340 research outputs found
Deterministic quantum state transfer of atoms in a random magnetic field
We propose a method for transferring atoms to a target quantum state for a
multilevel quantum system with sequentially increasing, but otherwise unknown,
energy splitting. This is achieved with a feedback algorithm that processes
off-resonant optical measurements of state populations during adiabatic rapid
passage in real-time. Specifically, we reliably perform the transfer
for a
sample of ultracold Rb in the presence of a random external magnetic
field
Deep rest-frame far-UV spectroscopy of the giant Lyman-alpha emitter 'Himiko'
We present deep 10h VLT/XSHOOTER spectroscopy for an extraordinarily luminous
and extended Lya emitter at z=6.595 referred to as Himiko and first discussed
by Ouchi et al. (2009), with the purpose of constraining the mechanisms
powering its strong emission. Complementary to the spectrum, we discuss NIR
imaging data from the CANDELS survey. We find neither for HeII nor any metal
line a significant excess, with 3 sigma upper limits of 6.8, 3.1, and
5.8x10^{-18} erg/s/cm^2 for CIV 1549, HeII 1640, CIII]
1909, respectively, assuming apertures with 200 km/s widths and offset
by -250 km/s w.r.t to the peak Lya redshift. These limits provide strong
evidence that an AGN is not a major contribution to Himiko's Lya flux. Strong
conclusions about the presence of PopIII star-formation or gravitational
cooling radiation are not possible based on the obtained HeII upper limit. Our
Lya spectrum confirms both spatial extent and flux (8.8+/-0.5x10^{-17}
erg/s/cm^2) of previous measurements. In addition, we can unambiguously exclude
any remaining chance of it being a lower redshift interloper by significantly
detecting a continuum redwards of Lya, while being undetected bluewards
Strong zero-field F\"orster resonances in K-Rb Rydberg systems
We study resonant dipole-dipole coupling and the associated van der Waals
energy shifts in Rydberg excited atomic rubidium and potassium and investigate
F\"orster resonances between interspecies pair states. A comprehensive survey
over experimentally accessible pair state combinations reveals multiple
candidates with small F\"orster defects. We crucially identify the existence of
an ultrastrong, "low" electric field K-Rb F\"orster resonance with a extremely
large zero-field crossover distance exceeding 100 m between the van der
Waals regime and the resonant regime. This resonance allows for a strong
interaction over a wide range of distances and by investigating its dependence
on the strength and orientation of external fields we show this to be largely
isotropic. As a result, the resonance offers a highly favorable setting for
studying long-range resonant excitation transfer and entanglement generation
between atomic ensembles in a flexible geometry. The two-species K-Rb system
establishes a unique way of realizing a Rydberg single-photon optical
transistor with a high-input photon rate and we specifically investigate an
experimental scheme with two separate ensembles
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