In 2013, for the first time ever, a many-atom optical lattice clock surpassed single ion clocks as the most stable, and accurate frequency standard in existence. Since this first result, continued improvements to the clock's accuracy and stability have been made. This work will focus on two of these major improvements. Firstly the frequency uncertainty was brought down to 2.5*10^-18, thanks in part to an accurate determination of the black body radiation shift, based on better characterization of the level structure of 87Sr. Secondly, a control modification will be demonstrated which provides 20% reduction in the standard deviation for the clock's frequency under differential measurement schemes. This represents a new record for clock accuracy, pushing performance towards the 10^-19 level.
In 2013, for the first time ever, a many-atom optical lattice clock surpassed single ion clocks as the most stable, and accurate frequency standard in existence. Since this first result, continued improvements to the clock's accuracy and stability have been made. This work will focus on two of these major improvements. Firstly the frequency uncertainty was brought down to 2.5*10^-18, thanks in part to an accurate determination of the black body radiation shift, based on better characterization of the level structure of 87Sr. Secondly, a control modification will be demonstrated which provides 20% reduction in the standard deviation for the clock's frequency under differential measurement schemes. This represents a new record for clock accuracy, pushing performance towards the 10^-19 level.
Clocks based on optical transitions in ions and atoms are quickly moving to the forefront of the frequency standards field mainly because of the high spec-tral resolution, and therefore the potential stability and accuracy, which can be achieved. In this thesis a new optical clock based on neutral atoms trapped in an optical lattice is presented, demonstrating spectroscopy of the clock transition free of any lineshape or accuracy degradation due to atomic motion. The system simu-lates a single trapped ion clock, but allows use of thousands of atoms for improved signal to noise ratio, and clock stability. High accuracy can also be achieved as the lattice can be designed to shift the energy of the two atomic clock states equally, such that the transition frequency is unchanged. Strontium is a natural candidate for such a clock as it offers an extremely narrow optical transition (∼1 mHz) based on atomic states which are very insensitive to external fields. The strontium level structure allows efficient laser cooling to 1 µK with diode laser sources, and a con-venient wavelength of 813 nm for the zero-differential Stark shift optical lattice. The strontium lattice clock system has allowed observation of high signal-to-noise
The exquisite control exhibited over quantum states of individual particles has revolutionized the field of precision measurement, as exemplified by the most accurate atomic clock realized in single trapped ions. Whereas many-atom lattice clocks have shown advantages in measurement precision over trapped-ion clocks, their accuracy has remained 20 times worse. Here we demonstrate, for the first time, that a many-atom system achieves accuracy (6x10^{-18}) better than a single ion-based clock, with vastly reduced averaging times (3000 s). This is the first time a single clock has achieved the best performance in all three key ingredients necessary for consideration as a primary standard - stability, reproducibility, and accuracy. This work paves the way for future experiments to integrate many-body quantum state engineering into the frontiers of quantum metrology, creating exciting opportunities to advance precision beyond the standard quantum limit. Improved frequency standards will have impact to a wide range of fields from the realization of the SI units, the development of quantum sensors, to precision tests of the fundamental laws of nature.
Optical clocks are being developed worldwide and are at the forefront of frequency metrology. Today they outperform microwave clocks instability and inaccuracy by two orders of magnitude, raising discussion about the redefinition of the SI second. Their outstanding performances are paving the way to applications in different fields apart from metrology. Optical clocks can be used for geodetic measurements, such as chronometric levelling, and fundamental physics experiments. These applications require transportable, and even space-born optical clocks that are in development. Space optical clocks will serve as a high accurate references for intercontinental clock comparisons, and will also provide a unique test bench for fundamental physics theories, such as Einstein’s prediction of time dilation and equivalence principle.
This work presents the development and characterization of a transportable strontium optical lattice clock, realised in the framework of the ESA I-SOC (Space Optical Clock on the ISS) mission. The aim of the project is to investigate new technologies and techniques, in order to develop a robust apparatus as demonstrator for space applications. Special effort has been made to reduce the size and weight of the clock, so as to meet the stringent requirements of a space mission. The system reported here is one of the most compact optical clock to date, with a total volume of only 1 m3, excluding electronics.
