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Deterministic quantum teleportation of photonic quantum bits by a hybrid technique

Quantum teleportation allows for the transfer of arbitrary, in principle, unknown quantum states from a sender to a spatially distant receiver, who share an entangled state and can communicate classically. It is the essence of many sophisticated protocols for quantum communication and computation. In order to realize flying qubits in these schemes, photons are an optimal choice, however, teleporting a photonic qubit has been limited due to experimental inefficiencies and restrictions. Major disadvantages have been the fundamentally probabilistic nature of linear-optics Bell measurements as well as the need for either destroying the teleported qubit or attenuating the input qubit when the detectors do not resolve photon numbers. Here we experimentally realize fully deterministic, unconditional quantum teleportation of photonic qubits. The key element is to make use of a "hybrid" technique: continuous-variable (CV) teleportation of a discrete-variable, photonic qubit. By optimally tuning the receiver's feedforward gain, the CV teleporter acts as a pure loss channel, while the input dual-rail encoded qubit, based on a single photon, represents a quantum error detection code against amplitude damping and hence remains completely intact for most teleportation events. This allows for a faithful qubit transfer even with imperfect CV entangled states: the overall transfer fidelities range from 0.79 to 0.82 for four distinct qubits, all of them exceeding the classical limit of teleportation. Furthermore, even for a relatively low level of the entanglement, qubits are teleported much more efficiently than in previous experiments, albeit post-selectively (taking into account only the qubit subspaces), with a fidelity comparable to the previously reported values.