72 research outputs found
Evolution of circular, non-equatorial orbits of Kerr black holes due to gravitational-wave emission: II. Inspiral trajectories and gravitational waveforms
The inspiral of a ``small'' () compact body into a
``large'' () black hole is a key source of
gravitational radiation for the space-based gravitational-wave observatory
LISA. The waves from such inspirals will probe the extreme strong-field nature
of the Kerr metric. In this paper, I investigate the properties of a restricted
family of such inspirals (the inspiral of circular, inclined orbits) with an
eye toward understanding observable properties of the gravitational waves that
they generate. Using results previously presented to calculate the effects of
radiation reaction, I assemble the inspiral trajectories (assuming that
radiation reacts adiabatically, so that over short timescales the trajectory is
approximately geodesic) and calculate the wave generated as the compact body
spirals in. I do this analysis for several black hole spins, sampling a range
that should be indicative of what spins we will encounter in nature. The spin
has a very strong impact on the waveform. In particular, when the hole rotates
very rapidly, tidal coupling between the inspiraling body and the event horizon
has a very strong influence on the inspiral time scale, which in turn has a big
impact on the gravitational wave phasing. The gravitational waves themselves
are very usefully described as ``multi-voice chirps'': the wave is a sum of
``voices'', each corresponding to a different harmonic of the fundamental
orbital frequencies. Each voice has a rather simple phase evolution. Searching
for extreme mass ratio inspirals voice-by-voice may be more effective than
searching for the summed waveform all at once.Comment: 15 pages, 11 figures, accepted for publication in PRD. This version
incorporates referee's comments, and is much less verbos
Control of an atom laser using feedback
A generalised method of using feedback to control Bose-Einstein condensates
is introduced. The condensates are modelled by the Gross-Pitaevskii equation,
so only semiclassical fluctations can be suppressed, and back-action from the
measurement is ignored. We show that for any available control, a feedback
scheme can be found to reduce the energy while the appropriate moment is still
dynamic. We demonstrate these schemes by considering a condensate trapped in a
harmonic potential that can be modulated in strength and position. The
formalism of our feedback scheme also allows the inclusion of certain types of
non-linear controls. If the non-linear interaction between the atoms can be
controlled via a Feshbach resonance, we show that the feedback process can
operate with a much higher efficiency.Comment: 6 pages, 7 figure
Mode Selectivity and Stability of Continuously Pumped Atom Lasers
A semiclassical, multimode model of a continuously pumped atom laser is presented. For a spatially independent coupling process it is found that the system is unstable below a critical scattering length. As large atomic interactions will increase the phase diffusion of the lasing mode, it is desirable to obtain a stable atom laser with low nonlinearity. It is shown that spatially dependent pumping stabilizes the atom laser to a finite number of modes, and can induce single-mode operation
Quantum Kinetic Theory III: Quantum kinetic master equation for strongly condensed trapped systems
We extend quantum kinetic theory to deal with a strongly Bose-condensed
atomic vapor in a trap. The method assumes that the majority of the vapor is
not condensed, and acts as a bath of heat and atoms for the condensate. The
condensate is described by the particle number conserving Bogoliubov method
developed by one of the authors. We derive equations which describe the
fluctuations of particle number and phase, and the growth of the Bose-Einstein
condensate. The equilibrium state of the condensate is a mixture of states with
different numbers of particles and quasiparticles. It is not a quantum
superposition of states with different numbers of particles---nevertheless, the
stationary state exhibits the property of off-diagonal long range order, to the
extent that this concept makes sense in a tightly trapped condensate.Comment: 3 figures submitted to Physical Review
Entanglement of solid-state qubits by measurement
We show that two identical solid-state qubits can be made fully entangled
(starting from completely mixed state) with probability 1/4 just measuring them
by a detector, equally coupled to the qubits. This happens in the case of
