MIT’s Seth Lloyd has given some thought to the design options for quantum networks. He says, “Networks using cesium-atom ensembles are one of the most promising technologies for transporting quantum information over long distances.” Yet the ensemble approach is relatively bulky, and the larger a quantum system, the greater the problems for computing. Lloyd says, “Circuit-based approaches like superconducting loops are more scalable within a small space, with potentially large numbers of qubits on one circuit board.” But such systems are unsuitable for communications. “Kimble and I have collaborated on concepts using individual atoms instead of ensembles,” he says. “If we could move information between atomic ensembles and individual ions and ion traps, that’s a scalable quantum technology.” A plausible scenario, according to Lloyd, seems to be to use ensembles for communications and the more localized, scalable quantum devices, like the superconducting loops or the ion traps, for computation.
So Kimble has a reasonable argument that quantum networks are feasible. And the advantages that he envisions–absolute data security, no latency, and a further exponential gain in computational power–would hardly be negligible in the world of information commerce.
Some commercial applications of quantum information technology are fairly obvious. Human stock traders have come to rely on the computerized trading programs known as high-frequency traders (HFTs). On some days, these generate more than half the volume on the New York Stock Exchange. Major trading institutions have spent millions developing their algorithms to analyze market data and execute large numbers of trades according to strategies that are, mostly, sophisticated variations on buying microseconds after some data arrives and then selling microseconds later at the expense of other traders who couldn’t get the data in or their trades out as rapidly. Futures traders who use near-instantaneous quantum networks will have clear advantages over those who don’t.
Other commercial applications are possible as well. Scott Aaronson suggested one of them in a paper called “Quantum Copy-Protection and Quantum Money.” He observed that quantum states cannot be copied because any measurement process destroys them, which “raises the possibility of using quantum states as unclonable information.” Exploiting this possibility will require circumventing the fact that quantum states collapse under measurement and creating, first (for purposes of quantum money), unclonable states that can be verified as authentic, and second (for purposes of quantum copy protection), unclonable states that would still allow the protected software, DVDs, CDs, and so on to be used. Aaronson demonstrated that at least one type of publicly verifiable quantum money and two schemes for quantum-based copy protection are theoretically feasible–raising the possibility, for the first time ever, of absolutely uncounterfeitable money and insurmountable digital-rights protection.
The first generation of money emerged with the invention of coins in Lydia nearly 3,000 years ago, its second generation with the paper bills of exchange issued by the banks of Renaissance Italy, and its third with electronic money and the virtual economy of the modern era. If scientists like Kimble and Aaronson are correct, quantum networks may soon give rise to a further generation of money.
Mark Williams is a contributing editor to Technology Review.