However there's also a minute possibility that any other message will appear in the clear. Practice proving that this is unconditionally secure without looking at the proof. You need as much key as plaintext. We need truly random keys - can't use an algorithm since it won't give us true independence. Something that doesn't give us the randomness we want is a computer random number generator, which takes a small number of random bits and produces a uniform distribution of random bits that will fool randomness statistical test.
Key management becomes a problem.
Properties of solid state electronic devices to report back quantum state. E.G. a zener diode is over-driven and reveals and quantum state. Or get a radioactive source and make measurements of the material. Must be monitored very carefully to be sure you're looking at the effect you think you're measuring. During the Cold War, Soviets communicated most sensitive data encrypted with one- time pads.