Scientists from Spain and South Africa transmit an image through the quantum network

magazine Nature Communications Recently published research conducted by scientists at the University of the Witwatersrand (Wits, South Africa) and Institute of Photonic Sciences (ICFO), which indicates Transmitting a printed image in a beam of light across a network without actually transmitting the image. This is an important step towards creating a quantum network to transmit information written in a high-dimensional alphabet.

the Long-distance quantum communications It is an essential part of information security and has been demonstrated using two-dimensional states (qubits) over very long distances between satellites. This may seem sufficient when compared to its classical counterpart, i.e. sending bits that can be encoded into 1 (signal) and 0 (unsignal), one after the other. However, Quantum optics It allows us to augment the alphabet and securely describe more complex systems in a single presentation, such as a fingerprint or a unique face.

Star Trek technology.

“Traditionally, two entities communicate with each other by physically sending information from one to the other, even in the quantum world,” says the professor. Andrew Forbes“, lead researcher at Wits, who adds: “It is now possible Information is transferred instantaneously so that it is never physically transmitted Through communication: technology Star Trek “It will come true.”

So far, teleportation has only been demonstrated between two parties using low-dimensional alphabets, requiring multiple entangled photons to send complex images.

In this study, the team performed the first experimental demonstration of quantum teleportation for high-dimensional states using only two entangled photons as a quantum resource, resulting in information appearing to pass from sender to receiver. To advance use the team Nonlinear optical detector This avoids the need for additional photons, but works with any “pattern” that needs to be transmitted.

Thanks to their technology, scientists say they can Send information written in a 15-dimensional alphabetwith a scheme scalable to higher dimensions, paving the way for quantum network communications with greater information capacity.

A new experience with Alice and Bob

In their experiment, the researchers came up with an elegant method for safe transportation Spatial information The high dimension between two parts, which is popular with us Alice and Bob (two artificial intelligences), using a scheme inspired by teleportation.

Unlike previous experiments that successfully transferred 3D states (using path entanglement), which unfortunately required the help of additional entangled photons, here the team used three entangled photons and two entangled photons, which form Quantum channel.

First, they encrypted the information to be transmitted instantly within a file “printed light source” An alphabet containing 15 elements. In parallel, they created a pair of entangled photons in these 15 dimensions. Of the pair of photons, the second entangled photon passed from Bob to Alice, and the interaction with the light source modeled on Alice was measured using a nonlinear spatial detector, through what is known as Bell State Measurement (BSM).

The effect of this measurement was to mix the states of the second photon and the light source in a second nonlinear crystal and perform a process Specific spatial projection On the single photon resulting from this measurement.

Now, thanks to the fact that the first and second photons were initially entangled, i.e. their combined states were highly correlated, The result of the BSM led to the transfer of encoded information From the coherent light source to the first photon that remained in the bob and was never in contact with the source.

Applications in the banking field

The potential of this new quantum transfer protocol is illustrated by the authors in the figure. Imagine a customer who wants to send confidential information to a bank, perhaps a fingerprint. In traditional quantum communications, information must be physically sent from the customer to the bank, with there always being a risk of it being intercepted (even if it is secure).

In the proposed quantum transmission scheme, the bank sends a single photon (one of the entangled pair) without information to the client, which in turn covers the photon on a nonlinear detector with the information to be sent.

as a result of, The information appears at the bank exactly as if it had been transferred there. The information is never actually sent between the two parties, so trying to intercept the signal is meaningless, while the quantum link connecting the two parties is created through the exchange of entangled quantum photons.

“This protocol has all the features of teleportation, except for one essential element: it requires the use of a file Intense laser beam So the nonlinear detector is effective, so the sender can know what is going to be sent, but he doesn't need to know it,” Forbes explains.

“In this sense, it is not strictly a matter of teleportation, but it may be in the future if the nonlinear detector can be made more efficient.” And even as it is now, It opens a new path for connecting quantum networksMarking the beginning of nonlinear quantum optics as a resource.

“We hope that these results proving the feasibility of the process will be motivating New developments in nonlinear optics“The frontier pushes us towards full quantitative implementation,” says Adam Valles of ICFO (Barcelona), one of the project leaders who worked on the experiment during a postdoctoral fellowship at Wits.

“We have to be careful, because this formation cannot be prevented,” he warns The deceptive sender keeps better copies of the information to be transferred, which means we could end up with multiple clones of Mr. Spock in a world Star Trek.

“In practice, the configuration we currently offer They can now be used to create a secure high-dimensional channel The researcher explained: “For quantum communications between two parties, as long as the protocol does not need to be fed with individual photons, as is the case with quantum repeaters.”

Doctoral research

“Performing such experiments using currently available technology has been an interesting adventure, and we have it to thank Berenice Sifton of Wit For his determination and extraordinary skills in taming such a massive experiment. This is the A real experimental effort Valles stressed that she should be praised.

Forbes echoes this sentiment: “This was a heroic experience and Dr. Sifton should be recognized She was the one who made the system work. And he conducted the main experiments.”

now, The team plans to continue working in this direction The next step will focus on quantum transmission over the fiber-optic network.