The clock is operated with the strontium bosonic isotope 88Sr: this is preferable to the fermionic counterpart 87Sr, commonly used in optical lattice clocks, if simplicity and reliability are required. However, in terms of accuracy, bosonic clocks present some disadvantages compared with the fermionic ones, which have significantly slowed down their development for metrological applications.
We characterised the relevant operating parameters and their effect on the clock accuracy and instability. Exploiting a clock laser offering an outstanding stability, we were able to demonstrate a clock fractional instability of 3×10-18 , and an inaccuracy of 2×10-17: both values represent a factor of 30 improvement compared with previous works on bosonic optical clocks. These results suggest that, in the near future, bosonic clocks may become competitive to their fermionic counterparts. This is of interest for applications such as time scale realization, transportable clocks, or for test of fundamental physics. As an example, we measured the 88Sr-87Sr isotope shift, with an uncertainty of 12 mHz.
We describe recent experimental progress with the JILA Sr optical frequency standard, which has a systematic uncertainty at the 10-16fractional frequency level, currently limited by frequency shifts due to atomic interactions and room temperature blackbody radiation (BBR). We will discuss systematic measurements of collisional shifts and provide a complete theory to understand these interaction effects at the 10-17level. We will also discuss plans to interrogate atoms inside a cryogenic shield region to eliminate BBR shifts. We will present our recent successful efforts in improving the laser stability with the aim for the JILA Sr standard to reach the standard quantum measurement limit and achieve record levels of stability. Finally, a second Sr optical lattice clock has been constructed at JILA, and we will discuss the results of intercomparison experiments between the two standards.
This thesis presents the latest achievements regarding the Sr optical lattice clock experiment at LNE-SYRTE, Observatoire de Paris. After having described the general principles for optical lattice clocks and the operation of the clock in question, the emphasis is put on the features that have been added to the experiment since 2007. The most important new elements are an ultra-stable reference cavity for the clock laser, the development of a non-destructive detection technique, and the construction of a second Sr lattice clock. The ultra-stable cavity is constructed from a ULE spacer and fused silica mirrors and has shown a thermal noise floor at 6.5E-16, placing it among the best in the world. The non-destructive detection is effectuated by a phase measurement of a weak probe beam that traverses the atoms placed in one arm of a Mach-Zender interferometer. The non-destructive aspect enables a recycling of the atoms from cycle to cycle which consequently increases the duty cycle, allowing for an increase of the stability of the clock. With these new tools the frequency stability is expected to be 2.2E-16/tau^(1/2) for an optimized sequence. The most recent comparisons between the two Sr clocks reach an accuracy level of 1E-16 after about 1000 s, and this way we have been able to characterize lattice related frequency shifts with an unprecedented accuracy. The measurements ensure a control of lattice related effects at the 1E-18 level even for trap depths as large as 50 Er.
Since 1967, the Second has been defined by the CGPM as 9,192,631,770 periods of oscillation corresponding to a transition between two hyperfine levels in a Cesium atom with zero external fields. Key to this definition was the fact that as experimentalists found new and more precise ways to measure this frequency, the definition of the second would become more and more accurate with time. However, in the last 30 years, new technologies based on tunable lasers addressing optical transitions in atoms, ions, and molecules have offered an entirely new approach to defining the Second with significantly higher precision and accuracy. Here, I will show that by trapping thousands of atoms inside a specially engineered optical lattice one can create an extremely accurate frequency standard with 2 orders of magnitude improvement over current Cs standards. Furthermore, I will explain that standards based on this technology are fundamentally more stable than the primary standard by 3 orders of magnitude. Leapfrogging the currently held accuracy records of ion clocks, this work documents the first optical lattice clock to best all other atomic clock implementations, a mere 8 years after the first proof of principle experiments. In this thesis I will describe how we have overcome a number of important systematic uncertainties to achieve these results. This revolution in accuracy and precision opens the door for new experiments utilizing the clock as a probe of quantum many-body physics. To this end, a new apparatus has been designed that combines the unprecedented precision of clock experiments with the amazing progress attained in quantum gas experiments.