The Titans of Quantum Physics win the revolutionary prize

As billions of dollars pour into quantum computing and countries build communications networks protected by quantum cryptography, the importance of quantum information science has become increasingly difficult to ignore.

This year’s Breakthrough Prize in Fundamental Physics honors four pioneers who have combined mathematics, computer science and physics to do “fundamental work in the field of quantum information”. The award is shared between Charles Bennett of IBM, Gilles Brassard of the University of Montreal, David Deutsch of the University of Oxford and Peter Shor of the Massachusetts Institute of Technology.

“These four people really contributed greatly to the emergence of quantum information theory,” says Nicolas Gisin, an experimental quantum physicist at the University of Geneva. “It’s nice to see these awards come close to my heart.”

The Breakthrough Prizes was co-founded by Israeli-Russian billionaire and physicist Yuri Milner in 2012 and was generously supported by other tycoons, including co-founders Mark Zuckerberg and Sergey Brin. Similar to Alfred Nobel, whose Nobel Prize funding fortune stemmed from his invention of dynamite, Milner’s past financial ties to the Kremlin have drawn attention, especially in light of the ongoing invasion of Ukraine by of Russia. In previous interviews, Milner highlighted his independence and donations to Ukrainian refugees. A spokesperson pointed out American scientist that Milner moved to the United States in 2014 and hasn’t returned to Russia since.

But recognition for quantum information science hasn’t always been easy, or with such financial backing. In general, the field is a combination of two theories: quantum mechanics, which describes the counterintuitive behavior of the atomic and subatomic world, and information theory, which details the mathematical and physical limits of computation and communication. His story is a more disordered story, with sporadic advances that have often been overlooked by conventional scientific journals.

in 1968, Stephen Wiesner, then a graduate student at Columbia University, developed a new way of encoding information with polarized photons. Among other things, Wiesner proposed that the inherently fragile nature of quantum states could be used to create counterfeit-resistant quantum money. Unable to publish many of his heady theoretical ideas and drawn to religion, Wiesner, who died last year, largely left academia to become a construction worker in Israel.

Before Wiesner left Columbia, he passed on some of his ideas to another young researcher. “One of my roommates’ boyfriends was Stephen Wiesner, who started talking to me about his’ quantum money ‘,” Bennett recalls. “[It] I thought it was interesting, but it didn’t seem like the beginning of a whole new field. “In the late 1970s Bennett met Brassard and the two began to discuss Wiesner’s money, which they imagined might require the unlikely task of trapping photons with the mirrors to create a quantum banknote.

“Photons aren’t meant to stay, they’re meant to travel,” says Brassard, explaining the thought process. “If they travel, what’s more natural than communicating?” The protocol proposed by Bennett and Brassard, called BB84, would launch the field of quantum cryptography. Later detailed and popularized American scientist, BB84 allowed two parties to exchange messages with the utmost secrecy. If a third party were to snoop, it would leave indelible evidence of their interference, such as damaging a quantum wax seal.

As Bennett and Brassard developed quantum cryptography, another radical idea began to emerge: quantum computing. In a now famous meeting at the MIT Endicott House in Dedham, Mass., In May 1981, physicist Richard Feynman proposed that a computer using quantum principles could solve problems impossible for a computer bound by the laws of classical physics. Even though he didn’t attend the conference, Deutsch heard about the idea and was fascinated by it. “I gradually became more and more convinced of the links between calculus and physics,” he says.

Chatting with Bennett in the same year, Deutsch experienced a crucial epiphany: then the prevailing computational theory was based on the wrong physics: Isaac Newton’s “classical” mechanics and Albert Einstein’s relativistic approach rather than on deeper quantum reality. “So I thought of rewriting computation theory, basing it on quantum theory instead of basing it on classical theory,” says Deutsch concretely. “I didn’t expect anything fundamentally new to come out of it. I just expected it to be more rigorous. ”He soon realized, however, that he was describing a very different type of computer. Even though he got the same results, he came up with the principles of quantum mechanics.

