polarization photons
One theoretically surefire way for Alice to cheat is to utilize the Einstein-Podolsky-Rosen (EPR) paradox. Two photons in an EPR pair are anticorrelated; that is, they will always be found to have opposite polarizations, provided that they are measured in the same basis. Alice could generate a string of EPR pairs, sending one photon per pair to Bob and storing the other herself. When Bob states his guess, she could measure her EPR pair photons in the opposite basis and obtain a perfect correlation to Bob's opposite table. Bob would never know she cheated. However, this requires capabilities that quantum technology currently does not possess, making it impossible to do in practice. To successfully execute this, Alice would need to be able to store all the photons for a significant amount of time as well as measure them with near perfect efficiency. This is because any photon lost in storage or in measurement would result in a hole in her string that she would have to fill by guessing. The more guesses she has to make, the more she risks detection by Bob for cheating.
