Noise Propagation and Effective Channels in Encrypted Quantum Cloning

arXiv:2610.38240v1 Announce Type: new Abstract: We investigate noise propagation in encrypted quantum cloning by formulating the protocol in terms of effective recovery channels. For local single-qubit completely positive trace-preserving noise, a Pauli-basis expansion of the Kraus operators reveals a strong dependence on the location of the physical channel. Noise on an auxiliary signal qubit leaves the reduced recovered state unchanged, whereas noise on an auxiliary key qubit induces a Pauli-diagonal effective channel on the recovered qubit. For the core qubits, the error propagation additionally depends on the parity of the number of entangled pairs.