A decentralized online quantum cash system, called qBitcoin, is given. Researchers designed a system which has great benefits of quantization in the following sense.>A Firstly, quantum teleportation technology is used for coin transaction, which prevents an owner of a coin from keeping the original coin data after sending the coin to another. This was a main problem in systems using classical information and a blockchain was introduced to solve this issue. In qBitcoin, the double-spending problem never happens and its security is guaranteed theoretically by virtue of quantum information theory. Making a bock is time consuming and the system of qBitcoin is based on a quantum chain, instead of blocks. Therefore a payment can be completed much faster than Bitcoin. Moreover they employ quantum digital signature so that it naturally inherits properties of peer-to-peer (P2P) cash system as originally proposed in Bitcoin.
The novelty of qBitcoin compared to Bitcoin or other quantum money schemes can be summarized as follows.
1. Quantum teleportation is used to transmit a coin. This prevents from double spending in a simple way without help of a blockchain.
2. Quantum digital signature is used to verify transaction. This requires other participants to be involved in verifying signatures, hence it is compatible with P2P.
3. Transaction data is stored not in a block but in a point, hence transaction is immediately completed once if signature is verified. In other words, a blockchain is replaced by a quantum chain.