The superposition principle is fundamental to quantum theory. Yet a recent no-go theorem has proved that quantum theory forbids superposition of unknown quantum states, even with nonzero probability. The implications of this result, however, remain poorly understood so far. In this Rapid Communication we show that the existence of a protocol that superposes two unknown pure states with nonzero probability (allowed to vary over input states) leads to the violation of other no-go theorems. In particular, such a protocol can be used to perform certain state discrimination and cloning tasks that are forbidden not only in quantum theory but in no-signaling theories as well.

中文翻译：

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不可能创建未知量子态的叠加

叠加原理是量子理论的基础。然而，最近的一个不做定理已经证明，量子理论即使在概率非零的情况下也禁止叠加未知的量子态。但是，到目前为止，对这一结果的含义仍知之甚少。在此快速通信中，我们证明了以非零概率（允许在输入状态上变化）叠加两个未知纯状态的协议的存在会导致违反其他非定理。特别地，这样的协议可以用于执行某些状态区分和克隆任务，这不仅在量子理论中而且在无信号理论中也被禁止。