30 research outputs found
Observation and cancellation of the dc Stark shift in strontium optical lattice clocks
We report on the observation of a dc Stark frequency shift at the
level by comparing two strontium optical lattice clocks. This frequency shift
arises from the presence of electric charges trapped on dielectric surfaces
placed under vacuum close to the atomic sample. We show that these charges can
be eliminated by shining UV light on the dielectric surfaces, and characterize
the residual dc Stark frequency shift on the clock transition at the
level by applying an external electric field. This study shows that the dc
Stark shift can play an important role in the accuracy budget of lattice
clocks, and should be duly taken into account
Absolute Frequency Measurement of Rubidium 5S-7S Two-Photon Transitions
We report the absolute frequency measurements of rubidium 5S-7S two-photon
transitions with a cw laser digitally locked to an atomic transition and
referenced to an optical frequency comb. The narrow, two-photon transition,
5S-7S (760 nm) insensitive to first order in a magnetic field, is a promising
candidate for frequency reference. The performed tests yield the transition
frequency with accuracy better than reported previously.Comment: This paper was published in Optics Letters and is made available as
an electronic reprint with the permission of OSA. The paper can be found at
http://dx.doi.org/10.1364/OL.38.004581. Systematic or multiple reproduction
or distribution to multiple locations via electronic or other means is
prohibited and is subject to penalties under la
Lattice Induced Frequency Shifts in Sr Optical Lattice Clocks at the Level
We present a comprehensive study of the frequency shifts associated with the
lattice potential for a Sr lattice clock. By comparing two such clocks with a
frequency stability reaching after a one hour integration
time, and varying the lattice depth up to with being the
recoil energy, we evaluate lattice related shifts with an unprecedented
accuracy. We put the first experimental upper bound on the recently predicted
frequency shift due to the magnetic dipole (M1) and electric quadrupole (E2)
interactions. This upper bound is significantly smaller than the theoretical
upper limit. We also give a new upper limit on the effect of
hyperpolarizability with an improvement by more than one order of magnitude.
Finally, we report the first observation of the vector and tensor shifts in a
lattice clock. Combining these measurements, we show that all known lattice
related perturbation will not affect the clock accuracy down to the
level, even for very deep lattices, up to
Matter-Wave Interference versus Spontaneous Pattern Formation in Spinor Bose-Einstein Condensate
We describe effects of matter-wave interference of spinor states in the
Rb Bose-Einstein condensate. The components of the F=2 manifold are
populated by forced Majorana transitions and then fall freely due to gravity in
an applied magnetic field. Weak inhomogeneities of the magnetic field, present
in the experiment, impose relative velocities onto different components,
which show up as interference patterns upon measurement of atomic density
distributions with a Stern-Gerlach imaging method. We show that interference
effects may appear in experiments even if gradients of the magnetic field
components are eliminated but higher order inhomogeneity is present and the
duration of the interaction is long enough. In particular, we show that the
resulting matter-wave interference patterns can mimic spontaneous pattern
formation in the quantum gas.Comment: 5 pages, 4 figures, version accepted in Phys. Rev.
Gene expression of key regulators of mitochondrial biogenesis is sex dependent in mice with growth hormone receptor deletion in liver
Mitochondrial biogenesis is an essential process for cell viability. Mice with disruption of the growth hormone receptor (GHR) gene (Ghr gene) in the liver (LiGHRKO), in contrast to long-lived mice with global deletion of the Ghr gene (GHRKO), are characterized by lack of improved insulin sensitivity and severe hepatic steatosis. Tissue-specific disruption of the GHR in liver results in a mouse model with dramatically altered GH/IGF1 axis. We have previously shown increased levels of key regulators of mitochondrial biogenesis in insulin-sensitive GHRKO mice. The aim of the present study is to assess, using real-time PCR, the gene expression of key regulators of mitochondrial biogenesis (Pgc1 alpha, Ampk, Sirt1, Nrf2 and Mfn2) and a marker of mitochondrial activity (CoxIV) in brains, kidneys and livers of male and female LiGHRKO and wild-type (WT) mice. There were significant differences between males and females. In the brain, expression of Pgc1 alpha, Ampk, Sirt1, Nrf2 and Mfn2 was lower in pooled females compared to pooled males. In the kidneys, expression of Ampk and Sirt1 was also lower in female mice. In the liver, no differences between males and females were observed. Sexual dimorphism may play an important role in regulating the biogenesis of mitochondria
Gene expression of key regulators of mitochondrial biogenesis is sex dependent in mice with growth hormone receptor deletion in liver
Abstract: Mitochondrial biogenesis is an essential process for cell viability. Mice with disruption of the growth hormone receptor (GHR) gene (Ghr gene) in the liver (LiGHRKO), in contrast to long-lived mice with global deletion of the Ghr gene (GHRKO), are characterized by lack of improved insulin sensitivity and severe hepatic steatosis. Tissue-specific disruption of the GHR in liver results in a mouse model with dramatically altered GH/IGF1 axis. We have previously shown increased levels of key regulators of mitochondrial biogenesis in insulin-sensitive GHRKO mice. The aim of the present study is to assess, using real-time PCR, the gene expression of key regulators of mitochondrial biogenesis (Pgc1α, Ampk, Sirt1, Nrf2 and Mfn2) and a marker of mitochondrial activity (CoxIV) in brains, kidneys and livers of male and female LiGHRKO and wild-type (WT) mice. There were significant differences between males and females. In the brain, expression of Pgc1α, Ampk, Sirt1, Nrf2 and Mfn2 was lower in pooled females compared to pooled males. In the kidneys, expression of Ampk and Sirt1 was also lower in female mice. In the liver, no differences between males and females were observed. Sexual dimorphism may play an important role in regulating the biogenesis of mitochondria
Guidelines for developing optical clocks with 10-18 fractional frequency uncertainty
There has been tremendous progress in the performance of optical frequency standards since the first proposals to carry out precision spectroscopy on trapped, single ions in the 1970s. The estimated fractional frequency uncertainty of today's leading optical standards is currently in the 10−18 range, approximately two orders of magnitude better than that of the best caesium primary frequency standards. This exceptional accuracy and stability is resulting in a growing number of research groups developing optical clocks. While good review papers covering the topic already exist, more practical guidelines are needed as a complement. The purpose of this document is therefore to provide technical guidance for researchers starting in the field of optical clocks. The target audience includes national metrology institutes (NMIs) wanting to set up optical clocks (or subsystems thereof) and PhD students and postdocs entering the field. Another potential audience is academic groups with experience in atomic physics and atom or ion trapping, but with less experience of time and frequency metrology and optical clock requirements. These guidelines have arisen from the scope of the EMPIR project "Optical clocks with 1×10−18 uncertainty" (OC18). Therefore, the examples are from European laboratories even though similar work is carried out all over the world. The goal of OC18 was to push the development of optical clocks by improving each of the necessary subsystems: ultrastable lasers, neutral-atom and single-ion traps, and interrogation techniques. This document shares the knowledge acquired by the OC18 project consortium and gives practical guidance on each of these aspects.EU/Horizon2020/EMPIR/E
Comparison of two Strontium optical lattice clocks in agreement at the 10−16 level
International audienc
Comparison of two Strontium optical lattice clocks in agreement at the 10−16 level
International audienc