Equilibrium Networks

Science has just published a paper by Dave Wineland’s group at NIST that describes an experimental implementation of

a combination of all the fundamental elements required to perform scalable quantum computing using qubits stored in the internal states of trapped atomic ions.

(Technology Review has a layman’s overview here.)

It has been eight years since I really kept up with quantum computing, but this result is clearly very important. I recall hearing about the idea of a “quantum bus” to shuttle ions back and forth in order to scale up ion trap quantum computing at a dinner that I was at along with Wineland in 2000, and the idea appears to date from 1998 or even earlier. There were no obvious showstoppers, his group (among others) was good and certain to be adequately funded for as long as it would take, and so it is not that big a surprise to see this working now.

But even though the transport of ions in traps had been done before, this current result has built on of over a decade of work. An idea apparently developed over the last few years that I don’t recall from those early days (it seems to date from a 2003 paper) involves using Mg⁺ “refrigerator” ions to sympathetically cool qubit-carrying Be⁺ ions by

using a combination of Doppler cooling and resolved sideband cooling on the ²⁴Mg⁺ ions. Importantly, the cooling light only interacts with ²⁴Mg⁺, leaving the qubits stored in ⁹Be⁺ intact.

Although the fact that it took so long for them to get here indicates just how difficult the physics and engineering challenges are, more results extending this work (probably starting with improving the fidelity, with longer-term goals of working with multidimensional trap arrays and finding good ways to scale up the entanglement distribution) are certain to follow.

In the last paragraph of a review paper on quantum algorithms and protocols I wrote in 2000, I said that “it is appropriate to say some words about whether a scalable quantum computer will in fact ever be built. [I believe] that such devices could well be built within 20 years.” The Wineland group’s latest result makes me feel better about that statement (and worse about using RSA for anything long-term) than I have in the last couple of years.

Update: Speaking of “certain to be adequately funded for as long as it would take”, I just noticed a Nature article from June talking about IARPA cutting funding to Wineland’s group. From the article:

In 2007, the newly created IARPA took over funding for quantum information science from the National Security Agency. The following year, IARPA stopped funding the NIST researchers because, it says, it did not want to fund other government agencies…the NIST funds ran out while [IARPA] managers were reviewing the programme and deciding how NIST might be involved.

While IARPA’s stance is understandable, this sort of disruption is not conducive to National Medal of Science-level work, even if as NIST said

It’s ultimately the responsibility of NIST to make sure these programmes receive the resources they need, and we are committed to ensuring they remain adequately funded.

This entry was posted on Sunday, August 9th, 2009 at 14:27 and is filed under Commentary, Nonrandom bits, Science. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.