# Quantum computers are about to get real

**SEEKING QUANTUM SUPREMACY** Google, IBM and others are developing quantum computers. IBM has made its five-qubit computer accessible online for free, and the company is planning a 50-qubit computer for commercial use. The large tank shown here holds the cooling system that keeps a 17-qubit processor cold.

Andy Aaron/IBM Research/Flickr (CC BY-ND Two.0)

Albeit the term “quantum computer” might suggest a miniature, sleek device, the latest incarnations are a far sob from anything available in the Apple Store. In a laboratory just sixty kilometers north of Fresh York City, scientists are running a fledgling quantum computer through its paces — and the entire package looks like something that might be found in a dark corner of a basement. The cooling system that envelops the computer is about the size and form of a household water heater.

Underneath that clunky exterior sits the heart of the computer, the quantum processor, a little, precisely engineered chip about a centimeter on each side. Chilled to temperatures just above absolute zero, the computer — made by IBM and housed at the company’s Thomas J. Watson Research Center in Yorktown Heights, N.Y. — comprises sixteen quantum bits, or qubits, enough for only ordinary calculations.

If this computer can be scaled up, tho’, it could transcend current thresholds of computation. Computers based on the physics of the supersmall can solve puzzles no other computer can — at least in theory — because quantum entities behave unlike anything in a larger area.

Quantum computers aren’t putting standard computers to shame just yet. The most advanced computers are working with fewer than two dozen qubits. But teams from industry and academia are working on expanding their own versions of quantum computers to fifty or one hundred qubits, enough to perform certain calculations that the most powerful supercomputers can’t pull off.

The race is on to reach that milestone, known as “quantum supremacy.” Scientists should meet this objective within a duo of years, says quantum physicist David Schuster of the University of Chicago. “There’s no reason that I see that it won’t work.”

#### Deep freeze

But supremacy is only an initial step, a symbolic marker akin to sticking a flagpole into the ground of an unexplored landscape. The very first tasks where quantum computers prevail will be contrived problems set up to be difficult for a standard computer but effortless for a quantum one. Eventually, the hope is, the computers will become prized instruments of scientists and businesses.

**Attention-getting ideas**

Some of the very first useful problems quantum computers will very likely tackle will be to simulate petite molecules or chemical reactions. From there, the computers could go on to speed the search for fresh drugs or kick-start the development of energy-saving catalysts to accelerate chemical reactions. To find the best material for a particular job, quantum computers could search through millions of possibilities to pinpoint the ideal choice, for example, ultrastrong polymers for use in airplane wings. Advertisers could use a quantum algorithm to improve their product recommendations — dishing out an ad for that fresh cell phone just when you’re on the edge of purchasing one.

Quantum computers could provide a boost to machine learning, too, permitting for almost flawless handwriting recognition or helping self-driving cars assess the flood of data pouring in from their sensors to swerve away from a child running into the street. And scientists might use quantum computers to explore exotic realms of physics, simulating what might happen deep inwards a black slot, for example.

But quantum computers won’t reach their real potential — which will require harnessing the power of millions of qubits — for more than a decade. Exactly what possibilities exist for the long-term future of quantum computers is still up in the air.

The outlook is similar to the patchy vision that surrounded the development of standard computers — which quantum scientists refer to as “classical” computers — in the middle of the 20th century. When they began to tinker with electronic computers, scientists couldn’t fathom all of the eventual applications; they just knew the machines possessed excellent power. From that initial promise, classical computers have become indispensable in science and business, predominant daily life, with handheld smartphones becoming constant companions (SN: Four/1/17, p. Legal).

We’re very excited about the potential to indeed revolutionize … what we can compute.

Since the 1980s, when the idea of a quantum computer very first attracted interest, progress has come in fits and starts. Without the capability to create real quantum computers, the work remained theoretical, and it wasn’t clear when — or if — quantum computations would be achievable. Now, with the petite quantum computers at forearm, and fresh developments coming swiftly, scientists and corporations are preparing for a fresh technology that ultimately seems within reach.

“Companies are truly paying attention,” Microsoft’s Krysta Svore said March thirteen in Fresh Orleans during a packed session at a meeting of the American Physical Society. Enthusiastic physicists packed the room and huddled at the doorways, tightening to hear as she spoke. Svore and her team are exploring what these nascent quantum computers might eventually be capable of. “We’re very excited about the potential to indeed revolutionize … what we can compute.”

**Anatomy of a qubit**

Quantum computing’s promise is rooted in quantum mechanics, the counterintuitive physics that governs lil’ entities such as atoms, electrons and molecules. The basic element of a quantum computer is the qubit (pronounced “CUE-bit”). Unlike a standard computer bit, which can take on a value of zero or 1, a qubit can be 0, one or a combination of the two — a sort of purgatory inbetween zero and one known as a quantum superposition. When a qubit is measured, there’s some chance of getting zero and some chance of getting 1. But before it’s measured, it’s both zero and 1.

Because qubits can represent zero and one at the same time, they can encode a wealth of information. In computations, both possibilities — zero and one — are operated on at the same time, permitting for a sort of parallel computation that speeds up solutions.

