94 research outputs found
A momentum filter for atomic gas
We propose and demonstrate a momentum filter for atomic gas based on a
designed Talbot-Lau interferometer. It consists in two identical optical
standing wave pulses separated by a delay equal to odd multiples of the half
Talbot time. The one dimensional momentum width along the long direction of a
cigar shape condensate is rapidly and greatly purified to a minimum, which
corresponds to the ground state energy of the confining trap in our experiment.
We find good agreement between theoretical analysis and experimental results.
The filter is also effective for non-condensed cold atoms and could be applied
widely.Comment: 9 pages, 6 figures, accepted by New Journal of Physic
The observation of diffraction phases in matter wave scattering
We study the diffraction phase of different orders via the Dyson expansion
series, for ultracold atomic gases scattered by a standing-wave pulse. As these
diffraction phases are not observable in a single pulse scattering process, a
temporal Talbot-Lau interferometer consisting of two standing-wave pulses is
demonstrated experimentally with a Bose-Einstein condensate to explore this
physical effect. The role of the diffraction phases is clearly shown by the
second standing-wave pulse in the relative population of different momentum
states. Our experiments demonstrate obvious effects beyond the Raman-Nath
method, while agree well with our theory by including the diffraction phases.
In particular, the observed asymmetry in the dependence of the relative
population on the interval between two standing-wave pulses reflects the
diffraction phase differences. The role of interatomic interaction in the
Talbot-Lau interferometer is also discussed.Comment: 7 pages, 3 figures, accepted by Phys. Rev.
Effective preparation and collisional decay of atomic condensate in excited bands of an optical lattice
We present a method for the effective preparation of a Bose-Einstein
condensate (BEC) into the excited bands of an optical lattice via a
standing-wave pulse sequence. With our method, the BEC can be prepared in
either a single Bloch state in a excited-band, or a coherent superposition of
states in different bands. Our scheme is experimentally demonstrated by
preparing a Rb BEC into the -band and the superposition of - and
-band states of a one-dimensional optical lattice, within a few tens of
microseconds. We further measure the decay of the BEC in the -band state,
and carry an analytical calculation for the collisional decay of atoms in the
excited-band states. Our theoretical and experimental results consist well.Comment: 9 pages, 5 figures, Accepted by Phys. Rev.
Productive Development of Scalable Network Functions with NFork
Despite decades of research, developing correct and scalable concurrent
programs is still challenging. Network functions (NFs) are not an exception.
This paper presents NFork, a system that helps NF domain experts to
productively develop concurrent NFs by abstracting away concurrency from
developers. The key scheme behind NFork's design is to exploit NF
characteristics to overcome the limitations of prior work on concurrency
programming. Developers write NFs as sequential programs, and during runtime,
NFork performs transparent parallelization by processing packets in different
cores. Exploiting NF characteristics, NFork leverages transactional memory and
develops efficient concurrent data structures to achieve scalability and
guarantee the absence of concurrency bugs.
Since NFork manages concurrency, it further provides (i) a profiler that
reveals the root causes of scalability bottlenecks inherent to the NF's
semantics and (ii) actionable recipes for developers to mitigate these root
causes by relaxing the NF's semantics. We show that NFs developed with NFork
achieve competitive scalability with those in Cisco VPP [16], and NFork's
profiler and recipes can effectively aid developers in optimizing NF
scalability.Comment: 16 pages, 8 figure
Relaxation of Bosons in One Dimension and the Onset of Dimensional Crossover
We study ultra-cold bosons out of equilibrium in a one-dimensional (1D)
setting and probe the breaking of integrability and the resulting relaxation at
the onset of the crossover from one to three dimensions. In a quantum Newton's
cradle type experiment, we excite the atoms to oscillate and collide in an
array of 1D tubes and observe the evolution for up to 4.8 seconds (400
oscillations) with minimal heating and loss. By investigating the dynamics of
the longitudinal momentum distribution function and the transverse excitation,
we observe and quantify a two-stage relaxation process. In the initial stage
single-body dephasing reduces the 1D densities, thus rapidly drives the 1D gas
out of the quantum degenerate regime. The momentum distribution function
asymptotically approaches the distribution of quasimomenta (rapidities), which
are conserved in an integrable system. In the subsequent long time evolution,
the 1D gas slowly relaxes towards thermal equilibrium through the collisions
with transversely excited atoms. Moreover, we tune the dynamics in the
dimensional crossover by initializing the evolution with different imprinted
longitudinal momenta (energies). The dynamical evolution towards the relaxed
state is quantitatively described by a semiclassical molecular dynamics
simulation.Comment: 32 pages, 14 figures. Minor changes are made according to the Referee
report
- …