However, the results emphasize that additional work is required before N2O emissions from sludge liquor treatment plants can be generally predicted with high certainty by simulations. Continued efforts should focus on determining the switching conditions for different N2O formation pathways and, if full-scale data are used, more detailed modelling of the measurement devices might improve the conclusions that can be drawn.</jats:p
Didactical use of a remote lab: a qualitative reflection of a teacher
This work describes the teacher reflections about a didactical
implementation using a remote laboratory and their impact on his
practice. These reflections are analyzed from three different
perspectives: how the literature review influenced the design of
the didactical implementation (namely the first); how his
reflection upon his practice influenced its modifications; how his
research activity impacted and affected his teaching practices in
the subsequent implementations and guided the modifications
made. The remote lab was introduced in a Physics Course in an
Engineering degree and was intended to be a learning space where
students had the opportunity to practice before the lab class,
supporting the development of experimental competences,
fundamental in an engineer profile. After the first implementation
in 2016/17 academic year it has undergone two subsequent
editions with adjustments and modifications.
Some features previously reported in literature such as: teacher’s
experience with VISIR, the importance of an introductory activity
and defining VISIR tasks objectives, were corroborated by the
teacher during his practice and research. Others, such as the
difficulty some students have in understanding the difference
between simulation and remote labs appeared directly from his
practice and were pursued in his research in order to deeply
understand its implications
Supersymmetry Breaking in Chern-Simons-matter Theories
Some of supersymmetric Chern-Simons theories are known to exhibit
supersymmetry breaking when the Chern-Simons level is less than a certain
number. The mechanism of the supersymmetry breaking is, however, not clear from
the field theory viewpoint. In this paper, we discuss vacuum states of pure Chern-Simons theory and Chern-Simons-matter theories of
quiver type using related theories in which Chern-Simons terms are replaced
with (anti-)fundamental chiral multiplets. In the latter theories,
supersymmetry breaking can be shown to occur by examining that the vacuum
energy is non-zero.Comment: 17 pages, 3 figures, v2) references adde
Background field formalism and construction of effective action for N=2, d=3 supersymmetric gauge theories
We review the background field method for three-dimensional Yang-Mills and
Chern-Simons models in N=2 superspace. Superfield proper time (heat kernel)
techniques are developed and exact expressions of heat kernels for constant
backgrounds are presented. The background field method and heat kernel
techniques are applied for evaluating the low-energy effective actions in N=2
supersymmetric Yang-Mills and Chern-Simons models as well as in N=4 and N=8 SYM
theories.Comment: 1+30 pages, dedicated to the 60 year Jubilee of Professor D.I.
Kazakov; references added. arXiv admin note: substantial text overlap with
arXiv:1010.496
Notes on Supersymmetry Enhancement of ABJM Theory
We study the supersymmetry enhancement of ABJM theory. Starting from a supersymmetric Chern-Simons matter theory with gauge group
U(2)U(2) which is a truncated version of the ABJM theory, we find by
using the monopole operator that there is additional supersymmetry
related to the gauge group. We show this additional supersymmetry can combine
with supersymmetry of the original ABJM theory to an enhanced
SUSY with gauge group U(2)U(2) in the case . We
also discuss the supersymmetry enhancement of the ABJM theory with
U()U() gauge group and find a condition which should be satisfied
by the monopole operator.Comment: 23 pages, no figure, minor corrections, version to appear in JHE
Effective action of three-dimensional extended supersymmetric matter on gauge superfield background
We study the low-energy effective actions for gauge superfields induced by
quantum N=2 and N=4 supersymmetric matter fields in three-dimensional Minkowski
space. Analyzing the superconformal invariants in the N=2 superspace we propose
a general form of the N=2 gauge invariant and superconformal effective action.
The leading terms in this action are fixed by the symmetry up to the
coefficients while the higher order terms with respect to the Maxwell field
strength are found up to one arbitrary function of quasi-primary N=2
superfields constructed from the superfield strength and its covariant spinor
derivatives. Then we find this function and the coefficients by direct quantum
computations in the N=2 superspace. The effective action of N=4 gauge multiplet
is obtained by generalizing the N=2 effective action.Comment: 1+27 pages; v2: minor corrections, references adde
Measurement of finite-frequency current statistics in a single-electron transistor
Electron transport in nano-scale structures is strongly influenced by the
Coulomb interaction which gives rise to correlations in the stream of charges
and leaves clear fingerprints in the fluctuations of the electrical current. A
complete understanding of the underlying physical processes requires
measurements of the electrical fluctuations on all time and frequency scales,
but experiments have so far been restricted to fixed frequency ranges as
broadband detection of current fluctuations is an inherently difficult
experimental procedure. Here we demonstrate that the electrical fluctuations in
a single electron transistor (SET) can be accurately measured on all relevant
frequencies using a nearby quantum point contact for on-chip real-time
detection of the current pulses in the SET. We have directly measured the
frequency-dependent current statistics and hereby fully characterized the
fundamental tunneling processes in the SET. Our experiment paves the way for
future investigations of interaction and coherence induced correlation effects
in quantum transport.Comment: 7 pages, 3 figures, published in Nature Communications (open access
Calculation of parity and time invariance violation in the radium atom
Parity (P) and time (T) invariance violating effects in the Ra atom are
strongly enhanced due to close states of opposite parity, the large nuclear
charge Z and the collective nature of P,T-odd nuclear moments. We have
performed calculations of the atomic electric dipole moments (EDM) produced by
the electron EDM and the nuclear magnetic quadrupole and Schiff moments. We
have also calculated the effects of parity non-conservation produced by the
nuclear anapole moment and the weak charge. Our results show that as a rule the
values of these effects are much larger than those considered so far in other
atoms (enhancement is up to 10^5 times).Comment: 18 pages; LaTeX; Submitted to Phys. Rev.
Superconformal M2-branes and generalized Jordan triple systems
Three-dimensional conformal theories with six supersymmetries and SU(4)
R-symmetry describing stacks of M2-branes are here proposed to be related to
generalized Jordan triple systems. Writing the four-index structure constants
in an appropriate form, the Chern-Simons part of the action immediately
suggests a connection to such triple systems. In contrast to the previously
considered three-algebras, the additional structure of a generalized Jordan
triple system is associated to a graded Lie algebra, which corresponds to an
extension of the gauge group. In this note we show that the whole theory with
six manifest supersymmetries can be naturally expressed in terms of such a
graded Lie algebra. Also the BLG theory with eight supersymmetries is included
as a special case.Comment: 15 pages, v2 and v3: minor corrections and clarifications, references
added, v2: section 4 extended, v3: published versio
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