Another qubit quirk: Their properties can be intertwined through the quantum phenomenon of entanglement (SN: Four/29/17, p. 8). A measurement of one qubit in an entangled pair instantly exposes the value of its fucking partner, even if they are far apart — what Albert Einstein called “spooky activity at a distance.”

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#### Gated community

In quantum computing, programmers execute a series of operations, called gates, to roll qubits (represented by black horizontal lines), entangle them to link their properties, or put them in a superposition, signifying zero and one at the same time. Very first, some gate definitions:

**X gate**: Rolls a qubit from a zero to a 1, or vice versa.

**Hadamard gate**: Puts a qubit into a superposition of states.

**Managed not gate**: Rolls a 2nd qubit only if the very first qubit is 1.

Scientists can combine gates like the ones above into sophisticated sequences to perform calculations that are not possible with classical computers. One such quantum algorithm, called Grover’s search, speeds up searches, such as scanning fingerprint databases for a match. To understand how this works, consider a plain game demonstrate.

In this game display, four doors hide one car and three goats. A contestant must open a door at random in hopes of finding the car. Grover’s search looks at all possibilities at once and amplifies the desired one, so the contestant is more likely to find the car. The two qubits represent four doors, labeled in binary as 00, 01, ten and 11. In this example, the car is hidden behind door 11.

**Step 1**: Puts both qubits in a superposition. All four doors have equal probability.

**Step Two**: Hides the car behind door 11. In a real-world example, this information would be stored in a quantum database.

**Step Three**: Amplifies the probability of getting the correct reaction, 11, when the qubits are measured.

**Step Four**: Measures both qubits; the result is 11.

Source: IBM Research; Graphics: T. Tibbitts

Such weird quantum properties can make for superefficient calculations. But the treatment won’t speed up solutions for every problem thrown at it. Quantum calculators are particularly suited to certain types of puzzles, the kind for which correct answers can be selected by a process called quantum interference. Through quantum interference, the correct response is amplified while others are canceled out, like sets of ripples meeting one another in a lake, causing some peaks to become larger and others to vanish.

One of the most famous potential uses for quantum computers is violating up large integers into their prime factors. For classical computers, this task is so difficult that credit card data and other sensitive information are secured via encryption based on factoring numbers. Eventually, a large enough quantum computer could break this type of encryption, factoring numbers that would take millions of years for a classical computer to crack.

Quantum computers also promise to speed up searches, using qubits to more efficiently pick out an information needle in a data haystack.

Qubits can be made using a multitude of materials, including ions, silicon or superconductors, which conduct electrical play without resistance. Unluckily, none of these technologies permit for a computer that will fit lightly on a desktop. However the computer chips themselves are lil’, they depend on large cooling systems, vacuum chambers or other bulky equipment to maintain the mild quantum properties of the qubits. Quantum computers will most likely be held to specialized laboratories for the foreseeable future, to be accessed remotely via the internet.

**Going supreme**

That vision of Web-connected quantum computers has already begun to Quantum computing is titillating. It’s coming, and we want a lot more people to be well-versed in itmaterialize. In 2016, IBM unveiled the Quantum Practice, a quantum computer that anyone around the world can access online for free.

Quantum computing is titillating. It’s coming, and we want a lot more people to be well-versed in it.

With only five qubits, the Quantum Practice is “limited in what you can do,” says Jerry Chow, who manages IBM’s experimental quantum computing group. (IBM’s 16-qubit computer is in beta testing, so Quantum Practice users are just beginning to get their palms on it.) Despite its limitations, the Quantum Practice has permitted scientists, computer programmers and the public to become familiar with programming quantum computers — which go after different rules than standard computers and therefore require fresh ways of thinking about problems. “Quantum computing is arousing. It’s coming, and we want a lot more people to be well-versed in it,” Chow says. “That’ll make the development and the advancement even quicker.”

But to fully jump-start quantum computing, scientists will need to prove that their machines can outperform the best standard computers. “This step is significant to coax the community that you’re building an actual quantum computer,” says quantum physicist Simon Devitt of Macquarie University in Sydney. A demonstration of such quantum supremacy could come by the end of the year or in 2018, Devitt predicts.

Researchers from Google set out a strategy to demonstrate quantum supremacy, posted online at arXiv.org in 2016. They proposed an algorithm that, if run on a large enough quantum computer, would produce results that couldn’t be replicated by the world’s most powerful supercomputers.

The method involves performing random operations on the qubits, and measuring the distribution of answers that are slobber out. Getting the same distribution on a classical supercomputer would require simulating the complicated inward workings of a quantum computer. Simulating a quantum computer with more than about forty five qubits becomes unmanageable. Supercomputers haven’t been able to reach these quantum wilds.

To inject this hinterland, Google, which has a nine-qubit computer, has aggressive plans to scale up to forty nine qubits. “We’re pretty optimistic,” says Google’s John Martinis, also a physicist at the University of California, Santa Barbara.

