The Quantum Computing Revolution

Qubits or Not Qubits?
E-mail debates of newsworthy topics.
May 15 2003 2:41 PM

The Quantum Computing Revolution


Dear Bob,

I'm afraid America (or the small subset reading this exchange) will just have to wait until it becomes clearer to everybody how this new invention comes to market. The state-of-the-art seven-atom quantum computers that have been tinkered with at Los Alamos, Stanford, IBM, and elsewhere are so delicate that they must be operated at temperatures near absolute zero. So, for now, these invisibly small calculators must be surrounded by a room full of expensive cooling equipment. That's the nature of the quantum bits, or "qubits" as they are called—touch them, or even look at them the wrong way, and they become scrambled into pure noise.

Barring some unforeseen breakthrough, the first quantum computers powerful enough to crack important codes might cost tens of millions of dollars and be attended by a round-the-clock staff of operators. A quantum calculating factory like that is certainly more within the reach of a Pentagon or a Microsoft than an India, a Pakistan, or even a well-heeled terrorist cell.

So, my guess is that quantum codebreaking, if they can bring it out of the lab, would indeed be another case of the rich becoming more powerful and more deeply entrenched. And that advantage could last a long time. This is a technology that might take many years to reach our desktops, if it gets there at all.

But, as you suggest, quantum cryptography is the wildcard. Harnessing quantum weirdness to protect codes is way cheaper and easier than using it to break them, and that may prove more decisive than any trickle-down effect.

Still there are some glitches to sending secret quantum communications. The farther the signal has to travel, the weaker it becomes. And because of the perversity of quantum mechanics, you cannot use signal-enhancing "repeaters" to boost the message along the way. (To amplify the qubits you have to measure them, which scrambles the message.)

The exciting or (from the perspective of your last post) scary thing about quantum computing is that nothing in the laws of physics rules it out. And "proof of principle" experiments, like factoring the number 15 quantum-mechanically, show that what is possible in theory is also within technological reach.

On a small scale, anyway. Nothing in the laws of physics rules out fusion energy as a source of clean, limitless electrical power. And yet after decades of research costing many millions of dollars, the best we can do is to sustain a reaction for a tiny fraction of a second. Sustaining a quantum calculation long enough to break codes could be just as challenging. But the incentive is certainly there.

I have to hand it to you, Bob. I hadn't expected the conversation to veer this way. Once again you have my brain spinning in a new direction. It was your first book, Three Scientists and Their Gods, that really got me thinking about this strange stuff called information, the 1's and 0's that (depending on your philosophical bias) either reflect or make up the world.

It may have been in your book that I came across Gregory Bateson's definition of information: "a difference that makes a difference." So, to address your final point, the effect you describe is spooky, it is an action, and it happens at a distance. But whatever it is that passes instantaneously from Bob to George, from Nuevo York to Nuevo Mexico, couldn't be used to send a message. So, it's not information. Not even quantum mechanics will let us subvert the speed of light (even if it does promise, for some otherwise endless calculations, a shortcut through time).

But none of the above rules out a lot of other astonishments. You probably have read that Roger Penrose, another Oxford physicist extraordinaire, believes the brain itself is a quantum computer. But let's save that for another day. Thank you for such a stimulating conversation.



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