Four Pioneers in Quantum Information Receive 2023 Breakthrough Awards

On September 22, 2022, the Breakthrough Prize for 2023 was announced. Four pioneers in the field of quantum information, Charles H. Bennett, Gilles Brassard, David Deutsch, and Peter Shor, have been awarded the Breakthrough Prize in Fundamental Physics for their "fundamental work in quantum information. The award was given to four pioneers in the field of quantum information, Charles H. Bennett, Gilles Brassard, David Deutsch, and Peter Shor, for "fundamental work in quantum information.

The Breakthrough Prize, known as the "Oscars of Science," was founded in 2012 by Yuri Milner, a prominent Russian investor, along with entrepreneurs such as Facebook founder Mark Zuckerberg and Google founder Sergey Brin, and is awarded in the fields of life sciences, fundamental physics and mathematics for $3 million each.

In the field of fundamental physics, the prize was awarded to four pioneers in the field of quantum information.

Charles H. Bennett and Gilles Brassard created the BB84 protocol, which pioneered quantum cryptography. Together with collaborators, they discovered quantum invisible transitions.

David Deutsch laid the foundations of quantum computing. He defined the quantum Turing machine - the universal quantum computer - and proved that it could simulate with arbitrary accuracy any physical system that obeyed the laws of quantum mechanics. He also designed the first quantum algorithm that surpassed the best equivalent classical algorithm.

Peter Shor invented the first practical quantum algorithm, Shor's algorithm is able to find the prime factors of large numbers quickly, with exponential speedup compared to any classical algorithm. He also designed error correction techniques for quantum computers.

01The early years of a quantum pioneer

In 1968, Stephen Wiesner, then a graduate student at Columbia University, developed a new method of encoding information using polarized photons. wiesner proposed that the inherent fragility of the quantum state could be used to create counterfeit-proof quantum currency. At the time, he wrote a paper titled "Conjugate Coding," but the idea was so far ahead of its time that it was rejected time and time again by journals. This led Wiesner to quit academia and emigrate to Israel to become a construction worker.

Before Wiesner left Columbia, he passed on some of his ideas to another young researcher, Charles Bennett. Bennett recalls, "One of my roommate's boyfriends was Wiesner, and he started telling me about his 'quantum money,' which I thought was interesting, but it wasn't like the beginning of a whole new field."

In the late 1970s, Bennett met Brassard and the two began discussing Wiesner's quantum money, which they thought might require the unlikely task of capturing photons in a mirror to make quantum banknotes.

Brassard explains the thought process, "Photons shouldn't stay - they should travel. If they travel, what could be more natural than communication?" The protocol proposed by Bennett and Brassard became known as BB84, and it pioneered the field of quantum cryptography. Later described and promoted in detail in Scientific American, BB84 allows two parties to exchange information in extreme secrecy. If a third party snooped, they would be left with indelible evidence of interference - just like breaking a quantum wax seal.

While Bennett and Brassard were developing quantum ciphers, another radical idea began to surface: quantum computing.

In May 1981, a prestigious conference was held at MIT's Endicott Building. Nobel Prize-winning physicist Richard Feynman proposed that computers using quantum principles could solve problems that computers bound by the laws of classical physics could not. Although he did not attend the conference, Deutsch was intrigued by the idea when he heard about it. "I grew more and more convinced of the connection between computing and physics," he says.

Later that year, while talking with Bennett, Deutsch experienced an important epiphany: the then-popular theory of computation was based on Isaac Newton's "classical" mechanics and Albert Einstein's relativistic approach, rather than the deeper quantum reality. "So I thought I'd rewrite the theory of computation and base it on quantum theory rather than classical theory," Deutsch says matter-of-factly. "I don't expect it to lead to anything fundamentally new. I just expected it to be more rigorous." Soon, however, he realized that he was describing a completely different kind of computer. Even if it got the same results, it was derived from the principles of quantum mechanics.

Deutsch's new theory provides an important link between quantum mechanics and information theory. "It (the theory) allowed me to understand quantum mechanics in my computer science language," explains Umesh Vazirani, a computer scientist at the University of California, Berkeley. Later, Deutsch worked with Australian mathematician Richard Josza to come up with the first algorithm that was much faster than the classical algorithm, even though it didn't do anything practical - it was a proof of principle.

