Quantum computers are still a dream, but the era of quantum communication has already arrived. A new experiment conducted in Paris, showed that the quantum message is superior to the classical methods of information transfer.
“We were the first to demonstrate a quantum advantage in transmitting information, which is necessary for the two parties to complete the task,” says Eleni Diamanti, an electrical engineer from the University of Sorbonne and co-author of the study.
It is expected that quantum machines — which use quantum properties of matter to encode information — will revolutionize computing. But progress in this area has been extremely slow. While engineers are working to create an elementary quantum computers, theorists are faced with a more fundamental obstacle: they could not prove that classical computers will never be able to perform tasks that quantum computers. Last summer, for example, the guy from Texas has proven that a problem that has long been considered to be solved only on a quantum computer, can be resolved quickly and to the classic.
Welcome to the quantum age
However, in the field of communication (not computation) advantages of the quantum approach can be confirmed. More than ten years ago, scientists proved that, at least in theory, quantum communication exceeds the classical methods of sending messages to certain tasks.
“People mainly engaged in computational tasks. One of the big pluses is that in the case of communication tasks advantages provable”.
In 2004, Iordanis Kerasidis, co-author Diamanti, and two scientists presented a scenario in which one person had to send information to another that the second person could answer a specific question. Researchers have shown that a quantum circuit can perform the task, transferring exponentially less information than a classical system. But quantum scheme, which they introduced, was purely theoretical and far beyond the technology of the time.
“We were able to confirm this quantum advantage, but to realize the quantum Protocol was extremely difficult,” says Ceramides.
The new work is a modified version of the script provided by Ceredigion and his colleagues. As usual, please refer to the two entities, Alice and Bob. Alice has a set of numbered balls. Each ball is randomly colored red or blue. Bob wants to know whether a specific pair of balls, randomly selected, the same color or different. Alice wants to send Bob the smallest amount of information possible, while ensuring that Bob can answer your question.
This problem is called “pattern matching problem”. It is essential for cryptography, and digital currency where users often want to share information without disclosing everything they know. It perfectly demonstrates the advantages of quantum communication.
You can’t just say I want to send you a movie or something the size of a Gigabyte and encode it into a quantum state, expecting to find quantum advantage, says Thomas Vidic, a computer scientist from the California Institute of technology. “We need to consider more subtle tasks.”
For the classical solution of the problem of Association, Alice must send to Bob the amount of information is proportional to the square root of the number of balls. But the unusual nature of quantum information make possible a more effective solution.
In the laboratory system used in the new work, Alice and Bob are communicating with help of laser pulses. Each pulse represents one ball. The pulses pass through a beam splitter, which sends half of each pulse to Alice and Bob. When a pulse reaches Alice, she can shift the phase of the laser pulse to encode information about each ball, depending on its color, red or blue.
Meanwhile, Bob encodes information about pairs of balls that he was interested in his half of the laser pulses. Then the pulses converge at another beam splitter where the interfere among themselves. The pattern of interference created by the pulses, reflect differences in how the shifted phase of each pulse. Bob can read the pattern of the interference at the near detector of photons.
Until Bob “read” a laser message from Alice’s quantum message Alice can answer any question about any pair. But the process of reading a quantum message destroys it, and Bob receives the information of only one pair of balls.
This property of quantum information is that it can be read in different ways, but ultimately it will be read only one — greatly reduces the amount of information that can be passed to solve the matching sample. If Alice needs to send Bob 100 classic bits that he was able to answer your question, it can perform the same task with about 10 qubits, or quantum bits.
That is the proof of the principle you need to build a real quantum networks, says Graham Smith, a physicist from JILA in boulder, Colorado.
A new experiment — to-one triumph over the classical methods. The researchers started the experiment knowing exactly how much information you need to pass the classical way to solve the problem. Then they demonstrated that quantum tools help to solve it more compact.
This result also provides an alternative route to achieve a long-standing goal in computer science: proof that quantum computers are superior to classical.
When do you think we will have desktop quantum computers?