Future clocks will be more precise as a result of reduction in shot noise

Researchers have conquered shot noise limit. It is a fundamental limit in precise determination of internal oscillation frequency of the cesium atom used in atomic clocks. Internal oscillation frequency of the cesium atom is changed to the clicks of a second and is used in our daily time since 1960.

This study has been done by the researchers at Cluster of Excellence QUEST (Centre of Quantum Engineering and Space-Time Research) at Leibniz Universität Hannover, Germany, in collaboration with scientists from Spain, Italy and Denmark and is published online on October 13th issue of the journal Science.

In an atomic clock, there is an oscillation of atoms between two internal states and these oscillations are to be counted for determination of time. As there are two states, the atom behaves more like an individual dice that can be measured in one of two positions with even or odd results. In a particular number of throws, there are chances of 50% even or 50% odd outcomes but small deviations from these results are referred to as shot noise. These deviations of shot noise can be removed by entanglement of atoms at quantum level. If two atoms are entangled and if this entangled pair is thrown than there will always be equal numbers of odd or even outcomes and the shot noise deviations will be removed.

Paired dice with one showing odd and the other even result at a time
Paired dice with one showing odd and the other even result at a time

Such entangled pair of atoms can be produced, if the atoms are extremely cold and this has been done by the researchers in Hannover, in Germany. In that research, scientists cooled about 10,000 rubidium atoms very near to absolute zero point and found that the atoms form entangled pairs.

Dr. Carsten Klempt, physicist at the Institute of Quantum Optics at Leibniz Universität Hannover, said,

“In a series of measurements, we showed that these entangled atom pairs are indeed suited for high precision measurements beyond the shot noise limit. This process will enable future atomic clocks to benefit from entanglement, which Einstein called a spooky action.”


B. Lücke, M. Scherer, J. Kruse, L. Pezzé, F. Deuretzbacher, P. Hyllus, O. Topic, J. Peise, W. Ertmer, J. Arlt, L. Santos, A. Smerzi, C. Klempt, (2011). Twin Matter Waves for Interferometry Beyond the Classical Limit. Science, DOI: 10.1126/science.1208798


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