4,455 research outputs found
Addressing student models of energy loss in quantum tunnelling
We report on a multi-year, multi-institution study to investigate student
reasoning about energy in the context of quantum tunnelling. We use ungraded
surveys, graded examination questions, individual clinical interviews, and
multiple-choice exams to build a picture of the types of responses that
students typically give. We find that two descriptions of tunnelling through a
square barrier are particularly common. Students often state that tunnelling
particles lose energy while tunnelling. When sketching wave functions, students
also show a shift in the axis of oscillation, as if the height of the axis of
oscillation indicated the energy of the particle. We find inconsistencies
between students' conceptual, mathematical, and graphical models of quantum
tunnelling. As part of a curriculum in quantum physics, we have developed
instructional materials to help students develop a more robust and less
inconsistent picture of tunnelling, and present data suggesting that we have
succeeded in doing so.Comment: Originally submitted to the European Journal of Physics on 2005 Feb
10. Pages: 14. References: 11. Figures: 9. Tables: 1. Resubmitted May 18 with
revisions that include an appendix with the curriculum materials discussed in
the paper (4 page small group UW-style tutorial
Demonstration of Coherent State Discrimination Using a Displacement Controlled Photon Number Resolving Detector
We experimentally demonstrate a new measurement scheme for the discrimination
of two coherent states. The measurement scheme is based on a displacement
operation followed by a photon number resolving detector, and we show that it
outperforms the standard homodyne detector which we, in addition, proof to be
optimal within all Gaussian operations including conditional dynamics. We also
show that the non-Gaussian detector is superior to the homodyne detector in a
continuous variable quantum key distribution scheme.Comment: 5 pages, 3 figure
Understanding and Affecting Student Reasoning About Sound Waves
Student learning of sound waves can be helped through the creation of
group-learning classroom materials whose development and design rely on
explicit investigations into student understanding. We describe reasoning in
terms of sets of resources, i.e. grouped building blocks of thinking that are
commonly used in many different settings. Students in our university physics
classes often used sets of resources that were different from the ones we wish
them to use. By designing curriculum materials that ask students to think about
the physics from a different view, we bring about improvement in student
understanding of sound waves. Our curriculum modifications are specific to our
own classes, but our description of student learning is more generally useful
for teachers. We describe how students can use multiple sets of resources in
their thinking, and raise questions that should be considered by both
instructors and researchers.Comment: 23 pages, 4 figures, 3 tables, 28 references, 7 notes. Accepted for
publication in the International Journal of Science Educatio
The role of sign in students' modeling of scalar equations
We describe students revising the mathematical form of physics equations to
match the physical situation they are describing, even though their revision
violates physical laws. In an unfamiliar air resistance problem, a majority of
students in a sophomore level mechanics class at some point wrote Newton's
Second Law as F = -ma; they were using this form to ensure that the sign of the
force pointed in a direction consistent with the chosen coordinate system while
assuming that some variables have only positive value. We use one student's
detailed explanation to suggest that students' issues with variables are
context-dependent, and that much of their reasoning is useful for productive
instruction.Comment: 5 pages, 1 figure, to be published in The Physics Teache
Discrimination of Optical Coherent States using a Photon Number Resolving Detector
The discrimination of non-orthogonal quantum states with reduced or without
errors is a fundamental task in quantum measurement theory. In this work, we
investigate a quantum measurement strategy capable of discriminating two
coherent states probabilistically with significantly smaller error
probabilities than can be obtained using non-probabilistic state
discrimination. We find that appropriate postselection of the measurement data
of a photon number resolving detector can be used to discriminate two coherent
states with small error probability. We compare our new receiver to an optimal
intermediate measurement between minimum error discrimination and unambiguous
state discrimination.Comment: 5 pages, 4 figure
Electronic noise-free measurements of squeezed light
We study the implementation of a correlation measurement technique for the
characterization of squeezed light. We show that the sign of the covariance
coefficient revealed from the time resolved correlation data allow us to
distinguish between squeezed, coherent and thermal states. In contrast to the
traditional method of characterizing squeezed light, involving measurement of
the variation of the difference photocurrent, the correlation measurement
method allows to eliminate the contribution of the electronic noise, which
becomes a crucial issue in experiments with dim sources of squeezed light.Comment: submitted for publicatio
Latitudinal variation of the solar photospheric intensity
We have examined images from the Precision Solar Photometric Telescope (PSPT)
at the Mauna Loa Solar Observatory (MLSO) in search of latitudinal variation in
the solar photospheric intensity. Along with the expected brightening of the
solar activity belts, we have found a weak enhancement of the mean continuum
intensity at polar latitudes (continuum intensity enhancement
corresponding to a brightness temperature enhancement of ).
This appears to be thermal in origin and not due to a polar accumulation of
weak magnetic elements, with both the continuum and CaIIK intensity
distributions shifted towards higher values with little change in shape from
their mid-latitude distributions. Since the enhancement is of low spatial
frequency and of very small amplitude it is difficult to separate from
systematic instrumental and processing errors. We provide a thorough discussion
of these and conclude that the measurement captures real solar latitudinal
intensity variations.Comment: 24 pages, 8 figs, accepted in Ap
QPSK coherent state discrimination via a hybrid receiver
We propose and experimentally demonstrate a near-optimal discrimination
scheme for the quadrature phase shift keying protocol (QPSK). We show in theory
that the performance of our hybrid scheme is superior to the standard scheme -
heterodyne detection - for all signal amplitudes and underpin the predictions
with our experimental results. Furthermore, our scheme provides the hitherto
best performance in the domain of highly attenuated signals. The discrimination
is composed of a quadrature measurement, a conditional displacement and a
threshold detector
Using resource graphs to represent conceptual change
We introduce resource graphs, a representation of linked ideas used when
reasoning about specific contexts in physics. Our model is consistent with
previous descriptions of resources and coordination classes. It can represent
mesoscopic scales that are neither knowledge-in-pieces or large-scale concepts.
We use resource graphs to describe several forms of conceptual change:
incremental, cascade, wholesale, and dual construction. For each, we give
evidence from the physics education research literature to show examples of
each form of conceptual change. Where possible, we compare our representation
to models used by other researchers. Building on our representation, we
introduce a new form of conceptual change, differentiation, and suggest several
experimental studies that would help understand the differences between
reform-based curricula.Comment: 27 pages, 14 figures, no tables. Submitted for publication to the
Physical Review Special Topics Physics Education Research on March 8, 200
Probabilistic Cloning of Coherent States without a Phase Reference
We present a probabilistic cloning scheme operating independently of any
phase reference. The scheme is based solely on a phase-randomized displacement
and photon counting, omitting the need for non-classical resources and
non-linear materials. In an experimental implementation, we employ the scheme
to clone coherent states from a phase covariant alphabet and demonstrate that
the cloner is capable of outperforming the hitherto best-performing
deterministic scheme. An analysis of the covariances between the output states
shows that uncorrelated clones can be approached asymptotically. An intriguing
feature is that the trade-off between success rate and achieved fidelity can be
optimized even after the cloning procedure
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