Quantum teleportation provides a disembodied way to transfer an unknown quantum state from one quantum system to another. However, all teleportation experiments to date are limited to cases where the target quantum system contains no prior quantum information. Here we propose a scheme for teleporting a quantum state to a quantum system with prior quantum information. By using an optical qubit-ququart entangling gate, we have experimentally demonstrated the new teleportation protocol -- teleporting a qubit to a photon preloaded with one qubit of quantum information. After the teleportation, the target photon contains two qubits of quantum information, one from the teleported qubit and the other from the pre-existing qubit. The teleportation fidelities range from $0.70$ to $0.92$, all above the classical limit of $2/3$. Our work sheds light on a new direction for quantum teleportation and demonstrates our ability to implement entangling operations beyond two-level quantum systems.
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