Cyclic Remote Implementation of Partially Unknown Quantum Operations

We present a novel scheme of Cyclic remote implementation of partially unknown quantum operations (CRIPUQO) via a six-qubit entangled state as the quantum channel. Alice can remotely apply a partially unknown quantum operation U_d (d = 0, 1) to Bob's qubit b, and Bob can remotely apply U_d to Charlie's site; meanwhile, Charlie can also remotely apply U_d to Alice's qubit c. It is pointed out that the CRIPUQO in the opposite direction can be perfectly achieved by changing the quantum channel. The scheme above is also generalized to systems having N observers, so that the CRIPUQO can be realized in quantum information networks with N observers in different directions by changing quantum channels.