Quantum repeater based on cavity QED evolutions and coherent light

Abstract

In the framework of cavity QED, we propose a quantum repeater scheme that uses coherent light and chains of atoms coupled to optical cavities. In contrast to conventional repeater schemes, we avoid the usage of two-qubit quantum logical gates by exploiting solely the cavity QED evolution. In our previous paper [D. Gonta and P. van Loock: Phys. Rev. A 88, 052308 (2013)], we already proposed a quantum repeater in which the entanglement between two neighboring repeater nodes was distributed using controlled displacements of input coherent light, while the produced low-fidelity entangled pairs were purified using ancillary (fourpartite) entangled states. In this paper, the entanglement distribution is realized using a sequence of controlled phase shifts and displacements of input coherent light. Compared to previous coherent-state-based distribution schemes for two-qubit entanglement, the present scheme relies only upon a simple discrimination of two coherent states with opposite signs, which can be performed in a quantum mechanically optimal fashion via a beam splitter and two on-off detectors. The entanglement purification utilizes a scheme that avoids the usage of ancillary entangled resources. Our repeater scheme exhibits reasonable fidelities and repeater rates providing an attractive platform for long-distance quantum communication.

Hybrid quantum repeater based on resonant qubit-field interactions

“…This scheme has the advantage that a high repetition rate can be achieved mainly due to almost unit efficiencies of homodyne photodetection of coherent states, in contrast to low efficiencies of single-photon detectors. Furthermore, for this type of quantum repeater every logical two-qubit gate is realized with the help of qubit-field interactions within cavity quantum electrodynamics (QED) scenarios [15,16]. These proposals are based on far-off-resonant qubit-field interactions, which impose limitations on the orthogonality of the field states involved in postselective homodyne measurements, thus * Electronic address: zsolt.bernad@um.edu.mt affecting the fidelity of the entangled states.…”