Million laserstråler, atomklokker og om naturkonstantene kanskje endres over tid

Fellessemninar ved Institutt for fysikk og teknologi:

Harald Hauglin fra justervesenet gir et seminar over temaet

"A Million Laser Lines, Atomic Clocks and the Possible Drift of Natural Constants"

Sammendrag:

Frequency can be measured with a precision far surpassing that of any other physical quantity. For this reason atomic frequency standards are directly tied to physical realizations of several basal SI units (second, meter, volt) as well as providing the basis for everyday applications such as GPS positioning, high speed synchronized data communication and reliable electrical power distribution.

The current SI second is defined as the duration of 9 192 631 770 cycles of radiation absorbed or emitted in the hyperfine transition of Cs. These cycles can be directly counted, accumulated and displayed using electronic frequency counters, which therefore provide the  clockwork of such ’microwave’ atomic clocks. State-of-the-art Cs clocks have a long term fractional stability of approx. 10^-15 – i.e. drifting no more than a second in 30 million years.

This already astonishing stability is expected to improve by 3 - 4 orders of magnitude with new ’optical’ atomic clocks based on stable lasers locked to narrow atomic transitions. However, directly counting and accumulating optical cycles (typically 500 THz) is far beyond the reach of electronic counters. In my talk I will give an introduction to atomic clocks and stabilized optical frequency combs that provide the necessary clockwork for optical frequency atomic clocks.

The stability of atomic clocks depends ultimately on the time invariance of atomic resonance frequencies, which in turn depend on the strength of the electromagnetic interaction (fine structure) and the strong nuclear force (hyperfine structure). Stable frequency combs enable sensitive comparisons of different atomic clock frequencies over time and may set stringent limits on any current era drift of the natural constants. I will discuss some recent results and point out some of the opportunities for future clock-based experiments probing the ‘constancy’ of natural constants.

Foredraget er åpent for alle interesserte.