Abstract
We describe a method to detect twin-beam multiphoton entanglement based on a beam splitter and weak nonlinearities. For the twin-beam four-photon entanglement, we explore a symmetry detector. It works not only for collecting two-pair entangled states directly from the spontaneous parametric down-conversion process, but also for generating them by cascading these symmetry detectors. Surprisingly, by calculating the iterative coefficient and the success probability we show that with a few iterations the desired two-pair can be obtained from a class of four-photon entangled states. We then generalize the symmetry detector to n-pair emissions and show that it is capable of determining the number of the pairs emitted indistinguishably from the spontaneous parametric down-conversion source, which may contribute to explore multipair entanglement with a large number of photons.
Highlights
Since optical quantum systems provide some natural advantages, they are prominent candidates for quantum information processing[1,2,3]
We first focus on the twin-beam four-photon entangled states and design a quantum circuit of symmetry detector to evolve them by using a beam splitter (BS) and weak nonlinearities
Symmetry detector based on beam splitter and weak nonlinearities
Summary
Symmetry detector based on beam splitter and weak nonlinearities. Throughout the text, for simplicity we write are m horizontally p|mol,anr;izre, ds〉pahsoatnonasbbarnedvinatvioerntifcoarllsytapteo|lmar〉iazHed⊗ph|no〉taoVn⊗s in|r〉sbpHat⊗ial|ms〉boVdwe haicahndmaelasnostthheartetahreerer horizontally and s vertically polarized photons in spatial mode b. If there are n photons in the signal mode, it yields nθ in the probe mode, where θ = χt is a phase shift on the coherent probe beam induced by the interaction via Kerr media and t represents the interaction time. It is the twin-beam entangled state emitted by the SPDC source with the duration of the pump pulse is much shorter than the coherence time of the photons, and we here refer to this pair of the indistinguishable four-photon entangled states as two-pair, for simplicity For this two-pair, one can immediately obtain the result that the output state is the same as the input. When the photons passing through the 50:50 BS, the transformation between the incoming modes (a1 and b1) and the outgoing modes (a2 and b2) is (a1†Hb1†V a1†V b1†H)n
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