October 23, 2019 5:15 pm
For the first time, a machine that runs on the mind-boggling physics of quantum mechanics has reportedly solved a problem that would stump the world’s top supercomputers – a breakthrough known as “quantum supremacy.”
If validated, the report by Google’s AI Quantum team constitutes a major leap for quantum computing, a technology that relies on the bizarre behavior of tiny particles to encode huge amounts of information. According to a paper published Wednesday in the journal Nature, Google’s Sycamore processor performed in less than three and a half minutes a calculation that would take the most powerful classical computer on the planet 10,000 years to complete.
The achievement has been compared to the Wright brothers’ 12-second first flight at Kitty Hawk – an early, aspirational glimpse at a revolution to come. By providing exponentially greater calculation power than the machines we use today, quantum computers could one day transform the way we communicate ideas, conceal data and comprehend the universe.
The result is also a feather in the cap for both Google and the United States because quantum technology is expected to confer huge economic and national security advantages to whoever can master it first.
The technology community has been abuzz about the breakthrough ever since a leaked version of the study was published on (and then removed from) a NASA website last month. Writing in the magazine Quanta, Caltech theoretical physicist John Preskill called the result “a remarkable achievement in experimental physics and a testament to the brisk pace of progress in quantum computing hardware.”
But the claim has also prompted skepticism from competitors. Researchers at IBM, which has been working on its own quantum machines, argued in a blog post this week that a classical computer system would in fact take two and a half days to perform the calculation in Google’s report – and would make fewer mistakes in the process. The IBM scientists also questioned the use of the James Bond-esque term “quantum supremacy,” which seems to imply that classical computers are about to become obsolete.
Whoever turns out to be right, quantum supremacy is a largely symbolic achievement; the specific task assigned to the Google computer has no practical application.
But Preskill, who coined the term in 2012, wrote in Quanta that he aimed to convey the notion that “this is a privileged time in the history of our planet,” when the most arcane laws of physics might be harnessed for human ambitions.
Scientists have known for a century that the predictable laws of Newtonian physics – objects fall down; matter can only be in one place at one time – fall apart at the atomic and subatomic level.
In this quantum realm, electrons leap instantaneously from one energy state to another. Particles can exist in multiple states at the same time, a phenomenon known as “superposition.” They can also stay connected across large distances, which Einstein called “spooky” and modern physicists call “entanglement.”
With quantum computing, scientists can put these weird, wild particles to work.
Classical computers encode information in “bits,” an electrical or optical pulse that can represent either a 0 or 1. Eight bits constitute a “byte,” which can typically store one character – for example, the letter A, or a dollar sign. The first 8-inch floppy disk held 242,944 bytes. Apple’s new iPhone 11 comes with 64 billion bytes.
The Summit system at Oak Ridge National Lab, a classical supercomputer that takes up two tennis courts’ worth of floor space and can perform 200 quadrillion calculations per second, boasts a whopping 250 petabytes of storage – in bytes, that number comes out to about 250,000,000,000,000,000.
But superposition means that a quantum bit, or qubit, isn’t confined to being either 0 or 1. It can exist as both at once. This means it can carry twice as much information, a power that increases exponentially with each qubit added: Two qubits convey four possible numbers; three are able to carry eight; four is the equivalent of 16. Entanglement further beefs up a system’s computing power by allowing it to perform multiple calculations at once.
By the time you get up to 53 qubits – the size of both Google’s Sycamore processor and a similar machine being built at IBM – you’re approaching the potential of supercomputers like Summit.
That is, if your quantum computer works. A faint noise or a glimmer of heat can alter a superposition, leading to errors. Measuring a particle, or disturbing it in any way, will cause the superposition to “decohere,” or collapse. The qubit becomes an ordinary bit. Add more qubits to a system, and decoherence happens even faster.
That’s what stands between researchers like those at Google and the quantum world they hope to attain. To build an effective quantum computer, scientists must figure out how to create and manipulate entangled qubits that last long enough to actually do something interesting with them.
The possibilities presented by quantum computing are what entice companies and governments to keep plugging away at it.
Several technology companies are competing to create quantum machines; IBM has even made its prototype available online for anyone to use. Last year, President Donald Trump signed into law the National Quantum Initiative Act, which establishes research centers to focus on quantum information science. Meanwhile, China has spent billions on quantum technology development.
The most obvious potential applications of this research are in the realm of national security. Entangled particles could one day be used for “quantum communication” – a means of sending super-secure messages that doesn’t rely on cables or wireless signals. The tremendous processing power of quantum computers might be used to break previously unbreakable codes.
But those are far from the only uses. Biologists might use quantum computers to understand natural processes far too complex for classical machines to simulate. Pharmaceutical researchers could employ them to discover new drugs. Quantum computing promises to generate better artificial intelligence and more effective nanotechnologies.
“Only by challenging the entanglement frontier,” Preskill wrote in 2012, referring to the bleeding edge of quantum research, “will we learn whether Nature provides extravagant resources far beyond what the classical world would allow.”
(c) 2019, The Washington Post · Sarah Kaplan