To obtain the most accurate information about the internal structure of atoms and molecules, the best way is to use a resonant laser to excite them. But this laser needs to exceed a certain intensity, which will cause significant changes to the electron shell inside the atoms. According to the physicist organization network on November 23 (Beijing time), scientists at the German Federal Institute of Physics and Technology (PTB) proved through experiments how to prevent this "light shift" phenomenon and proved what the previous theory predicted "Super" Ramsey inspired existence. Related papers were published in the recently published "Physical Review Letters".
"Light shift" means that the position of the atomic level is changed by a strong laser, and the shift depends on the density and wavelength of the emitted laser. If you want to see the atomic properties without quantum shifts, you must avoid "light shifts" or correct them. For the first time, PTB scientists used a series of selected laser pulses to excite atoms in the experiment, eliminating the optical shift effect.
Norman Ramsey proposed to use pulsed radiation to perform accurate measurements, and developed an ultra-precision cesium atomic clock and won the 1989 Nobel Prize. The information contained in the Ramsey excitation is in a hidden state during the emission of two lasers, so the atom can be regarded as the average position between the occurrence of light shift and the absence of light shift. Theoretically, it is possible to correct the light shift by changing the laser frequency, but from a practical point of view, this is not the case, because people cannot know information about the atom shift in advance. Until 2010, someone proposed a method called "super" Ramsey excitation to solve this problem.
The research team confirmed the theory through experiments for the first time. In the "super" Ramsey excitation, during the "dark" period between the two lasers, a third beam with the same density and frequency but opposite phase is introduced. This third laser automatically compensates for possible errors. These errors come from inaccurate estimates of the magnitude of the light shift, small differences in light pulse intensity, and so on.
If the "super" Ramsey excitation of the atomic transition can be achieved, extremely small frequency differences can be detected while showing large light shifts. The research team experimentally proved the theoretical prediction of "super" Ramsey excitation, and obtained 10,000 times the light shift suppression. The researchers pointed out that this eliminates obstacles for making more accurate optical ytterbium atomic clocks, and this method is also very useful in areas that require precise control of the interaction between atoms and lasers, such as quantum information processing.
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