Abstract

Quantum money was one of the first inventions in quantum information technology. The idea is to make money tokens by including some stored quantum states, whose description the bank knows but users do not. Intuitively, these tokens should be unforgeable because the quantum no-cloning theorem tells us that there is no possible way of constructing a device that will duplicate unknown quantum states. As I will explain, though, proving this intuition takes rather more work. Quantum money is not currently practical, because we have no long-term quantum memories. However, I will describe a recently proposed way of emulating its advantages without quantum memories, and an experimental demonstration. Interestingly, this involves re-examining what the advantages of quantum money actually are, which requires re-thinking the role of money in space and time.