Martinis and colleagues plan to proceed in stages, working out the kinks along the way. “You build something, and then if it’s not working exquisitely well, then you don’t do the next one — you fix what’s going on,” he says. The researchers are presently developing quantum computers of fifteen and twenty two qubits.

IBM, like Google, also plans to go big. In March, the company announced it would build a 50-qubit computer in the next few years and make it available to businesses anxious to be among the very first adopters of the burgeoning technology. Just two months later, in May, IBM announced that its scientists had created the 16-qubit quantum computer, as well as a 17-qubit prototype that will be a technological jumping-off point for the company’s future line of commercial computers.

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But a quantum computer is much more than the sum of its qubits. “One of the real key aspects about scaling up is not simply … qubit number, but indeed improving the device spectacle,” Chow says. So IBM researchers are focusing on a standard they call “quantum volume,” which takes into account several factors. These include the number of qubits, how each qubit is connected to its neighbors, how quickly errors slip into calculations and how many operations can be performed at once. “These are all factors that truly give your quantum processor its power,” Chow says.

Errors are a major obstacle to boosting quantum volume. With their soft quantum properties, qubits can accumulate glitches with each operation. Qubits must stand against these errors or calculations quickly become unreliable. Eventually, quantum computers with many qubits will be able to fix errors that crop up, through a procedure known as error correction. Still, to boost the complexity of calculations quantum computers can take on, qubit reliability will need to keep improving.

Different technologies for forming qubits have various strengths and weaknesses, which affect quantum volume. IBM and Google build their qubits out of superconducting materials, as do many academic scientists. In superconductors cooled to utterly low temperatures, electrons flow unimpeded. To style superconducting qubits, scientists form circuits in which current flows inwards a loop of wire made of aluminum or another superconducting material.

Several teams of academic researchers create qubits from single ions, trapped in place and probed with lasers. Intel and others are working with qubits fabricated from lil’ bits of silicon known as quantum dots (SN: 7/11/15, p. 22). Microsoft is studying what are known as topological qubits, which would be extra-resistant to errors creeping into calculations. Qubits can even be forged from diamond, using defects in the crystal that isolate a single electron. Photonic quantum computers, meantime, make calculations using particles of light. A Chinese-led team demonstrated in a paper published May one in Nature Photonics that a light-based quantum computer could outperform the earliest electronic computers on a particular problem.

One company, D-Wave, claims to have a quantum computer that can perform serious calculations, albeit using a more limited strategy than other quantum computers (SN: 7/26/14, p. 6). But many scientists are skeptical about the treatment. “The general consensus at the moment is that something quantum is happening, but it’s still very unclear what it is,” says Devitt.

**Identical ions**

While superconducting qubits have received the most attention from giants like IBM and Google, underdogs taking different approaches could eventually pass these companies by. One potential upstart is Chris Monroe, who crafts ion-based quantum computers.

On a walkway near his office on the University of Maryland campus in College Park, a banner featuring a larger-than-life portrait of Monroe adorns a fence. The message: Monroe’s quantum computers are a “fearless idea.” The banner is part of an advertising campaign featuring several of the university’s researchers, but Monroe seems an apt choice, because his research bucks the trend of working with superconducting qubits.

Monroe and his petite army of researchers arrange ions in neat lines, manipulating them with lasers. In a paper published in Nature in 2016, Monroe and colleagues debuted a five-qubit quantum computer, made of ytterbium ions, permitting scientists to carry out various quantum computations. A 32-ion computer is in the works, he says.

Monroe’s labs — he has half a dozen of them on campus — don’t resemble anything normally associated with computers. Tables hold an indecipherable mess of lenses and mirrors, surrounding a vacuum chamber that houses the ions. As with IBM’s computer, albeit the total package is bulky, the quantum part is minuscule: The chain of ions spans just hundredths of a millimeter.

Scientists in laser goggles tend to the entire setup. The foreign nature of the equipment explains why ion technology for quantum computing hasn’t taken off yet, Monroe says. So he and colleagues took matters into their own mitts, creating a start-up called IonQ, which plans to refine ion computers to make them lighter to work with.

Monroe points out a few advantages of his technology. In particular, ions of the same type are identical. In other systems, little differences inbetween qubits can muck up a quantum computer’s operations. As quantum computers scale up, Monroe says, there will be a big price to pay for those petite differences. “Having qubits that are identical, over millions of them, is going to be truly significant.”

In a paper published in March in Proceedings of the National Academy of Sciences, Monroe and colleagues compared their quantum computer with IBM’s Quantum Practice. The ion computer performed operations more leisurely than IBM’s superconducting one, but it benefited from being more interconnected — each ion can be entangled with any other ion, whereas IBM’s qubits can be entangled only with adjacent qubits. That interconnectedness means that calculations can be performed in fewer steps, helping to make up for the slower operation speed, and minimizing the chance for errors.

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#### Quantum vs. quantum

Two different quantum computers — one using ion qubits, the other superconducting qubits — went head-to-head in a latest comparison. Both five-qubit computers performed similarly, but each had its own advantages: The superconducting computer was quicker; the ion computer was more interconnected, needing fewer steps to perform calculations.