Optical frequency metrology

Abstract

Extremely narrow optical resonances in cold atoms or single trapped ions can be measured with high resolution. A laser locked to such a narrow optical resonance could serve as a highly stable oscillator for an all-optical atomic clock. However, until recently there was no reliable clockwork mechanism that could count optical frequencies of hundreds of terahertz. Techniques using femtosecond-laser frequency combs, developed within the past few years, have solved this problem. The ability to count optical oscillations of more than 1015 cycles per second facilitates high-precision optical spectroscopy, and has led to the construction of an all-optical atomic clock that is expected eventually to outperform today's state-of-the-art caesium clocks.

Frequency comb assisted diode laser spectroscopy for measurement of microcavity dispersion

“…The total bandwidth of these combs is limited by the dispersion of the microcavity, which render the resonator modes nonequidistant. Thus, understanding and measurement of microcavity dispersion is an essential step towards octave spanning comb generation in microcavities, required to implement self referencing [1,16]. The dispersion of microcavities leads to a walk-off between subsequent free spectral ranges (FSRs) of a microcavity and is expected to be smaller than 1 MHz/FSR (cf.…”

“…Another approach has been the idea of imprinting the accuracy of an optical frequency comb to a transfer laser with higher intensity, which is already utilized since the first spectroscopy experiments with frequency combs and enabling determination of transition frequencies of sin-gle atomic and molecular resonances with unprecedented accuracy [1,9]. While in this scheme, the transfer laser has to remain phase locked to a frequency comb or high finesse cavity, the latter makes it challenging to perform measurements over a large bandwidth within short timescales [10,11].…”

“…Within the last decade, the invention of the optical frequency comb has revolutionized the field of spectroscopy and allowed measurements with previously unattainable precision [1,2,3]. However, despite significant advances [4,5,6,7,8], the use of frequency combs for precise broadband spectroscopy has remained challenging owing to low optical power per comb line and the difficulty to resolve features that are smaller than the combs free spectral range.…”

Absolute frequency determination of molecular transition in the Doppler regime at kHz level of accuracy

“…An 88 Sr optical atomic lattice clock [12,13] served as a frequency reference in most of the performed measurements. The spectrometer was optically linked to the optical atomic clock via the OFC [14,15]. Such a reference has significant advantages over typically used radio frequency (RF) references in terms of stability and accuracy.…”

Data-processing inequalities for quantum metrology

“…Quantum metrology refers to the study of the ultimate limits in the accuracy of estimates given the structure imposed by quantum theory [1,2]. Estimation at or near this limit is important for practical objectives such as improving time and frequency standards [3,4] as well as fundamental physics, such as the detection of gravitational waves [5].Researchers have found many novel approaches to quantum metrology using, for example, multipass interferometers [6], machine learning techniques [7], and computational Bayesian statistics [8] as well as new bounds [9,10] in increasingly more general scenarios. Here we supplement these results with one of a different flavor.…”