Quantum Entanglement Characterization Could Lead to Ultra-Sensitive Optical Gradiometers

Experimental physicist Rainer Blatt and his team have been successful in characterizing the quantum entanglement of two spatially separated atoms by monitoring their light emission. This key demonstration could result in the development of extremely sensitive optical gradiometers for the precise measurement of the earth's magnetic field or gravitational field.

Physicists compared the photon interference produced by entangled and non-entangled barium atoms. (Image credit: IQOQI Innsbruck/Harald Ritsch)

The era of quantum technology has long been foretold. Years of research into the quantum realm have resulted in the development of approaches that make it possible at present to manipulate quantum properties, especially for technical applications. Innsbruck quantum computer pioneer Rainer Blatt and his team managed to control individual atoms very precisely in experiments using ion traps.

The deliberate entanglement of these quantum particles not only paves the way to the possibility of creating a quantum computer but also forms the basis for the measurement of physical properties with formerly unknown precision. For the first time, the physicists have successfully shown fully-controlled free-space quantum interference of single photons radiated by two effectively-separated entangled atoms.

Sensitive Measurements

"Today, we can very precisely control the position and entanglement of particles and generate single photons as needed," explains Gabriel Araneda from Rainer Blatt's team from the Department of Experimental Physics at the University of Innsbruck. "Together, this allows us to investigate the effects of entanglement in the collective atom-light interaction."

The physicists at the University of Innsbruck compared the photon interference formed by entangled and non-entangled barium atoms. The measurements revealed that these are qualitatively not the same. Actually, the measured difference of the interference fringes directly relates to the amount of entanglement in the atoms.

"In this way, we can characterize the entanglement fully optically," Gabriel Araneda stresses the importance of the experiment.

The researchers were also able to show that the interference signal is very sensitive to environmental influences at the location of the atoms. "We take advantage of this sensitivity and use the observed interference signal to measure magnetic field gradients," says Araneda.

This method may result in the development of ultra-sensitive optical gradiometers. Since the measured effect does not depend on the proximity of the atoms, these measurements could permit to exactly compare field strengths at separated locations, such as that of the earth's magnetic or gravitational fields.

The research was reported in the journal Physical Review Letters and was funded by the Austrian Science Fund FWF, the European Union and the Federation of Austrian Industries Tyrol, among others.

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