Cup of Java Quantum Computer

One day while looking into her cup of java, Laura realized that this slurry of caffeine molecules could be the world’s natural quantum computer. How could this inherent ability in coffee be possible?

Answer

Coffee contains caffeine molecules, which may be useful as quantum subsystems for a quantum computer because they contain two rings in a plane with many attached hydrogen atoms. The nuclear spin states of the H atoms attached to the rings can be used for information storage a la NMR. That is, a nuclear magnetic resonance (NMR) system is a collection of nuclear spin states in an external magnetic field that tend to align the spins. In the simplest ideal case at temperature T, the external magnetic field B is uniform and there are two spin states, up and down. Let’s say that B aligns most of the spins to the up state, with the ratio of down to up spins being determined by the exponential factor Exp(– μB/kT), where μ is the nuclear magnetic moment and k is the Boltzmann constant. An external radiofrequency pulse of the proper frequency v and energy hv = 2 μB can flip a down spin to an up spin for a stimulated absorption transition or can cause a stimulated emission of a photon by a spin flip from up to down.

Now for some coffee. The liquid contains about 1020 caffeine molecules. Even if we assume that all of them participate initially in bunches as coherent states of many quantum computers in the cup just before the calculation, most bunches will experience collisions during the calculation time of a nanosecond, say, and drop out from the collection of coherent states of the system. However, a significant number of bunches of coherent states may be participating still when the calculations are done, and these will provide a strong signal above the background noise. At least that’s the hope!