Dipartimento di Fisica dell'Università La Sapienza, Roma 00185, Italy.
Phys Rev Lett. 2010 Aug 13;105(7):073602. doi: 10.1103/PhysRevLett.105.073602.
Optimal quantum cloning is the process of making one or more copies of an arbitrary unknown input quantum state with the highest possible fidelity. All reported demonstrations of quantum cloning have so far been limited to copying two-dimensional quantum states, or qubits. We report the experimental realization of the optimal quantum cloning of four-dimensional quantum states, or ququarts, encoded in the polarization and orbital angular momentum degrees of freedom of photons. Our procedure, based on the symmetrization method, is also shown to be generally applicable to quantum states of arbitrarily high dimension-or qudits-and to be scalable to an arbitrary number of copies, in all cases remaining optimal. Furthermore, we report the bosonic coalescence of two single-particle entangled states.
最优量子克隆是指用最高保真度复制一个或多个任意未知输入量子态的过程。迄今为止，所有报道的量子克隆实验都仅限于复制二维量子态，即量子比特。我们报告了在光子的偏振和轨道角动量自由度中编码的四维量子态，即 ququarts 的最优量子克隆的实验实现。我们的基于对称化方法的方案也被证明在所有情况下都普遍适用于任意高维的量子态，即 qudits，并且可以扩展到任意数量的副本，并且始终保持最优。此外，我们报告了两个单粒子纠缠态的玻色凝聚。
