Miniature single-ion optical clock

Since 1967, the second is defined with respect to an atomic transition. More precisely, the second is determined in relation to 9 192 631 770 periods of the radiation corresponding to two hyperfine states of the ground state of an unperturbed Cesium 133 atom. Today, the most efficient atomic clocks are in the optical domain: a laser is used to interrogate the transition of an atomic reference. The atomic elements used are for example strontium, mercury or ytterbium. Other optical clocks exploit a single trapped ion to establish a frequency reference. The best optical clocks occupy volumes of several thousand liters. Although there are fiber networks disseminating optical references between different laboratories, the need to be able to transport clocks remains a major issue for fundamental physics or for other applications such as geodesy. The Time and Frequency department of FEMTO-ST is developing a transportable optical clock with Yb+ trapped ion. The objective of this project is to obtain a total volume of the experiment of 500 L with performances ten times higher than current compact clocks. A single ion is trapped with the help of electric fields generated by a chip constituting a Paul surface trap. A single laser beam allows its cooling in the three directions of space. A laser with a wavelength of about 435.5 nm is used to interrogate the ion and form an ultra-stable oscillator. To trap ions, a prototype copper trap on FR-4 was used while in parallel a trap was designed and fabricated within the department. The rapid confinement of ions with the prototype trap allowed us to set up the experimental system and establish our first results. Measurements characterizing the trap could be performed and experimental techniques for the control of the trap were set up. The clock laser requires a pre-stabilization for its frequency noise reduction. Its frequency lock on an ultra-stable cavity operating at a telecom wavelength has been achieved using an optical frequency comb. Different simulations have been performed to predict the relative frequency stability of the clock or the behavior of the new trap.

laser cooling, atomic clock, time and frequency metrology, trapped ions

Full document (FR) : TEL-04195089