Abstract
Embedding a quantum state in a decoherence-free subspace (DFS) formed by multiple photons is one of the promising methods for robust entanglement distribution of photonic states over collective noisy channels. In practice, however, such a scheme suffers from a low efficiency proportional to transmittance of the channel to the power of the number of photons forming the DFS. The use of a counter-propagating coherent pulse can improve the efficiency to scale linearly in the channel transmission, but it achieves only protection against phase noises. Recently, it was theoretically proposed [Phys. Rev. A 87, 052325(2013)] that the protection against bit-flip noises can also be achieved if the channel has a reciprocal property. Here we experimentally demonstrate the proposed scheme to distribute polarization-entangled photon pairs against a general collective noise including the bit flip noise and the phase noise. We observed an efficient sharing rate scaling while keeping a high quality of the distributed entangled state. Furthermore, we show that the method is applicable not only to the entanglement distribution but also to the transmission of arbitrary polarization states of a single photon.
Highlights
Faithful and efficient distribution of photonic entangled states through noisy and lossy quantum channels is important for realizing various applications of quantum information processing, such as quantum key distribution[1, 2], quantum repeaters[3], and quantum computation between distant parties[4, 5]
When a two-photon decoherence-free subspace (DFS) is used for faithful quantum communication over a dephasing channel[6, 12], the transmission rate of quantum states is proportional to T2, where T is the transmittance of a single photon
We first review the protocol for sharing an entangled photon pair against general collective noise[20], in which it is assumed that the party is allowed to use two noisy channels
Summary
Faithful and efficient distribution of photonic entangled states through noisy and lossy quantum channels is important for realizing various applications of quantum information processing, such as quantum key distribution[1, 2], quantum repeaters[3], and quantum computation between distant parties[4, 5]. When we consider a random unitary (depolarizing) quantum channel, a four-photon DFS is needed to encode a signal photon state[6, 10, 18], which leads to the transmission rate in the order of T4 The inefficiency of such early DFS schemes has been resolved with an experimental demonstration in the case of entangled photon pairs distributed over a dephasing channel[19]. The key idea to improve the efficiency in the scheme is to prepare a reference single photon for the two-photon DFS from a coherent light pulse with an average photon number of (T −1) which propagates backwards along the quantum channel from the receiver to the sender of the signal photon This scheme has a non-zero failure probability of entanglement distribution in the case of T = 1, but the scaling of the achieved efficiency of sharing entanglement is proportional to T instead of T2. We show that our method is applicable to the distribution of any single-photon quantum state with the use of the quantum parity check[21]
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