It seems we have another entertaining quantum effect to contend with.

This one is related to the well-known quantum Zeno effect, which occurs when a quantum system is frequently measured. Each measurement essentially resets the quantum system so, in principle, measuring the state of a quantum object often enough can maintain it in a particular state forever.

In essence, it is a quantum version of “the watched pot never boils” phenomenon and was first measured in the lab some 10 years ago.

Its cousin, the quantum anti-Zeno effect, is less well known. In this case, a series of measurements on a quantum system can increase its likelihood of decay so that it changes state more quickly. In this scenario, a watched pot boils more quickly.

Now Vladan Pankovic, a physicist at the University of Novi Sad in Serbia, has come up with a third way in which measurements can influence a quantum system. Pankovic has calculated that a particular sequence of measurements can leave a quantum system in a state in which the probability of decay does not converge.

In other words, there is no way of determining the probability of decay and the system is left with the dilemma of whether to decay or not to decay.

Hence Pankovic’s name for this phenomenon: the quantum Hamlet effect (which may turn out to be more useful and famous than either of its cousins).

Exit Pankovic stage left, chased by bear.

Ref: arxiv.org/abs/0908.1301: Quantum Hamlet Effect