people make given the choices of others. Imagine, for instance, a quantum version of the “public goods” game discussed in earlier chapters. The idea is that a neighborhood group proposes building a project of public benefit, such as a park, to be paid for by voluntary contributions. Presumably people who want the park will contribute the most money to the fund drive. But standard game theory suggests that many people who want the park will contribute little or no money, reasoning that others will fork over enough to pay for it. Therefore it’s hard to get donations, even for a park everybody desires, without the intervention of some outside agency (say, a tax collector).

In 2003, scientists from HP Labs in Palo Alto, California, posted a paper on the Internet showing how a quantum public goods game provides strategies that reduce the temptation to free-load. When people make economic or social decisions, they don’t always choose based on self-interest alone, but may be influenced by social norms and expectations—sort of the way properties of a photon are influenced by distant measurements. So if you send your pledge via a quantum information channel, its message can depend on the messages from the other contributors. Therefore, the HP scientists suggested, entangled photons transmitted by laser beams through optical fibers could in theory be used for pledging donations in real-life community projects. Using quantum-entangled photons to communicate their intentions could allow a coordination of commitments that otherwise couldn’t be guaranteed.

“Quantum mechanics offers the ability to solve the free-rider problem in the absence of a third-party enforcer,” wrote Kay-Yut Chen, Tad Hogg, and Raymond Beausoleil in their paper.8


The same principle could be applied to other sorts of community communication issues, including voting, especially in elections with multiple candidates. You wouldn’t need runoffs, since the multiple possible outcomes could be encoded in quantum information.

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