Two-way communication of single quantum particles is possible.


Communication is a two-way street. Thanks to quantum mechanics, even if you have only one particle to transmit information, this proverb applies.

Scientists use a pair of new photons to report that two people can send information to another person at the same time using a single photon or photon. The feat relies on the quirks of quantum mechanics, which can effectively occupy two places at once.

Sending information through quantum particles is a very popular subject, thanks to unmeasured quantum communication (SN: 12/23/17, p. 27). The new study specifies distortions that have not been identified before this type of technology. “Sometimes you ignore a cool idea, and then it’s right in front of your nose,” said Philip walther, an experimental physicist at the university of Vienna.

Theoretical physicist at the university of Vienna, Flavio Del Santo and Austrian academy of sciences institute of quantum optics and quantum information BorivojeDaki level on February 9, “physical review letters” describes the theory behind this program. Walther, Del Santo, Daki and colleagues demonstrated the technique in a paper published on February 14 in

Imagine two people, Alice and Bob, at a distance. In standard classical physics, Alice and Bob both ask their own photons to send each other’s messages simultaneously, each sending a zero or one bit.

But if Alice and Bob have a in the overlapping position of the photons – at the same time near near Alice and Bob – they can operate the photons to encode 0 or 1, and then send it back to another. Each manipulated photon determines which one eventually receives the photon. If Alice and Bob put in the same bit – either 0 or both are 1 second – Alice receives the photon. If their bits don’t match, Bob gets it. Because Alice knows whether she sends 0 or 1, she immediately knows whether Bob is encoding 0 or 1, and vice versa.

To show that this communication is possible, Walther and colleagues send single photons by arranging mirrors and other optical devices. This setting gives the photon superposition and sends it to two stops representing Alice and Bob.

The researchers used 0 or 1 encoded photons on each stage by changing the phase of the light’s electromagnetic waves, where the waves and peaks fell. Then, at each station, the photons between Alice and Bob – still sitting idle – were taken to the opposite station. Along the way, the photon interacts with itself, interfering with the strength or offset of a ripple of water. This interference determines whether the final photon is detected at Alice’s station or Bob’s.

“It’s a very good idea,” said Giulio Chiribella, a physicist at Oxford University who was not involved in the study. “This is another way quantum mechanics allows us to relax our vigilance.”


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