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Quantum computing: To boldly go where Einstein feared to tread

To build a quantum computer — and to understand what it's good for — scientists will have to stretch their minds farther than Einstein could stretch his.

IQIM Caltech / YouTube

It was the scientific equivalent of a heavyweight title fight, but less conclusive. During the 1920s and ’30s, two of the century’s greatest physicists, Albert Einstein and Niels Bohr, locked brains in a series of debates. Bohr argued that physicists must learn to accept the weird behavior of subatomic particles: Their essential unpredictability even under completely controlled conditions, and a still stranger effect called entanglement, in which two particles, no matter how far apart, behave in ways that, while individually random, are too strongly correlated for the particles to be acting independently.

Einstein was deeply troubled by these phenomena, disparaging the former as "God playing dice" and the latter as "spooky action at a distance." He spent his remaining years searching unsuccessfully for a more naturalistic theory, where every effect would have a cause, and influences would act locally. Newton’s physics, Maxwell’s electromagnetism and Einstein's own theory of relativity share this common-sense property, which he deemed essential to any lawful and orderly explanation of nature.

Meanwhile, the rest of the physics community, including greats like Schrödinger, Heisenberg and Dirac, followed Bohr’s advice and accepted these disturbing phenomena, and the mathematics that explained them, as the new normal.

Some of the world’s most influential university laboratories, government agencies and technology companies are racing to design and build a "quantum computer.

Now, 90 years later, it’s pretty clear that the greatest scientific mind of the 20th century, flexible enough to bend space and time, wasn’t flexible enough. Quantum randomness and entanglement are real, confirmed by innumerable experiments, and explained in meticulous detail by the theory Einstein rejected. Moreover, quantum theory has played an essential role in technologies such as the laser and the transistor, which could not have been developed on the pre-quantum physics of Newton, Maxwell and Einstein.

But Einstein’s uneasiness lives on. Even the physicists who use quantum theory every day, and who all agree on how to use its mathematics to explain and predict the results of experiments, can’t agree on words to say what’s happening, or on how to fit quantum phenomena into some new and expanded version of common sense. Many concluded that this disconnect between mathematics and intuition was permanent, and that since it was fruitless to try to explain quantum phenomena in everyday language, physicists should just "shut up and calculate."

This worked pretty well for most of the 20th century, when quantum theory was regarded as a branch of physics, and physicists didn’t need to explain the theory to use it to design computer chips and cellphones. But toward the end of the 20th century, scientists gradually realized that quantum weirdness was not just a philosophical conundrum or a communications problem between scientists and laypeople, but implied the existence of powerful and previously unsuspected kinds of information processing, feats that could not be predicted or understood using pre-quantum notions.

Now, in the 21st century, this realization is propelling a race among some of the world’s most influential university laboratories, government agencies and technology companies, to design and build a "quantum computer," that is to say a device within which quantum effects are directly harnessed for information processing, including some feats unachievable by ordinary "classical" computers.

Aside from quantum computing's well known roles in encryption and code-breaking, mainly of interest to governments, a quantum version of cloud computing could give users the confidence, based on inviolable laws of physics, that their data remains safe from snooping and hacking, even if stored and processed God knows where by God knows whom. More broadly, by functioning the way nature does, quantum computers offer the hope of simulating (and therefore improving upon) natural processes in ways no classical computer could.

A quantum version of cloud computing could give users the confidence, based on inviolable laws of physics, that their data remains safe from snooping and hacking, even if stored and processed God knows where by God knows whom.

However, to properly explore this new field, scientists and technologists will need to understand quantum laws in a deeper and more intuitive way than most of them have until now. The educational system will have to adapt, training future scientists to be seasoned quantum cooks, instead of mere followers of recipes from the quantum cookbook.

One of the most promising efforts in this direction is Chris Cantwell's quantum chess, a game designed to show players, including ones too young to have taken a math or science course, how entanglement works, rather than attempting to tell them how it works. Here one can see a few friendly games played between Cantwell and chess expert Anna Rudolf, who knew no physics beforehand.

At a more advanced level, IBM is offering the "IBM Quantum Experience" website, through which scientists and amateurs all over the world can explore quantum computing, and even run simple problems on IBM's superconducting quantum computing hardware. Experiences like these will be necessary to develop the quantum intuition of the future, and to realize the promise of quantum computing.

When told of any scientific innovation, practical-minded people always want to know what it's good for — or, in modern parlance, whether it has a "killer app." The honest answer is that we don't know, but it must be explored to find out.

Quantum information science has brought the biggest change in our understanding of the nature of information and computation since these concepts were crystallized (alas, classically) in the mid-20th century, but only time will tell what it will eventually be used for.

Charles H. Bennett, a physicist, information theorist and IBM Fellow at IBM Research, is one of the founders of modern quantum information theory. Since joining IBM Research in 1972, he has worked on various aspects of the relation between physics and information processing, including the energy cost of mathematical operations, quantum cryptography and quantum teleportation. His work contributed many of the basic building blocks for quantum information processing, and continues to guide experimental work to build a universal quantum computer. Reach him @chdbennett.

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