Knips Lukas, Schwemmer Christian, Klein Nico, Wieśniak Marcin, Weinfurter Harald
Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany.
Fakultät für Physik, Ludwig-Maximilians-Universität, D-80797 München, Germany.
Phys Rev Lett. 2016 Nov 18;117(21):210504. doi: 10.1103/PhysRevLett.117.210504.
Certifying entanglement of a multipartite state is generally considered a demanding task. Since an N qubit state is parametrized by 4^{N}-1 real numbers, one might naively expect that the measurement effort of generic entanglement detection also scales exponentially with N. Here, we introduce a general scheme to construct efficient witnesses requiring a constant number of measurements independent of the number of qubits for states like, e.g., Greenberger-Horne-Zeilinger states, cluster states, and Dicke states. For four qubits, we apply this novel method to experimental realizations of the aforementioned states and prove genuine four-partite entanglement with two measurement settings only.
验证多体状态的纠缠通常被认为是一项艰巨的任务。由于一个N量子比特状态由4^N - 1个实数参数化，人们可能会天真地期望，一般纠缠检测的测量工作量也会随N呈指数增长。在这里，我们引入一种通用方案，来构建高效的判据，对于诸如格林伯格-霍恩-泽林格态、簇态和迪克态等状态，所需的测量次数为常数，与量子比特的数量无关。对于四个量子比特，我们将这种新方法应用于上述状态的实验实现，并仅通过两种测量设置就证明了真正的四体纠缠。
