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Register a new userDevelopment of a strontium optical lattice clock for the SOC mission on the ISS
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Ultra-precise optical clocks in space will allow new studies in fundamental physics and astronomy. Within an European Space Agency (ESA) program, the Space Optical Clocks (SOC) project aims to install and to operate an optical lattice clock on the International Space Station (ISS) towards the end of this decade. It would be a natural follow-on to the ACES mission, improving its performance by at least one order of magnitude. The payload is planned to include an optical lattice clock, as well as a frequency comb, a microwave link, and an optical link for comparisons of the ISS clock with ground clocks located in several countries and continents. Within the EU-FP7-SPACE-2010-1 project no. 263500, during the years 2011-2015 a compact, modular and robust strontium lattice optical clock demonstrator has been developed. Goal performance is a fractional frequency instability below 1x10^{-15}, tau^{-1/2} and a fractional inaccuracy below 5x10^{-17}. Here we describe the current status of the apparatus development, including the laser subsystems. Robust preparation of cold {88}^Sr atoms in a second stage magneto-optical trap (MOT) is achieved.
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The ESA mission Space Optical Clock project aims at operating an optical lattice clock on the ISS in approximately 2023. The scientific goals of the mission are to perform tests of fundamental physics, to enable space-assisted relativistic geodesy and to intercompare optical clocks on the ground using microwave and optical links. The performance goal of the space clock is less than $1 times 10^{-17}$ uncertainty and $1 times 10^{-15} {tau}^{-1/2}$ instability. Within an EU-FP7-funded project, a strontium optical lattice clock demonstrator has been developed. Goal performances are instability below $1 times 10^{-15} {tau}^{-1/2}$ and fractional inaccuracy $5 times 10^{-17}$. For the design of the clock, techniques and approaches suitable for later space application are used, such as modular design, diode lasers, low power consumption subunits, and compact dimensions. The Sr clock apparatus is fully operational, and the clock transition in $^{88}$Sr was observed with linewidth as small as 9 Hz.
We report on a transportable optical clock, based on laser-cooled strontium atoms trapped in an optical lattice. The experimental apparatus is composed of a compact source of ultra-cold strontium atoms including a compact cooling laser set-up and a transportable ultra-stable laser for interrogating the optical clock transition. The whole setup (excluding electronics) fits within a volume of less than 2 m$^3$. The high degree of operation reliability of both systems allowed the spectroscopy of the clock transition to be performed with 10 Hz resolution. We estimate an uncertainty of the clock of $7times10^{-15}$.
We report on the realization of a magneto-optical trap (MOT) for metastable strontium operating on the 2.92 $mu$m transition between the energy levels $5s5p~^3mathrm{P}_2$ and $5s4d~^3mathrm{D}_3$. The strontium atoms are initially captured in a MOT operating on the 461 nm transition between the energy levels $5s^2~^1mathrm{S}_0$ and $5s5p~^1mathrm{P}_1$, prior to being transferred into the metastable MOT and cooled to a final temperature of 6 $mu$K. Challenges arising from aligning the mid-infrared and 461 nm light are mitigated by employing the same pyramid reflector to realize both MOTs. Finally, the 2.92 $mu$m transition is used to realize a full cooling sequence for an optical lattice clock, in which cold samples of $^{87}mathrm{Sr}$ are loaded into a magic-wavelength optical lattice and initialized in a spin-polarized state to allow high-precision spectroscopy of the $5s^2~^1mathrm{S}_0$ to $5s5p~^3mathrm{P}_0$ clock transition.
The new strontium atomic clock at INRIM seeks to establish a new frontier in quantum measurement by joining state-of-the-art optical lattice clocks and the quantized electromagnetic field provided by a cavity QED setup. The goal of our experiment is to apply advanced quantum techniques to state-of-the-art optical lattice clocks, demonstrating enhanced sensitivity while preserving long coherence times and the highest accuracy. In this paper we describe the current status of the experiment and the prospected sensitivity gain for the designed cavity QED setup.
We demonstrate the absence of a DC Stark shift in an ytterbium optical lattice clock. Stray electric fields are suppressed through the introduction of an in-vacuum Faraday shield. Still, the effectiveness of the shielding must be experimentally assessed. Such diagnostics are accomplished by applying high voltage to six electrodes, which are grounded in normal operation to form part of the Faraday shield. Our measurements place a constraint on the DC Stark shift at the $10^{-20}$ level, in units of the clock frequency. Moreover, we discuss a potential source of error in strategies to precisely measure or cancel non-zero DC Stark shifts, attributed to field gradients coupled with the finite spatial extent of the lattice-trapped atoms. With this consideration, we find that Faraday shielding, complemented with experimental validation, provides both a practically appealing and effective solution to the problem of DC Stark shifts in optical lattice clocks.
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