  Quantum computing has seen tremendous progress in the past years. Due to the
implementation complexity and cost, the future path of quantum computation is
strongly believed to delegate computational tasks to powerful quantum servers
on cloud. Universal blind quantum computing (UBQC) provides the protocol for
the secure delegation of arbitrary quantum computations, and it has received
significant attention. However, a great challenge in UBQC is how to transmit
quantum state over long distance securely and reliably. Here, we solve this
challenge by proposing and demonstrating a resource-efficient remote blind
qubit preparation (RBQP) protocol with weak coherent pulses for the client to
produce, using a compact and low-cost laser. We demonstrate the protocol in
field, experimentally verifying the protocol over 100-km fiber. Our experiment
uses a quantum teleportation setup in telecom wavelength and generates $1000$
secure qubits with an average fidelity of $(86.9\pm1.5)\%$, which exceeds the
quantum no-cloning fidelity of equatorial qubit states. The results prove the
feasibility of UBQC over long distances, and thus serving as a key milestone
towards secure cloud quantum computing.
