Paper 1, Section I, Introduce the 2 -qubit states
where and are the standard qubit Pauli operations and .
(a) For any 1-qubit state show that the 3 -qubit state of system can be expressed as
where the 1 -qubit states are uniquely determined. Show that .
(b) In addition to you may now assume that . Alice and Bob are separated distantly in space and share a state with and labelling qubits held by Alice and Bob respectively. Alice also has a qubit in state whose identity is unknown to her. Using the results of part (a) show how she can transfer the state of to Bob using only local operations and classical communication, i.e. the sending of quantum states across space is not allowed.
(c) Suppose that in part (b), while sharing the state, Alice and Bob are also unable to engage in any classical communication, i.e. they are able only to perform local operations. Can Alice now, perhaps by a modified process, transfer the state of to Bob? Give a reason for your answer.