Quantum Physics Titans Win Breakthrough Prize

Quantum Physics Titans Win Breakthrough Prize

As billions of dollars pour into quantum computing and countries build communication networks secured by quantum encryption, the prominence of quantum information science has become increasingly hard to ignore.

This award is for four pioneers in quantum information science, math, and computer science. It is part of the Breakthrough Prize in Fundamental Physics.

” These four people really contributed heavily towards the emergence of quantum Information Theory,” says Nicolas Gisin (an experimental quantum physicist from the University of Geneva). “It’s nice that these prizes are closer to my heart .”

The Breakthrough Prizes were co-founded by Israeli-Russian billionaire and physicist Yuri Milner in 2012, and they have been lavishly supported by other moguls, including co-founders Mark Zuckerberg and Sergey Brin. Milner’s past financial ties with the Kremlin are similar to Alfred Nobel’s Nobel Prize-funding fortune from his invention of Dynamite. This is especially relevant in light of Russia’s ongoing invasion of Ukraine. Milner has stressed his independence and support for the Ukrainian refugees in previous interviews. A spokesperson pointed out to Scientific American that Milner relocated to the U.S. in 2014 and has not returned to Russia since.

However, recognition for quantum information science is not always easy or possible without such financial support. The field is a combination two theories: quantum mechanics which describes the counterintuitive behavior in the atomic and subatomic worlds and information theory which details the mathematical limits and physical limits of computation and communications. Its history is more complicated, with sporadic advancements that were often overlooked in 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. Wiesner, who was unable to publish many of his eloquent theoretical ideas and was drawn to religion, left academia last year to become a construction worker for Israel.

Before Wiesner left Columbia he passed some of his ideas on to another young researcher. Bennett recalls that Stephen Wiesner was one of his roommates and began telling him about his “quantum money”. “[It] struck me as 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 discussing Wiesner’s money, which they imagined might require the improbable task of trapping photons with mirrors to create a quantum banknote.

“Photons don’t have to stay, they’re meant for travel,” Brassard explains. “If they travel, what’s more natural than communicating?” The protocol Bennett and Brassard proposed, called BB84, would launch the field of quantum cryptography. Later detailed and popularized in Scientific American, BB84 allowed two parties to exchange messages with utmost secrecy. A third party could snoop on the exchanges and leave indelible evidence, such as damaging a quantum wax seal.

While Bennett and Brassard created quantum cryptography, a new idea was emerging: quantum computing. A now-famous meeting took place at M.I.T. 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. Deutsch was not able to attend the conference but he heard about it and was immediately hooked. He says, “I became more and more convinced about the links between computations and physics.”

Chatting later that year with Bennett, Deutsch experienced a crucial epiphany. The prevailing computational theory was based upon the wrong physics – the “classical” mechanics and relativistic approach of Albert Einstein instead of the deeper quantum reality. “So I thought I’d rewrite my theory of computation, basing that on quantum theory instead than classical theory,” Deutsch states matter-of-factly. It didn’t promise anything new. I just expected it to be more rigorous.” Soon, however, he realized he was describing a vastly different kind of computer. It achieved the same results using quantum mechanics principles.

Deutsch’s theory was a key link between quantum mechanics, information theory, and other theories. Umesh Vazirani is a computer scientist at University of California, Berkeley. “It made quantum mechanics available to me in my language of computing science,” he says. Later, with Australian mathematician Richard Josza, Deutsch proposed, as a proof of principle, the first algorithm that would be exponentially faster than classical algorithms–although it didn’t do anything practical.

But soon, more useful applications appeared. In 1991 Artur Ekert, then a graduate student at Oxford, proposed a new quantum cryptography protocol, E91. Many physicists were attracted to the technique’s simplicity and practicality, as well as the fact it was published in a leading journal of physics. It’s a beautiful idea. Gisin states that it is a bit surprising that Ekert has not been included in the “list” of recipients of this year’s Breakthrough Prize in fundamental physics.

Two years later, when Bennett, Brassard, Josza, computer science researcher Claude Crepeau, 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 flip, to another via entanglement, the quantum correlation that can link objects such as electrons. Despite popular science-fiction assertions, this technique does not allow for faster-than-light messaging–but it has dramatically expanded the possibilities of real-world quantum communications. “That’s the most mind-boggling idea,” says Chao-Yang Lu, a quantum physicist at the University of Science and Technology of China, who has helped implement the technique from space.

Words like “revolution” are often used to describe scientific progress, which is often slow and incremental. But in 1994 Shor quietly began one. He had attended talks by Bennett and Vazirani while working at AT&T Bell Laboratories. He says, “I started to think about what useful things it could do with a quantum computer.” “I thought it was a long shot. It was an interesting area. So I began to work on it. I didn’t tell anyone

Inspired by the success other quantum algorithms had with tasks that were periodic, or repeating, Shor developed an algorithm that could divide numbers into their prime factors (for example, 21=7 x 3) exponentially quicker than any classical algorithm. It was immediately apparent that prime factorization was the foundation of modern encryption. Quantum computers finally had a practical application that was truly revolutionary. Shor’s algorithm “just made it absolutely clear that you have to drop everything” to work on quantum computing, Vazirani says.

Although Shor had identified a strong use case for a quantum computing device, he still had to solve the difficult problem of how to make one–even though he had tried. These devices were also extremely vulnerable to errors due to the fragile quantum states they could exploit to outperform classical computing. Also, error correction strategies that were used for classical computers couldn’t be used in quantum computers. Undeterred, at a quantum computing conference in Turin, Italy, in 1995, Shor bet other researchers that a quantum computer would factor a 500-digit number before a classical computer did so. (Even with today’s classical supercomputers, factoring 500 digits would likely take billions of years.) Shor’s bet was not accepted by anyone, so some people asked for a third option. That the sun would go out first.

Quantum computers are plagued by two types of errors: phase errors and bit errors. These errors are similar to flipping a compass needle between north and south or east to west. Unfortunately, correcting phase errors can make them worse. Also, a more precise bearing north will result in a less accurate bearing west or east. But later in 1995 Shor figured out 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 factored with the algorithm is 21, so classical factoring remains in the lead–for now). It made quantum computing possible, even though it was not practical. Brassard says that this is when quantum computing became real.

All of this work led to new views of quantum mechanics and computing. For Deutsch, it inspired an even more fundamental theory of “constructors”–which, he says, describe “the set of all physical transformations.” Others remain agnostic about the likelihood of further deep insights emerging from the quantum realm. Shor states, “Quantum mechanics are really strange, and it’s not going to be easy to understand it.” Asked whether his work on quantum computing makes the nature of reality easier or harder to understand, he impishly says, “It certainly makes it more mysterious.”

What began as an eclectic intellectual pursuit or a hobby has grown to be a field that is far more than many of its pioneers could have imagined. It was never something we expected to become a reality. Brassard says it was just a lot fun to think about these crazy ideas. “At some point we realized we were serious, but people weren’t following us. It was frustrating. Now that it’s being recognized to such an extent is extremely gratifying.”

ABOUT THE AUTHOR(S)

    Daniel Garisto is a freelance science journalist covering advances i

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