Teleportation-based realization of an optical quantum two-qubit entangling gate

Abstract

In recent years, there has been heightened interest in quantum teleportation, which allows for the transfer of unknown quantum states over arbitrary distances. Quantum teleportation not only serves as an essential ingredient in long-distance quantum communication, but also provides enabling technologies for practical quantum computation. Of particular interest is the scheme proposed by D. Gottesman and I. L. Chuang [(1999) Nature 402:390-393], showing that quantum gates can be implemented by teleporting qubits with the help of some special entangled states. Therefore, the construction of a quantum computer can be simply based on some multiparticle entangled states, Bell-state measurements, and single-qubit operations. The feasibility of this scheme relaxes experimental constraints on realizing universal quantum computation. Using two different methods, we demonstrate the smallest nontrivial module in such a scheme-a teleportationbased quantum entangling gate for two different photonic qubits. One uses a high-fidelity six-photon interferometer to realize controlled-NOT gates, and the other uses four-photon hyperentanglement to realize controlled-Phase gates. The results clearly demonstrate the working principles and the entangling capability of the gates. Our experiment represents an important step toward the realization of practical quantum computers and could lead to many further applications in linear optics quantum information processing.I n 2001, Knill, Laflamme, and Milburn (KLM) showed that scalable and efficient quantum computation is possible by using linear optical elements, ancilla photons, and postselection (1). The KLM scheme is based on three principles. First, nondeterministic quantum computation is possible with linear optics. Second, universal quantum gates with the probability approaching one can be implemented based on teleportation (2), a process in which a qubit in an unknown state can be transferred to another qubit (3, 4). Third, the demanding resources can be reduced by quantum coding. The first principle has been demonstrated in many experiments. For example, various approaches for realizing photonic controlled-NOT (C-NOT) gates have been reported (5-11). Recently, a three-qubit Toffoli gate has also been carried out in a photonic architecture (12). Additionally, there have been many efforts aimed at reducing the resource requirements of the KLM protocol (13-16). Nevertheless, the teleportation-based two-qubit entangling gate, which plays an important role in the second principle of the KLM scheme, still remains an experimental challenge.Quantum teleportation is useful for quantum communication (17, 18) because it allows us to use entangled states as perfect quantum channels. The unique scheme proposed by Gottesman and Chuang (GC) in 1999 (2) opens the way for promising applications in realizing quantum computation (1,2,13,14,19). In the GC scheme, qubits are teleported through special gates by simply using multiparticle off-line entangled states, Bell-state measurements (BSM), and single...

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