72,270 research outputs found
Hamilton's turns as visual tool-kit for designing of single-qubit unitary gates
Unitary evolutions of a qubit are traditionally represented geometrically as
rotations of the Bloch sphere, but the composition of such evolutions is
handled algebraically through matrix multiplication [of SU(2) or SO(3)
matrices]. Hamilton's construct, called turns, provides for handling the latter
pictorially through the as addition of directed great circle arcs on the unit
sphere S, resulting in a non-Abelian version of the
parallelogram law of vector addition of the Euclidean translation group. This
construct is developed into a visual tool-kit for handling the design of
single-qubit unitary gates. As an application, it is shown, in the concrete
case wherein the qubit is realized as polarization states of light, that all
unitary gates can be realized conveniently through a universal gadget
consisting of just two quarter-wave plates (QWP) and one half-wave plate (HWP).
The analysis and results easily transcribe to other realizations of the qubit:
The case of NMR is obtained by simply substituting and pulses
respectively for QWPs and HWPs, the phases of the pulses playing the role of
the orientation of fast axes of these plates.Comment: 16 Pages, 14 Figures, Published versio
Dynamics of some constrained lattices
We consider the dynamics of lattices which have constrained constitutive
units flexible in only their mutual orientations.
A continuum description is derived through which it is shown that the models
have zero shear velocity, free-particle like internal rotational modes and
volume decreasing linearly with temperature. The relevance of modelsto a range
of problems is pointed out.Comment: 5 pages, 2 EPS figure
A nonlinear-coherence receiver
Mathematical analysis and detailed study of generic model for coherent receiver has demonstrated that nonlinear coherence between given biphase-modulated input signal and supplied reference signal can be used in receivers to improve telecommunication systems
Data-aided carrier tracking loops
Power in composite signal sidebands is used to enhance signal-to-noise ratio in carrier tracking loop, thereby reducing radio loss and decreasing probability of receiver error. By adding quadrature channel to phase-lock-loop detector circuit of receiver, dc component can be fed back into carrier tracking loop
Coherent receiver employing nonlinear coherence detection for carrier tracking
The concept of nonlinear coherence employed in carrier tracking to improve telecommunications efficiency is disclosed. A generic tracking loop for a coherent receiver is shown having seven principle feedback signals which may be selectively added and applied to a voltage controlled oscillator to produce a reference signal that is phase coherent with a received carrier. An eighth feedback signal whose nonrandom components are coherent with the phase detected and filtered carrier may also be added to exploit the sideband power of the received signal. A ninth feedback signal whose nonrandom components are also coherent with the quadrature phase detected and filtered carrier could be additionally or alternatively included in the composite feedback signal to the voltage controlled oscillator
Detection and Implications of a Time-reversal breaking state in underdoped Cuprates
We present general symmetry considerations on how a Time-reversal breaking
state may be detected by angle-resolved photoemission using circularly
polarized photons as has been proposed earlier. Results of recent experiments
utilizing the proposal in underdoped cuprates are analysed and found to be
consistent in their symmetry and magnitude with a theory of the Copper-Oxides.
These togather with evidence for a quantum critical point and marginal
Fermi-liquid properties near optimum doping suggest that a valid microscopic
theory of the phenomena in the cuprates has been found.Comment: A statement on detecting the Anyon state is added and some typos are
subtracte
Status of the ILC Main Linac BPM R&D
An introduction and the status of R&D activities for a high-resolution,
"cold" beam position monitor (BPM) and the related read-out electronics are
discussed. Two different BPM detector concepts, to be attached to the SC
quadrupole and located inside the ILC cryomodule, are currently under
investigation: A resonant dipole-mode cavity-style BPM pickup, developed at
Fermilab, and a re-entrant resonant coaxial waveguide BPM, designed by
CEA-Saclay. While the 1.5 GHz dipole-mode cavity BPM is still in the R&D phase,
the re-entrant BPM has already passed first beam tests, including its read-out
system. Furthermore, the LAPP group is developing radiation tolerant digital
read-out systems, which are tested at the CLIC test facility (CTF).Comment: LCWS / ILC08 conference contribution, 6 pages, 6 figure
Majoranas with and without a 'character': hybridization, braiding and Majorana number
In this paper we demonstrate under what conditions a pseudo-spin degree of
freedom or character can be ascribed to the Majorana bound states (MBS) which
can be created at the end of one dimensional non-interacting systems,
corresponding to D, DIII and BDI in the usual classification scheme. We have
found that such a character is directly related to the class of the topological
superconductor and its description by a , rather than a
, invariant which corresponds to the BDI class. We have also
found that the DIII case with mirror symmetry, which supports multiple MBS, is
in fact equivalent to the BDI class with an additional time-reversal symmetry.
In all cases where a character can be given to the Majorana states we show how
to construct the appropriate operator explicitly in various examples. We also
examine the consequences of the Majorana character by considering possible
hybridization of MBS brought into proximity and find that two MBS with the same
character do not hybridize. Finally, we show that having this character or not
has no consequence on the braiding properties of MBS.Comment: 10 pages, 1 figur
Perceptions and correlates of peer-victimization and bullying
The experiences of peer-victimization and bullying are often treated empirically as though they are conceptually indistinct. Both involve repeated aggression,but definitions of bullying additionally emphasize the importance of aggressor intent and imbalance of power between the aggressor and the victim (Olweus, 1978; Whitney & Smith, 1993). The present study aimed to examine the extent to which peer-victimization and bullying are empirically similar. The sample comprised 1,429 pupils (50.2% male) aged between 8 and 13 years attending mainstream Scottish schools. Self-report questionnaire assessing peer-victimization and bullying, copingstrategy use (WCCL: Hunter, 2000), situational appraisal and depressive symptomatology (Birleson, 1981). Almost one-third (30.7%) of pupils reported experiencing peer-victimization, and of these 38.1% (11.7% of whole sample) were categorized as victims of bullying. Victims of bullying perceived higher levels of threat and lower levels of perceived control. They also reported using more Wishful Thinking and Social Support coping strategies, but did not differ on Problem Focused coping. Bullied pupils also reported higher levels of depressive symptomatology. Peer-victimization and bullying appear to be qualitatively different experiences for children and adolescents, with bullying being the more serious phenomenon
Cellular automata models of traffic flow along a highway containing a junction
We examine various realistic generalizations of the basic cellular automaton
model describing traffic flow along a highway. In particular, we introduce a
{\em slow-to-start} rule which simulates a possible delay before a car pulls
away from being stationary. Having discussed the case of a bare highway, we
then consider the presence of a junction. We study the effects of acceleration,
disorderness, and slow-to-start behavior on the queue length at the entrance to
the highway. Interestingly, the junction's efficiency is {\it improved} by
introducing disorderness along the highway, and by imposing a speed limit.Comment: to appear in J. Phys. A:Math.& General. 15 pages, RevTeX, 3
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