Two entangled light beams are produced by a new light source that researchers have created.

 

via José Tadeu Arantes

the study's optical parametric oscillator (OPO). Alvaro Montaa Guerrero is to blame.

Quantum entanglement, which happens when two or more systems are produced or interact in such a way that the quantum states of some cannot be characterised independently of the quantum states of the others, is being studied by scientists more and more. Even though the systems are far apart, they are still correlated. Research is encouraged by the substantial potential for applications in communications, cryptography, and quantum computing. The problem is that the systems very instantly detangle when they interact with their environment.

Brazilian researchers from the Laboratory for Coherent Manipulation of Atoms and Light (LMCAL) at the Physics Institute of the University of So Paulo (IF-USP) succeeded in creating a light source that generated two entangled light beams. Physical Review Letters covers the results of their research.

"An optical parametric oscillator, or OPO, which generally consists of a non-linear optical response crystal sandwiched between two mirrors to form an optical cavity, was the source of this light. Two light beams with quantum correlations are produced by the crystal-mirror dynamics when a strong green laser beam strikes the apparatus "Hans Marin Florez, a physicist and the article's final author, claimed this.

The issue is that because the light emitted by crystal-based OPOs has a different wavelength than the systems in question, such as cold atoms, ions, or chips, it cannot interact with other systems of relevance in the context of quantum information. "In earlier work, our team demonstrated that atoms themselves may be employed as a medium rather than a crystal. Thus, using rubidium atoms as the basis, we created the first OPO with two beams that were strongly quantum correlated and acquired a source that may interact with other systems that can operate as quantum memory, such as cold atoms "Florez said.

This did not, however, prove that the beams were intertwined. In order to show quantum correlations, the beams' phases, which have to do with light wave synchronisation, were also necessary. In the latest study published in Physical Review Letters, we precisely accomplished it, he stated.

"We carried out the same experiment again while including fresh detection procedures that allowed us to quantify the quantum correlations in the amplitudes and phases of the produced fields. We were able to demonstrate their interconnection as a result. Additionally, we were able to see that the entanglement structure was richer than would generally be defined thanks to the detection method. What we had truly created was a system made up of four entangled spectral bands, not just two neighbouring spectral bands."

In this instance, the wave amplitudes and phases were mixed up. This is crucial to many protocols used to handle and transmit information that has been quantum-coded. In addition to these potential uses, this form of light source may also be employed in metrology. According to Florez, quantum correlations of intensity lead to a significant decrease in intensity fluctuations, which might improve the sensitivity of optical sensors. "Just try to hear someone across the room at a party where everyone is talking at once. If everyone stops talking and the noise level drops enough, you can hear what someone is saying from a fair distance away."

One of the potential uses, he continued, is boosting the sensitivity of atomic magnetometers used to gauge the alpha waves produced by the human brain.

An additional benefit of rubidium OPOs over crystal OPOs is also mentioned in the paper. The use of an atomic medium, in which the two beams are produced more efficiently than with crystals, avoids the need for mirrors to imprison the light for such a long time, according to Florez. "Crystal OPOs have to have mirrors that keep the light inside the cavity for longer, so that the interaction produces quantum correlated beams," Florez said.

Other teams had attempted to create OPOs using atoms before his team did, but they had been unable to show quantum correlations in the light beams they generated. The results of the new experiment demonstrated that there was no systemic restriction that would have prevented this. "We found that seeing quantum correlations depends critically on the atoms' temperature. Evidently, the researchers were unable to detect links in the other investigations since they were conducted at greater temperatures, "added he.