But soon more useful applications emerged. in 1991, Artur Ekert, then a graduate student at Oxford University, proposed a new quantum cryptographic protocol, E91. the technique attracted the attention of many physicists for its elegance and practicality, and for the fact that it was published in a leading physics journal. "It's a great idea. Surprisingly, Ekert was not selected as a winner of this year's Breakthrough Prize in Fundamental Physics," said Nicolas Gisin, an experimental quantum physicist at the University of Geneva.

Two years later, Bennett, Brassard, Josza, computer science researcher Claude Crépeau and physicists Asher Peres and William Wootters proposed quantum invisible transfer, which again attracted the attention of physicists. This new technique would allow one party to pass information (such as the result of a coin flip) to another party through entanglement. Entanglement is a quantum association that can connect objects such as electrons, and this association greatly extends the possibilities of real-world quantum communication. "It's the most incredible idea," said Lu Chaoyang, a quantum physicist at the University of Science and Technology of China who has been involved in implementing the technology in space.

Words like "revolution" are often used to describe scientific progress, which is usually slow and incremental. But Peter Shor quietly began a "revolutionary" study in 1994. While working at AT&T's Bell Labs, he absorbed the conversations of Vazirani and Bennett. "I started thinking about what quantum computers could do that would be useful," he says. "I thought there was little hope. But it's a very interesting field. So I started looking into it. I really didn't tell anyone about it."

Inspired by the success of other quantum algorithms for periodic or repetitive tasks, Shor developed an algorithm that can decompose numbers into prime factors (e.g., 21 = 7 x 3) at an exponential rate faster than any classical algorithm. The implication is obvious: prime factorization is the backbone of modern encryption. Quantum computers finally have a real game-changing practical application.

Vazirani says that Shor's algorithm "makes it very clear that you have to drop everything" to engage in quantum computing.

Although Shor has discovered a powerful use case for quantum computers, he has yet to solve the more difficult problem of how to build one - even in theory. The fragile quantum states that such devices can be used to go beyond classical computing also make them extremely error-prone. Moreover, the error-correction strategies of classical computers cannot be used in quantum computers.

But Shor was not deterred, and in 1995, at a conference on quantum computing in Turin, Italy, he and other researchers bet that quantum computers would break down 500-bit numbers before classical computers. This seemed like nonsense to others, because even using today's classical supercomputers, breaking down 500 digits could take billions of years. No one accepted Shor's bet, and some gave a third option: the sun would burn out first.

Two types of errors plague quantum computers: bit-flips and phase-flips. These errors are similar to flipping a compass needle from north to south or from east to west, respectively. Unfortunately, correcting bit-flip errors makes phase-flip errors worse, and vice versa. In other words, a more accurate bearing north would result in a less accurate bearing east or west. But later in 1995, Shor discovered how to combine bit correction and phase correction in a series of operations that were like solving a Rubik's cube without changing the completed side. Shor's algorithm remained ineffective until quantum computers became more powerful (the algorithm's highest factorization number is 21, so classical factorization is still in the lead for now). But even if it's not practical, it still makes quantum computing possible, says Brassard: "It's all becoming a reality." .

All this work brought new perspectives on quantum mechanics and computation.

For Deutsch, it inspired a more fundamental "constructor" theory, which he says is a description of "the set of all physical transformations. Others remain unaware of the possibility of further profound insights in the quantum realm. "Quantum mechanics is really weird, and I don't think there's any easy way to understand it," Shor said. Asked if his work on quantum computing makes the nature of reality easier or harder to understand, he says mischievously, "It certainly makes it more mysterious."

What began as a pastime or an eclectic academic pursuit, quantum information science has now gone far beyond many of the wildest imaginings of the field's pioneers.

We never thought it would become practical," says Brassard. It's so much fun to think about these crazy ideas. In a way, we think we're serious, but people aren't paying attention to us. It was frustrating. It's very gratifying that it's now recognized to this extent."

Reference links：

[1]https://breakthroughprize.org/News/73

[2]https://www.scientificamerican.com/article/quantum-physics-titans-win-breakthrough-prize/