Quantum tokens

An agency system comprising:

• a hardware device that generates or receives, at a first space-time point, a plurality of random quantum states, each of the quantum states chosen from a set of non-orthogonal quantum states;
• a measurement apparatus that applies a pre-determined measurement, from a plurality of possible pre-determined measurements, to the quantum states in order to obtain a token comprising a sequence of classical measurement outcomes, wherein the sequence of classical measurement outcomes is valid at a single space-time point;
• and
• a communications system that sends the token to a second agency system at a second space-time point in the causal future of the first space-time point, wherein the second agency system verifies whether the token corresponds to a statistically plausible result for the pre-determined measurement applied to the plurality of quantum states, before allowing access to a resource.