Causal nonseparability is the property underlying quantum processes incompatible with a definite causal order. So far it has remained a central open question as to whether any process with a clear physical realisation can violate a causal inequality, so that its causal nonseparability can be certified in a device-independent way, as originally conceived. Here we present a method solely based on the observed correlations, which certifies the causal nonseparability of all the processes that can induce a causally nonseparable distributed measurement in a scenario with trusted quantum input states, as defined in [Dourdent et al., Phys. Rev. Lett. 129, 090402 (2022)]. This notably includes the celebrated quantum switch. This device-independent certification is achieved by introducing a network of untrusted operations, allowing one to self-test the quantum inputs on which the effective distributed measurement induced by the process is performed.

中文翻译：

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因果不可分性认证与网络设备无关


因果不可分性是量子过程与确定的因果顺序不相容的属性。到目前为止，任何具有明确物理实现的过程是否可以违反因果不等式，从而可以像最初设想的那样，以独立于设备的方式证明其因果不可分性，这仍然是一个核心的悬而未决的问题。在这里，我们提出了一种仅基于观察到的相关性的方法，该方法证明了在具有可信量子输入状态的场景中可以诱导因果不可分分布式测量的所有过程的因果不可分性，如 [Dourdent et al.， Phys. Rev. Lett. 129， 090402 （2022）] 所定义]。这尤其包括著名的量子开关。这种独立于设备的认证是通过引入不受信任的操作网络来实现的，允许人们自测试量子输入，在该输入上执行由过程引起的有效分布式测量。