Deutsch’s new theory provided a crucial link between quantum mechanics and information theory. “It made quantum mechanics accessible to me in my computer language,” says Umesh Vazirani, a computer scientist at the University of California, Berkeley. Later, with the Australian mathematician Richard Josza, Deutsch proposed, as a proof of principle, the first algorithm that would be exponentially faster than classical algorithms, although it did nothing practical.

But soon more useful applications emerged. In 1991 Artur Ekert, then an Oxford graduate student, proposed a new quantum encryption protocol, E91. The technique attracted the attention of many physicists for its elegance and practicality, as well as for the fact that it was published in one of the leading physics journals. “It’s a great idea. It’s a little surprising that Ekert isn’t on the list of winners of this year’s Breakthrough Prize for Fundamental Physics, says Gisin.

Two years later, when Bennett, Brassard, Josza, computer science researcher Claude Crépeau, and physicists Asher Peres and William Wootters proposed quantum teleportation, physicists were paying attention. The new technique would give one party the ability to transmit information, such as the result of a coin toss, to another through entanglement, quantum correlation that can connect objects such as electrons. Despite popular science fiction claims, this technique doesn’t allow for faster-than-light messages, but it has greatly expanded the possibilities of quantum communications in the real world. “This is the most stunning idea,” says Chao-Yang Lu, a quantum physicist at the University of Science and Technology of China who helped implement the technique from space.

Words like “revolution” are overused to describe the progress of science, which is usually strenuous and incremental. But in 1994 Shor quietly started one. While working at AT&T Bell Laboratories, he had absorbed the speeches of Vazirani and Bennett. “I started thinking about what useful things you could do with a quantum computer,” he says. “I thought it was a long shot. But it was a very interesting area. So I started working on it. I haven’t told anyone. “

Inspired by the success other quantum algorithms have had with periodic or repetitive tasks, Shor has developed an algorithm capable of dividing numbers into their prime factors (e.g., 21 = 7 x 3) exponentially faster than any classical algorithm. The implications were immediately obvious: primary factorization was the backbone of modern cryptography. Ultimately, quantum computers had a truly revolutionary practical application. Shor’s algorithm “just made it clear that you have to drop everything” to work on quantum computing, says Vazirani.

Although Shor had found a powerful use case for a quantum computer, he hadn’t solved the more difficult problem of how to build one, not even in theory. The fragile quantum states that such devices could exploit to overcome classical computing have also made them extremely vulnerable to errors. Furthermore, the error correction strategies for classical computers could not be used in quantum computers. Undaunted, at a conference on quantum computing in Turin, Italy in 1995, Shor wagered with other researchers that a quantum computer would calculate a 500-digit number before a classical computer did. (Even with today’s classic supercomputers, calculating 500 digits would probably take billions of years.) Nobody took Shor’s bet, and some asked for a third option: that the sun would go out first.

Two types of errors plague quantum computers: bit errors and phase errors. These errors are similar to flipping a compass needle from north to south or east to west, respectively. Unfortunately, bit error correction makes phase errors worse and vice versa. In other words, a more accurate northward bearing results in a less accurate east or west bearing. But later, in 1995, Shor discovered how to combine bit correction and phase correction, a chain of operations not unlike solving a Rubik’s cube without altering a completed side. Shor’s algorithm remains ineffective until quantum computers become more powerful (the highest number taken into account with the algorithm is 21, so classical factorization remains in the lead, for now). But he still made quantum computing possible, if not practical. “That was when the whole thing became real,” says Brassard.

All this work has led to new insights into quantum mechanics and computer science. For Deutsch, he inspired an even more fundamental theory of “builders” – which, he says, describe “the set of all physical transformations”. Others remain agnostic about the likelihood of further insights emerging from the quantum realm. “Quantum mechanics is really weird and I don’t think there will ever be an easy way to understand it,” says Shor. Asked if his work on quantum computing makes the nature of reality easier or harder to understand, he mischievously says, “It sure makes it more mysterious.”

What began as a pastime or an eclectic intellectual pursuit has now grown far beyond many of the wildest imaginations of the pioneers of the field. “We never thought it would ever become practical. It was just a lot of fun thinking about these crazy ideas, “says Brassard.” At one point we decided to get serious, but people didn’t follow us. It was frustrating. Now that it’s recognized to such an extent it’s extremely rewarding. “

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