604 research outputs found
Gravitational Collapse of Gravitational Waves in 3D Numerical Relativity
We demonstrate that evolutions of three-dimensional, strongly non-linear
gravitational waves can be followed in numerical relativity, hence allowing
many interesting studies of both fundamental and observational consequences. We
study the evolution of time-symmetric, axisymmetric {\it and} non-axisymmetric
Brill waves, including waves so strong that they collapse to form black holes
under their own self-gravity. The critical amplitude for black hole formation
is determined. The gravitational waves emitted in the black hole formation
process are compared to those emitted in the head-on collision of two Misner
black holes.Comment: 4 page
The Shapiro Conjecture: Prompt or Delayed Collapse in the head-on collision of neutron stars?
We study the question of prompt vs. delayed collapse in the head-on collision
of two neutron stars. We show that the prompt formation of a black hole is
possible, contrary to a conjecture of Shapiro which claims that collapse is
delayed until after neutrino cooling. We discuss the insight provided by
Shapiro's conjecture and its limitation. An understanding of the limitation of
the conjecture is provided in terms of the many time scales involved in the
problem. General relativistic simulations in the Einstein theory with the full
set of Einstein equations coupled to the general relativistic hydrodynamic
equations are carried out in our study.Comment: 4 pages, 7 figure
High-fidelity single-shot readout for a spin qubit via an enhanced latching mechanism
The readout of semiconductor spin qubits based on spin blockade is fast but
suffers from a small charge signal. Previous work suggested large benefits from
additional charge mapping processes, however uncertainties remain about the
underlying mechanisms and achievable fidelity. In this work, we study the
single-shot fidelity and limiting mechanisms for two variations of an enhanced
latching readout. We achieve average single-shot readout fidelities > 99.3% and
> 99.86% for the conventional and enhanced readout respectively, the latter
being the highest to date for spin blockade. The signal amplitude is enhanced
to a full one-electron signal while preserving the readout speed. Furthermore,
layout constraints are relaxed because the charge sensor signal is no longer
dependent on being aligned with the conventional (2, 0) - (1, 1) charge dipole.
Silicon donor-quantum-dot qubits are used for this study, for which the dipole
insensitivity substantially relaxes donor placement requirements. One of the
readout variations also benefits from a parametric lifetime enhancement by
replacing the spin-relaxation process with a charge-metastable one. This
provides opportunities to further increase the fidelity. The relaxation
mechanisms in the different regimes are investigated. This work demonstrates a
readout that is fast, has one-electron signal and results in higher fidelity.
It further predicts that going beyond 99.9% fidelity in a few microseconds of
measurement time is within reach.Comment: Supplementary information is included with the pape
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