  The recently proposed Universal Blind Quantum Computation (UBQC) protocol
allows a client to perform an arbitrary quantum computation on a remote server
such that perfect privacy is guaranteed if the client is capable of producing
random separable single qubit states. While from a theoretical point of view,
this arguably constitutes the lowest possible quantum requirement, from a
pragmatic point of view, generation of random single qubits which can be sent
along long distances without loss is quite challenging and can never be
achieved perfectly.
  In analogy to the concept of approximate security developed for other
cryptographic protocols, we introduce here the concept of approximate blindness
for UBQC, allowing us to characterize the robustness of the protocol to
possible imperfections.
  Following this, we present a remote blind single qubit preparation protocol,
by which a client with access to realistic quantum devices (such as coherent
laser light) can in a delegated fashion prepare quantum states arbitrarily
close to perfect random single qubit states. We finally prove that access to
coherent states is sufficient to efficiently achieve approximate blindness with
arbitrary small security parameter.
