74 research outputs found
Questions of Transfer: Writers\u27 Perspective on Familiar/Unfamiliar Writing tasks in a Capstone Writing Course
Understanding what students bring from one writing context to another may the central concern for teachers of writing from elementary school to adult learning. Research from the field of composition studies offers knowledge about writing as process(es) (Emig, 1971; Shaughnessy, 1979; Russell, 1999), as socially constructed performances (Flower & Hayes, 1980; Bartholomae, 1985; Bloom, 1985), and as part of a larger activity system (Russell, 1997). This dissertation ties together theories of writing as an activity in a broader system of tools and outcomes and current research on transfer in writing in order to illustrate writers\u27 perspectives on particular writing tasks. Essential to the understanding of what students are doing is to know what tools students report using to complete familiar and unfamiliar writing tasks. Data collected include surveys of 148 students in a capstone writing course as well as interviews from 13 students who completed the survey while enrolled in the capstone writing course. Findings suggest that the concept of high-road transfer (Perkins & Salomon, 1988) is not present in participants\u27 writing skills, processes, and knowledges as they approach what they perceive as unfamiliar writing tasks. Significant to this study is the finding that participants\u27 perception informed their description of writing tasks. Certain familiar writing tasks were described as unfamiliar if parts of the tasks were altered. Furthermore, the perception of a writing task as unfamiliar informed the participant\u27s use of external tools. Some participants experienced what the researcher termed a moment of erasure in which they claimed that the unfamiliar writing task was completely new and they had no idea what to do. The pedagogical implications are that if participants do not perceive certain familiar writing skills as applicable to the current task—when in fact, they should be, then it is as if those skills do not exist. Teaching for the unfamiliar may help to avoid the moment of erasure. The final chapter presents pedagogical implications for instructors in light of the findings regarding writers\u27 perspectives on familiar and unfamiliar writing tasks
Combination of a magnetic Feshbach resonance and an optical bound-to-bound transition
We use laser light near resonant with an optical bound-to-bound transition to
shift the magnetic field at which a Feshbach resonance occurs. We operate in a
regime of large detuning and large laser intensity. This reduces the
light-induced atom-loss rate by one order of magnitude compared to our previous
experiments [D.M. Bauer et al. Nature Phys. 5, 339 (2009)]. The experiments are
performed in an optical lattice and include high-resolution spectroscopy of
excited molecular states, reported here. In addition, we give a detailed
account of a theoretical model that describes our experimental data
Atom-molecule Rabi oscillations in a Mott insulator
We observe large-amplitude Rabi oscillations between an atomic and a
molecular state near a Feshbach resonance. The experiment uses 87Rb in an
optical lattice and a Feshbach resonance near 414 G. The frequency and
amplitude of the oscillations depend on magnetic field in a way that is well
described by a two-level model. The observed density dependence of the
oscillation frequency agrees with the theoretical expectation. We confirmed
that the state produced after a half-cycle contains exactly one molecule at
each lattice site. In addition, we show that for energies in a gap of the
lattice band structure, the molecules cannot dissociate
Remote Entanglement between a Single Atom and a Bose-Einstein Condensate
Entanglement between stationary systems at remote locations is a key resource
for quantum networks. We report on the experimental generation of remote
entanglement between a single atom inside an optical cavity and a Bose-Einstein
condensate (BEC). To produce this, a single photon is created in the
atom-cavity system, thereby generating atom-photon entanglement. The photon is
transported to the BEC and converted into a collective excitation in the BEC,
thus establishing matter-matter entanglement. After a variable delay, this
entanglement is converted into photon-photon entanglement. The matter-matter
entanglement lifetime of 100 s exceeds the photon duration by two orders
of magnitude. The total fidelity of all concatenated operations is 95%. This
hybrid system opens up promising perspectives in the field of quantum
information
New Aspects of Geometric Phases in Experiments with polarized Neutrons
Geometric phase phenomena in single neutrons have been observed in
polarimeter and interferometer experiments. Interacting with static and time
dependent magnetic fields, the state vectors acquire a geometric phase tied to
the evolution within spin subspace. In a polarimeter experiment the
non-additivity of quantum phases for mixed spin input states is observed. In a
Si perfect-crystal interferometer experiment appearance of geometric phases,
induced by interaction with an oscillating magnetic field, is verified. The
total system is characterized by an entangled state, consisting of neutron and
radiation fields, governed by a Jaynes-Cummings Hamiltonian. In addition, the
influence of the geometric phase on a Bell measurement, expressed by the
Clauser-Horne-Shimony-Holt (CHSH) inequality, is studied. It is demonstrated
that the effect of geometric phase can be balanced by an appropriate change of
Bell angles.Comment: 17 pages, 9 figure
Lieb-Liniger model of a dissipation-induced Tonks-Girardeau gas
We show that strong inelastic interactions between bosons in one dimension
create a Tonks-Girardeau gas, much as in the case of elastic interactions. We
derive a Markovian master equation that describes the loss caused by the
inelastic collisions. This yields a loss rate equation and a dissipative
Lieb-Liniger model for short times. We obtain an analytic expression for the
pair correlation function in the limit of strong dissipation. Numerical
calculations show how a diverging dissipation strength leads to a vanishing of
the actual loss rate and renders an additional elastic part of the interaction
irrelevant
Controlling a magnetic Feshbach resonance with laser light
The capability to tune the strength of the elastic interparticle interaction
is crucial for many experiments with ultracold gases. Magnetic Feshbach
resonances are a tool widely used for this purpose, but future experiments
would benefit from additional flexibility such as spatial modulation of the
interaction strength on short length scales. Optical Feshbach resonances offer
this possibility in principle, but suffer from fast particle loss due to
light-induced inelastic collisions. Here we show that light near-resonant with
a molecular bound-to-bound transition can be used to shift the magnetic field
at which a magnetic Feshbach resonance occurs. This makes it possible to tune
the interaction strength with laser light and at the same time induce
considerably less loss than an optical Feshbach resonance would do
Electrically-Pumped Wavelength-Tunable GaAs Quantum Dots Interfaced with Rubidium Atoms
We demonstrate the first wavelength-tunable electrically-pumped source of
non-classical light that can emit photons with wavelength in resonance with the
D2 transitions of 87Rb atoms. The device is fabricated by integrating a novel
GaAs single-quantum-dot light-emitting-diode (LED) onto a piezoelectric
actuator. By feeding the emitted photons into a 75-mm-long cell containing warm
87Rb atom vapor, we observe slow-light with a temporal delay of up to 3.4 ns.
In view of the possibility of using 87Rb atomic vapors as quantum memories,
this work makes an important step towards the realization of hybrid-quantum
systems for future quantum networks
Strong dissipation inhibits losses and induces correlations in cold molecular gases
Atomic quantum gases in the strong-correlation regime offer unique
possibilities to explore a variety of many-body quantum phenomena. Reaching
this regime has usually required both strong elastic and weak inelastic
interactions, as the latter produce losses. We show that strong inelastic
collisions can actually inhibit particle losses and drive a system into a
strongly-correlated regime. Studying the dynamics of ultracold molecules in an
optical lattice confined to one dimension, we show that the particle loss rate
is reduced by a factor of 10. Adding a lattice along the one dimension
increases the reduction to a factor of 2000. Our results open up the
possibility to observe exotic quantum many-body phenomena with systems that
suffer from strong inelastic collisions
- …