31 August 2013

Quantum computing videos help explain the next frontier in computation

PHD Comics is almost absurdly popular with the higher-education crowd, dramatizing the ultimate set of first world problems with an incisive, long-suffering wit that resonates with grad students everywhere. A few years ago, creator Jorge Cham decided to widen the appeal of the PHD brand and start making animated explainers for all sorts topics in science, from coffee to bees to, most recently, the dizzying realities of modern quantum science. It used to be that all you needed to do to talk about the frontiers of quantum research was regurgitate a few thought experiments about cats in boxes, but in the past few years the pure science has started to pay practical dividends. That’s the quantum computer, and its most basic principles are explained in a cute, approachable way in the video below.

For the video Cham interviews John Preskill, co-director of the Institute for Quantum Information and Matter, and Spiros Michalakis, a post-doc in quantum studies at Caltech. They explain the nature of the qubit, the ideas behind quantum computers, and the problems faced by the technology going forward.

Most readers of ExtremeTech are probably familiar with the basic principle of superposition — that a quantum bit of information would not exist as either a 1 or a 0, but as both a 1 and a 0 until observed. A classical computer can hold n bits of information in any one of 2n possible combinations; four bits can have any one of sixteen possible states. On the other hand, a quantum computer can hold n qubits in all of 2n possible states; four bits can have all of those sixteen possible states at once.

However, we all know that if you check on Schrödinger’s cat you’ll have either a live or dead cat — observation “collapses” the superposition of states (1 and 0 becomes 1 or 0, dead and alive becomes dead or alive.) Preskill and Michalakis discuss the problem of quantum decoherence, which is basically the problem of information leakage — and they’re not just talking about spies trying to record the computer’s actions. Any interaction with anything outside the system counts as leakage and will cause the whole thing to fall apart — your quantum computer becomes a bundle of useless, unconnected spin units that can’t even operate as well as a traditional digital computer.

They take care to remind us, though, that a quantum computation must eventually spit out a classical answer for our use. This means that only the final answer of a calculation will be visible to us, not the computational path taken by the quantum computer to achieve that answer. Even asking the computer to explain its process after the fact is impossible, since any hypothetical way of keeping a record of the computer’s actions would involve interaction with that recording device and thus cause decoherence. Cham coins the term “quanfidential” to describe the secrecy that computational processes must maintain. As Preskill puts it, this problem of decoherence is what makes developing a working quantum computer so challenging.

This fantastic (though slightly less entertaining) interview with D-Wave Systems scientist Eric Ladizinsky talks about the history of creating the first workable quantum “transistors,” devices that can actually fulfill the requirements of superposition, and even a bit about arranging these incredible devices in an array capable of doing actual computation. D-Wave claimed to have created the world’s first working quantum computer as early as 2007, and in 2011 released the first commercial quantum computer, named the D-Wave One.

Now, quantum computing is real enough to have attracted the attention of the world’s most influential contractors. Lockheed Martin recently signed a deal with D-Wave to develop quantum computers to solve its most hated computational problems. Just a few months ago, a prototype of the D-Wave Two (with only 439 of the 512 qubits projected for the project) performed a particular calculation 3,600 times faster than top-end conventional workstations — though it was built from the ground up for that type of calculation, so perhaps the comparison is a bit unfair.

Regardless, quantum computing is coming. The power is increasing incredibly quickly (the D-Wave Two can theoretically be as much as 4×10115 times as powerful as the D-Wave One) as is the cost of creating them. One quantum computer recently revealed the lowest-energy folding state of a protein — but again, it was built specifically to do this. How exactly one would go about programming all-purpose quantum software — let alone a quantum operating system — is currently unclear, but those are the questions that are becoming relevant.

It’s time for the public to start grappling with the premise of a technology that’s poised to revolutionize their world.

Now read: New discovery may make encryption ‘exponentially easier’ to break


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