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Computers could be much more powerful than previously realized

Quantum computers promise huge speedups on some computational problems because they harness a strange physical property called entanglement, in which the physical state of one tiny particle depends on measurements made of another. In quantum computers, entanglement is a computational resource, roughly like a chip’s clock cycles — kilohertz, megahertz, gigahertz — and memory in a conventional computer.

In a recent paper in the journal Proceedings of the National Academy of Sciences, researchers at MIT and IBM’s Thomas J. Watson Research Center show that simple systems of quantum particles exhibit exponentially more entanglement than was previously believed. That means that quantum computers — or other quantum information devices — powerful enough to be of practical use could be closer than we thought.

Where ordinary computers deal in bits of information, quantum computers deal in quantum bits, or qubits. Previously, researchers believed that in a certain class of simple quantum systems, the degree of entanglement was, at best, proportional to the logarithm of the number of qubits.

“For models that satisfy certain physical-reasonability criteria — i.e., they’re not too contrived; they’re something that you could in principle realize in the lab — people thought that a factor of the log of the system size was the best you can do,” says Ramis Movassagh, a researcher at Watson and one of the paper’s two co-authors. “What we proved is that the entanglement scales as the square root of the system size. Which is really exponentially more.”

That means that a 10,000-qubit quantum computer could exhibit about 10 times as much entanglement as previously thought. And that difference increases exponentially as more qubits are added.

Logical or physical?

This matters because of the distinction, in quantum computing, between logical qubits and physical qubits. A logical qubit is an abstraction used to formulate quantum algorithms; a physical qubit is a tiny bit of matter whose quantum states are both controllable and entangled with those of other physical qubits.

A computation involving, say, 100 logical qubits would already be beyond the capacity of all the conventional computers in the world. But with most of today’s theoretical designs for general-purpose quantum computers, realizing a single logical qubit requires somewhere around 100 physical qubits. Most of the physical qubits are used for quantum error correction and to encode operations between logical qubits.

Since preserving entanglement across large groups of qubits is the biggest obstacle to developing working quantum devices, extracting more entanglement from smaller clusters of qubits could make quantum computing devices more practical.

Qubits are analogous to bits in a conventional computer, but where a conventional bit can take on the values 0 or 1, a qubit can be in “superposition,” meaning that it takes on both values at once. If qubits are entangled, they can take on all their possible states simultaneously. One qubit can take on two states, two qubits four, three qubits eight, four qubits 16, and so on. It’s the ability to, in some sense, evaluate computational alternatives simultaneously that gives quantum computers their extraordinary power.

Publicly traded corporation

Cook joined Apple in 1998 and was named its CEO in 2011. As chief executive, he has overseen the introduction of some of Apple’s innovative and popular products, including iPhone 7 and Apple Watch. An advocate for equality and champion of the environment, Cook reminds audiences that Apple’s mission is to change the world for the better, both through its products and its policies.

“Mr. Cook’s brilliance as a business leader, his genuineness as a human being, and his passion for issues that matter to our community make his voice one that I know will resonate deeply with our graduates,” MIT President L. Rafael Reif says. “I am delighted that he will join us for Commencement and eagerly await his charge to the Class of 2017.”

Before becoming CEO, Cook was Apple’s chief operating officer, responsible for the company’s worldwide sales and operations, including management of Apple’s global supply chain, sales activities, and service and support. He also headed the Macintosh division and played a key role in the development of strategic reseller and supplier relationships, ensuring the company’s flexibility in a demanding marketplace.

“Apple stands at the intersection of liberal arts and technology, and we’re proud to have many outstanding MIT graduates on our team,” Cook says. “We believe deeply that technology can be a powerful force for good, and I’m looking forward to speaking to the Class of 2017 as they look ahead to making their own mark on the world.”

Prior to joining Apple, Cook was vice president of corporate materials at Compaq, responsible for procuring and managing product inventory. Before that, he served as chief operating officer of the Reseller Division at Intelligent Electronics.

Cook also spent 12 years with IBM, ending as director of North American fulfillment, where he led manufacturing and distribution for IBM’s personal computer company in North and Latin America.

Cook earned a BS in industrial engineering from Auburn University in 1982, and an MBA from Duke University in 1988.

“Tim Cook is a trailblazer and an inspiration to innovators worldwide,” says Liana Ilutzi, president of MIT’s Class of 2017. “He represents the best of the entrepreneurial and fearless spirit of the MIT community. While faithfully maintaining his integrity and humility, Tim runs one of the most influential companies on the planet. We are beyond excited to have him with us for Commencement!”

“We are looking forward to hearing Tim Cook speak at Commencement,” says Graduate Student Council President Arolyn Conwill. “We believe that his innovative leadership at Apple, along with his commitment to advocacy on sustainability, security, and equality, will inspire graduates to make a far-reaching, positive impact on the world.”

Cook joins a list of notable recent MIT Commencement speakers, including actor and filmmaker Matt Damon (2016); U.S. Chief Technology Officer Megan Smith ’86 SM ’88 (2015); DuPont CEO Ellen Kullman (2014); Dropbox co-founder and CEO Drew Houston ’05 (2013); and Khan Academy founder Sal Khan ’98, MEng ’98 (2012).

“I am delighted with the selection of Tim Cook as the Commencement speaker,” says Chancellor for Academic Advancement Eric Grimson, the longstanding chair of MIT’s Commencement Committee. “Apple is widely viewed as a company that champions innovation, that seeks creative and inventive solutions to problems across a wide range of domains, and that looks to balance technology with issues of social good. These are all themes that are of great importance to our graduates, and I am sure his remarks will be an inspiration to them.”