11,614 research outputs found
Coherent Collisions between Bose-Einstein Condensates
We study the non-degenerate parametric amplifier for matter waves,
implemented by colliding two Bose-Einstein condensates. The coherence of the
amplified waves is shown by observing high contrast interference with a
reference wave and by reversing the amplification process. Since our
experiments also place limits on all known sources of decoherence, we infer
that relative number squeezing is most likely present between the amplified
modes. Finally, we suggest that reversal of the amplification process may be
used to detect relative number squeezing without requiring single-particle
detection.Comment: 4.2 pages, 4 figures, please take postscript version for best quality
of picture
Process migration in UNIX environments
To support process migration in UNIX environments, the main problem is how to encapsulate the location dependent features of the system in such a way that a host independent virtual environment is maintained by the migration handlers on the behalf of each migrated process. An object-oriented approach is used to describe the interaction between a process and its environment. More specifically, environmental objects were introduced in UNIX systems to carry out the user-environment interaction. The implementation of the migration handlers is based on both the state consistency criterion and the property consistency criterion
Correctness criteria for process migration
Two correctness criteria, the state consistency criterion and the property consistency criterion for process migration are discussed. The state machine approach is used to model the interactions between a user process and its environment. These criteria are defined in terms of the model. The idea of environment view was introduced to distinguish what a user process observes about its environment from what its environment state really is and argue that a consistent view of the environment must be maintained for every migrating process
Amortised resource analysis with separation logic
Type-based amortised resource analysis following Hofmann and Jostāwhere resources are associated with individual elements of data structures and doled out to the programmer under a linear typing disciplineāhave been successful in providing concrete resource bounds for functional programs, with good support for inference. In this work we translate the idea of amortised resource analysis to imperative languages by embedding a logic of resources, based on Bunched Implications, within Separation Logic. The Separation Logic component allows us to assert the presence and shape of mutable data structures on the heap, while the resource component allows us to state the resources associated with each member of the structure. We present the logic on a small imperative language with procedures and mutable heap, based on Java bytecode. We have formalised the logic within the Coq proof assistant and extracted a certified verification condition generator. We demonstrate the logic on some examples, including proving termination of in-place list reversal on lists with cyclic tails
Experimental and analytical investigation of the variation of spray characteristics along a radial distance downstream of a pressure-swirl atomizer
The variation of spray characteristics along a radial distance downstream of a pressure-swirl atomizer was measured by laser light-scattering technology. An analytical model was developed to predict the variation of spray characteristics along the radial distance. A comparison of the predicted and experimental data showed excellent agreement. Therefore, the spray model proposed, although relatively simple, is correct and can be used, with some expansion and modification of the prepared model, to predict more complicated spray systems
Dissociation and Decay of Ultra-cold Sodium Molecules
The dissociation of ultracold molecules is studied by ramping an external
magnetic field through a Feshbach resonance. The observed dissociation energy
shows non-linear dependence on the ramp speed and directly yields the strength
of the atom-molecule coupling. In addition, inelastic molecule-molecule and
molecule-atom collisions are characterized
A study of the effects of environmental and ablator performance uncertainties on heat shielding requirements for hyperbolic entry vehicles. Volume 2 - Summary of calculations
Calculated ablative quantities for nylon phenolic heat shielding materials of hyperbolic reentry vehicle
Impact of the Casimir-Polder Potential and Johnson Noise on Bose-Einstein Condensate Stability near Surfaces
We investigate the stability of magnetically trapped atomic Bose-Einstein
condensates and thermal clouds near the transition temperature at small
distances 0.5 microns < d < 10 microns from a microfabricated silicon chip. For
a 2 microns thick copper film the trap lifetime is limited by Johnson-noise
induced currents and falls below 1 s at a distance of 4 microns. A dielectric
surface does not adversely affect the sample until the attractive
Casimir-Polder potential significantly reduces the trap depth.Comment: 4 pages, 5 figures, and submitted to Physical Review Letter
Ultracold molecules: vehicles to scalable quantum information processing
We describe a novel scheme to implement scalable quantum information
processing using Li-Cs molecular state to entangle Li and Cs
ultracold atoms held in independent optical lattices. The Li atoms will
act as quantum bits to store information, and Cs atoms will serve as
messenger bits that aid in quantum gate operations and mediate entanglement
between distant qubit atoms. Each atomic species is held in a separate optical
lattice and the atoms can be overlapped by translating the lattices with
respect to each other. When the messenger and qubit atoms are overlapped,
targeted single spin operations and entangling operations can be performed by
coupling the atomic states to a molecular state with radio-frequency pulses. By
controlling the frequency and duration of the radio-frequency pulses,
entanglement can either be created or swapped between a qubit messenger pair.
We estimate operation fidelities for entangling two distant qubits and discuss
scalability of this scheme and constraints on the optical lattice lasers
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