According to media reports, quantum computers are still a dream, but the era of quantum communication has arrived. An experiment recently conducted in Paris confirmed for the first time the superiority of quantum communication compared with traditional information transmission methods.
“We demonstrated for the first time the advantages of quantum communication in disseminating information and helping both parties perform their tasks,” said Eleni Diamanti, an electronics engineer at the Sorbonne University in Paris. She is one of the co-authors of this research report. The scientists involved in the study also included computer scientists from the University of Paris 7 Lordanis Kerenidis and Niraj Kumar.
Quantum machines are machines that use the quantum properties of matter to encode information. It is widely believed that such machines will revolutionize computers. But the progress has been very slow. Engineers have been working hard to build basic quantum computers, while at the same time theoretical computer scientists have encountered a more fundamental obstacle: they cannot prove that classical computers can never complete the task of quantum computers. For example, just this summer, a teenager in Texas, USA, proved that a problem that has long been considered to be solved only by quantum computers can be solved quickly with a classic computer.
But in the field of communication, the advantage of the quantum approach is the fact that it is nailed. Computer scientists have proved more than a decade ago that, at least in theory, quantum communication has obvious advantages in sending information for specific tasks.
"Most people only focus on computing tasks. But one of the great advantages of studying communication tasks is that the advantages of quantum pathways in this area can be proven," said Kerry Dinis.
In 2004, Kerry Dinis and two other computer scientists envisioned a scenario where someone needs to send a message to another person so that the latter can answer a particular question. Researchers have shown that using quantum devices can greatly reduce the amount of information that needs to be transferred while completing tasks. But the quantum devices they envisioned at that time were purely theoretical, far beyond the state of the art.
"We could prove the advantages of quantum communication at the time, but it is difficult to apply it," said Karenides.
The new study has made some changes to the scenarios envisioned by Kerry Dinis and others. Two people are involved in the new scene, named A and B. A has a set of small balls with numbers, each of which is randomly painted red or blue. B wants to know if the randomly selected pair of balls are the same color or different. A wants to send B with as little information as possible to ensure that B can answer the question.
The problem, called the "sampling matching problem", is important for both cryptography and digital currency, because users often want to avoid revealing other information while exchanging information. And this problem is also very suitable to show the advantages of quantum communication.
"You can't say 'I want to send you a 1GB movie, now I'm coding it into a quantum state' and then expect to discover the quantum advantage," said Thomas Widick, a computer scientist at the California Institute of Technology. "You To verify with a more subtle task."
If the above problem is solved by the classical method, the amount of information that A needs to send to B needs to be proportional to the square root of the number of balls. But the singular nature of quantum information provides us with a more efficient solution.
In the laboratory setup used in this new study, A and B communicated via laser pulses. Each pulse represents a small ball. The pulse needs to pass through a splitter, splitting one pulse into two, half to A and half to B. When the pulse passes around A, A can change the phase of the laser pulse and encode the color information of each ball into it.
At the same time, B will put the information of the pair of balls he wants to know into his half of the laser pulse. These two halves of the pulse will then intersect at the other splitter, creating interference. The interference pattern of the two sets of pulses can reflect how the phase of each pulse has been adjusted. Next, B can read the interference fringes from the nearby photon detector. Until the moment B reads "A" laser information, A's quantum information can answer any questions related to any pair of small balls. But just as B read the information, he destroyed the quantum state and could only read information about a pair of small balls.
This is the characteristic of quantum information, which can have a variety of potential ways of being read, but can only be read in one way. This feature can significantly reduce the amount of information that needs to be passed to resolve sample matching problems. For example, to ensure that B can answer the question, A may need to send 100 classic bits of information to B, but with quantum methods, just send 10 qubits to achieve the same goal.
"To create a true quantum network, we need to do this proof of concept," said Graeme Smith, a quantum technology expert at the American Institute of Experimental Astrophysics.
This new experiment is clearly superior to the classical proof method. When the researchers conducted the experiment, it was clear how much information was needed to solve the problem in a classic way. Then they proved in an irrefutable way that solving the problem with the quantum approach is clearly better than the traditional approach. "We are very pleased to see in this paper that the researchers have spent a lot of time, first to ensure that the experiments they have done are difficult to complete with classical methods, and then use quantum methods to overcome this problem."
The computer science community has a long-lasting goal: to prove that quantum computers are indeed superior to classical computers. The results of this study may provide a new way to achieve this goal. This quantum "superiority" may be difficult to prove in the field of pure computing, but in addition to computing, there are many important issues worth solving.
"If we combine the computational and communication tasks that we can do with quantum methods, we can more easily prove the advantages of quantum." Kerry Dinis said.
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