repeated strong (projective) measurements as well as in a more realistic case
of weak continuous measurement. In the latter case the entangled state can be
identified by a flat spectrum of the detector shot noise, while the
non-entangled state (probability 3/4) leads to a spectral peak at the Rabi
frequency with the maximum peak-to-pedestal ratio of 32/3.Comment: 5 pages, 2 figure
Stationary quantum statistics of a non-Markovian atom laser
We present a steady state analysis of a quantum-mechanical model of an atom
laser. A single-mode atomic trap coupled to a continuum of external modes is
driven by a saturable pumping mechanism. In the dilute flux regime, where
atom-atom interactions are negligible in the output, we have been able to solve
this model without making the Born-Markov approximation. The more exact
treatment has a different effective damping rate and occupation of the lasing
mode, as well as a shifted frequency and linewidth of the output. We examine
gravitational damping numerically, finding linewidths and frequency shifts for
a range of pumping rates. We treat mean field damping analytically, finding a
memory function for the Thomas-Fermi regime. The occupation and linewidth are
found to have a nonlinear scaling behavior which has implications for the
stability of atom lasers.Comment: 12 pages, 2 figures, submitted to PR
Selective quantum evolution of a qubit state due to continuous measurement
We consider a two-level quantum system (qubit) which is continuously measured
by a detector. The information provided by the detector is taken into account
to describe the evolution during a particular realization of measurement
process. We discuss the Bayesian formalism for such ``selective'' evolution of
an individual qubit and apply it to several solid-state setups. In particular,
we show how to suppress the qubit decoherence using continuous measurement and
the feedback loop.Comment: 15 pages (including 9 figures
Radioimmunotherapy of B-cell lymphoma with radiolabelled anti-CD20 monoclonal antibodies
CD20 has proven to be an excellent target for the treatment of B-cell lymphoma, first for the chimeric monoclonal antibody rituximab (Rituxan™), and more recently for the radiolabelled antibodies Y-90 ibritumomab tiuxetan (Zevalin™) and I-131 tositumomab (Bexxar™). Radiation therapy effects are due to beta emissions with path lengths of 1–5 mm; gamma radiation emitted by I-131 is the only radiation safety issue for either product. Dose-limiting toxicity for both radiolabelled antibodies is reversible bone marrow suppression. They produce response rates of 70%–90% in low-grade and follicular lymphoma and 40%–50% in transformed low-grade or intermediate-grade lymphomas. Both products produce higher response rates than related unlabelled antibodies, and both are highly active in patients who are relatively resistant to rituximab-based therapy. Median duration of response to a single course of treatment is about 1 year with complete remission rates that last 2 years or longer in about 25% of patients. Clinical trials suggest that anti- CD20 radioimmunotherapy is superior to total body irradiation in patients undergoing stem cell supported therapy for B-cell lymphoma, and that it is a safe and efficacious modality when used as consolidation therapy following chemotherapy. Among cytotoxic treatment options, current evidence suggests that one course of anti-CD20 radioimmunotherapy is as efficacious as six to eight cycles of combination chemotherapy. A major question that persists is how effective these agents are in the setting of rituximab- refractory lymphoma. These products have been underutilised because of the complexity of treatment coordination and concerns regarding reimbursement
Relativistic quantum clocks
The conflict between quantum theory and the theory of relativity is
exemplified in their treatment of time. We examine the ways in which their
conceptions differ, and describe a semiclassical clock model combining elements
of both theories. The results obtained with this clock model in flat spacetime
are reviewed, and the problem of generalizing the model to curved spacetime is
discussed, before briefly describing an experimental setup which could be used
to test of the model. Taking an operationalist view, where time is that which
is measured by a clock, we discuss the conclusions that can be drawn from these
results, and what clues they contain for a full quantum relativistic theory of
time.Comment: 12 pages, 4 figures. Invited contribution for the proceedings for
"Workshop on Time in Physics" Zurich 201
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