(Bloomberg) -- Satya Nadella, the chief executive officer of Microsoft Corp., calls quantum computing one of three emerging technologies that will radically reshape the world, along with artificial intelligence and augmented reality. But it’s easier to describe quantum computing’s importance -- that is, its potential importance, because it barely exists now -- than to say what it is. Understanding quantum mechanics, whose principles underpin quantum computing, involves a lot of mental mountain climbing. Something about a cat in a box that might or might not be dead? Not to worry: The basics of quantum computing aren’t as complicated as you might think.
1. What is a quantum computer?
One that uses quantum mechanical properties to perform its calculations. These devices were first conceived in the early 1980s by, among others, Nobel Prize-winning physicist Richard Feynman. But it was only in the late 1990s that the first rudimentary quantum computers were built by academic researchers. And it is only in the past decade that progress has been made toward creating larger, more powerful machines.
2. What’s their appeal?
In the long run, they might make today’s fastest supercomputer look like an abacus. Tasks that seem more in reach are creating more efficient chemical catalysts, optimizing the risk and return of financial portfolios, creating less data-hungry machine learning models, improving supply chains and helping discover new drugs.
3. Who’s building them?
D-Wave Systems Inc., a Canadian company, became the first to sell quantum computers in 2011, although their usefulness is limited to certain kinds of math problems. IBM, Google, Intel and Rigetti Computing, a startup in Berkeley, California, have all created working quantum computers and sell time on them to businesses and researchers through the cloud. Intel has started shipping a superconducting quantum chip to researchers. And it has also created a much smaller – but so far less powerful quantum computer -- that runs on a silicon chip that’s not all that different from those found in normal computers. Microsoft has a well-funded program to build a quantum computer using an unusual design that might make it more practical for commercial applications. Meanwhile, China is building a $10 billion National Laboratory for Quantum Information Sciences as part of a big push in the field.
4. How do quantum computers work?
Quantum computers use tiny circuits to perform calculations, a bit like normal computers. But they also use two mind-bending quantum phenomena called superposition and entanglement. Regular computers process information in units called bits, which can represent one of two possible states -- 0 or 1 -- that correspond to whether a tiny portion of the computer chip called a logic gate is open or closed. By contrast, quantum computers use quantum bits, or qubits. Qubits can represent both a 0 and 1 at the same time. So two qubits can represent four numbers simultaneously, and three qubits can represent eight numbers, and so on. That’s superposition.
5. OK, what’s entanglement?
In designing a standard computer, engineers spend a lot of time trying to make sure the status of each bit is independent from those of all the other bits. But in a quantum computer, each qubit influences the other qubits around it, working together to arrive at a solution. Superposition and entanglement are what give quantum computers the ability to process so much more information so much faster than classical computers.
6. What’s the quantum version of a silicon logic gate?
There’s no one answer, which is why competing projects take such technically varied approaches. In theory, anything that exhibits quantum mechanical properties that can be controlled could be used to make qubits.
7. How are different projects trying to make them?
IBM, D-Wave and Alphabet Inc.’s Google use tiny loops of superconducting wire, others use semiconductors and some use a combination of both semiconducting and superconducting materials. Some scientists have created qubits from the spin of electrons, trapped ions or pulses of photons. Microsoft is taking yet another tack, trying to twist elusive subatomic particles called Majorana fermions into a braided shape that would keep qubits in a quantum state longer. Many of these qubits can only exist under very specialized conditions, such as temperatures 180 times colder than those found in deep space.
8. When do I get my quantum computer?
Not anytime soon, for two reasons, one of which is computing power. Among the universal quantum computers built so far (universal meaning not limited to solving only certain kinds of mathematical problems), Google has the biggest, with 72 qubits, while IBM and Intel have created ones with about 50 qubits. Google’s is close to the point at which these machines will be able to do something that a classical computer cannot, a milestone known as "quantum supremacy." But even those first applications may be very specialized – useful for applications in chemistry or physics, but little else. D-Wave’s latest quantum computer has 2,000 qubits and costs $15 million. It’s working on a 4,000 qubit model, but its design means it can’t be used on a wide range of applications.
9. What’s the other problem?
Errors, lots of them. Scientists have only been able to keep qubits in a quantum state for fractions of a second -- in many cases, too short a period of time to run an entire algorithm. And as the qubits fall out of a quantum state, errors creep into their calculations. These errors have to be corrected with the addition of yet more qubits, but doing so can consume so much computing power that it negates the advantage of using a quantum computer in the first place. In theory, Microsoft’s design should be more accurate -- but so far it hasn’t succeeded in producing even a single working qubit.
10. So, what have we gotten out of this all so far?
Plenty. Not only is quantum computing research pushing the boundaries of fundamental science, but computer scientists are looking at families of algorithms that will be well-suited to run on quantum computers when they do exist. Others are looking at ways to simulate quantum computers on classical computers, efforts that are already yielding some benefits. Companies such as Cambridge Quantum Computing, 1Qbit, QxBranch, and QC Ware specialize in these algorithms and Microsoft, IBM, Google and Rigetti all have researchers working on them too.
The Reference Shelf
- A Bloomberg News article on what’s meant by "quantum supremacy."
- The MIT Technology Review looks at possible uses of quantum computers.
- An overview of the subject by The Economist and a Financial Times explainer.
- A Bloomberg View editorial on the feasibility of quantum computers.
- Bloomberg News articles on the computing arms race and Canada’s quantum brain trust.
- Goldman Sach’s video explainer of the possible applications of quantum computers.
- IBM’s beginner’s guide to quantum computers.
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