First, accepted explanations of the subatomic world turned out to be incomplete. Electrons and other particles didnt just neatly carom around like Newtonian billiard balls, for example. Sometimes they acted like waves instead. Quantum mechanics emerged to explain such quirks, but introduced troubling questions of its own. To take just one brow-wrinkling example, this new math implied that physical properties of the subatomic world, like the position of an electron, didnt really exist until they were observed.

Quantum Leaps

1980

Physicist Paul Benioff suggests quantum mechanics could be used for computation.

1981

Nobel-winning physicist Richard Feynman, at Caltech, coins the term quantum computer.

1985

Physicist David Deutsch, at Oxford, maps out how a quantum computer would operate, a blueprint that underpins the nascent industry of today.

1994

Mathematician Peter Shor, at Bell Labs, writes an algorithm that could tap a quantum computers power to break widely used forms of encryption.

2007

D-Wave, a Canadian startup, announces a quantum computing chip it says can solve Sudoku puzzles, triggering years of debate over whether the companys technology really works.

2013

Google teams up with NASA to fund a lab to try out D-Waves hardware.

2014

Google hires the professor behind some of the best quantum computer hardware yet to lead its new quantum hardware lab.

2016

IBM puts some of its prototype quantum processors on the internet for anyone to experiment with, saying programmers need to get ready to write quantum code.

2017

Startup Rigetti opens its own quantum computer fabrication facility to build prototype hardware and compete with Google and IBM.

If you find that baffling, youre in good company. A year before winning a Nobel for his contributions to quantum theory, Caltechs Richard Feynman remarked that nobody understands quantum mechanics. The way we experience the world just isnt compatible. But some people grasped it well enough to redefine our understanding of the universe. And in the 1980s a few of themincluding Feynmanbegan to wonder if quantum phenomena like subatomic particles' dont look and I dont exist trick could be used to process information. The basic theory or blueprint for quantum computers that took shape in the 80s and 90s still guides Google and others working on the technology.

Before we belly flop into the murky shallows of quantum computing 0.101, we should refresh our understanding of regular old computers. As you know, smartwatches, iPhones, and the worlds fastest supercomputer all basically do the same thing: they perform calculations by encoding information as digital bits, aka 0s and 1s. A computer might flip the voltage in a circuit on and off to represent 1s and 0s for example.

Quantum computers do calculations using bits, too. After all, we want them to plug into our existing data and computers. But quantum bits, or qubits, have unique and powerful properties that allow a group of them to do much more than an equivalent number of conventional bits.

Qubits can be built in various ways, but they all represent digital 0s and 1s using the quantum properties of something that can be controlled electronically. Popular examplesat least among a very select slice of humanityinclude superconducting circuits, or individual atoms levitated inside electromagnetic fields. The magic power of quantum computing is that this arrangement lets qubits do more than just flip between 0 and 1. Treat them right and they can flip into a mysterious extra mode called a superposition.

You may have heard that a qubit in superposition is both 0 and 1 at the same time. Thats not quite true and also not quite falsetheres just no equivalent in Homo sapiens humdrum classical reality. If you have a yearning to truly grok it, you must make a mathematical odyssey WIRED cannot equip you for. But in the simplified and dare we say perfect world of this explainer, the important thing to know is that the math of a superposition describes the probability of discovering either a 0 or 1 when a qubit is read outan operation that crashes it out of a quantum superposition into classical reality. A quantum computer can use a collection of qubits in superpositions to play with different possible paths through a calculation. If done correctly, the pointers to incorrect paths cancel out, leaving the correct answer when the qubits are read out as 0s and 1s.

Jargon for the Quantum Qurious

What's a qubit?

A device that uses quantum mechanical effects to represent 0s and 1s of digital data, similar to the bits in a conventional computer.

What's a superposition?

It's the trick that makes quantum computers tick, and makes qubits more powerful than ordinary bits. A superposition is in an intuition-defying mathematical combination of both 0 and 1. Quantum algorithms can use a group of qubits in a superposition to shortcut through calculations.

What's quantum entanglement?

A quantum effect so unintuitive that Einstein dubbed it spooky action at a distance. When two qubits in a superposition are entangled, certain operations on one have instant effects on the other, a process that helps quantum algorithms be more powerful than conventional ones.

What's quantum speedup?

The holy grail of quantum computinga measure of how much faster a quantum computer could crack a problem than a conventional computer could. Quantum computers arent well-suited to all kinds of problems, but for some they offer an exponential speedup, meaning their advantage over a conventional computer grows explosively with the size of the input problem.

For some problems that are very time consuming for conventional computers, this allows a quantum computer to find a solution in far fewer steps than a conventional computer would need. Grovers algorithm, a famous quantum search algorithm, could find you in a phone book with 100 million names with just 10,000 operations. If a classical search algorithm just spooled through all the listings to find you, it would require 50 million operations, on average. For Grovers and some other quantum algorithms, the bigger the initial problemor phonebookthe further behind a conventional computer is left in the digital dust.

The reason we dont have useful quantum computers today is that qubits are extremely finicky. The quantum effects they must control are very delicate, and stray heat or noise can flip 0s and 1s, or wipe out a crucial superposition. Qubits have to be carefully shielded, and operated at very cold temperatures, sometimes only fractions of a degree above absolute zero. Most plans for quantum computing depend on using a sizable chunk of a quantum processors power to correct its own errors, caused by misfiring qubits.

Recent excitement about quantum computing stems from progress in making qubits less flaky. Thats giving researchers the confidence to start bundling the devices into larger groups. Startup Rigetti Computing recently announced it has built a processor with 128 qubits made with aluminum circuits that are super-cooled to make them superconducting. Google and IBM have announced their own chips with 72 and 50 qubits, respectively. Thats still far fewer than would be needed to do useful work with a quantum computerit would probably require at least thousandsbut as recently as 2016 those companies best chips had qubits only in the single digits. After tantalizing computer scientists for 30 years, practical quantum computing may not exactly be close, but it has begun to feel a lot closer.

What the Future Holds for Quantum Computing

Some large companies and governments have started treating quantum computing research like a raceperhaps fittingly its one where both the distance to the finish line and the prize for getting there are unknown.

Google, IBM, Intel, and Microsoft have all expanded their teams working on the technology, with a growing swarm of startups such as Rigetti in hot pursuit. China and the European Union have each launched new programs measured in the billions of dollars to stimulate quantum R&D. And in the US, the Trump White House has created a new committee to coordinate government work on quantum information science. Several bills were introduced to Congress in 2018 proposing new funding for quantum research, totalling upwards of $1.3 billion. Its not quite clear what the first killer apps of quantum computing will be, or when they will appear. But theres a sense that whoever is first make these machines useful will gain big economic and national security advantages.

More:

What Is Quantum Computing? The Complete WIRED Guide

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