Single-copy entanglement detection

One of the main challenges of quantum information is the reliable verification of quantum entanglement. The conventional detection schemes require repeated measurement on a large number of identically prepared systems. This is hard to achieve in practice when dealing with large-scale entangled quantum systems. In this letter we formulate verification as a decision procedure, i.e., entanglement is seen as the ability of quantum system to answer certain “yes-no questions”. We show that for a variety of large quantum states even a single copy suffices to detect entanglement with a high probability by using local measurements. For example, a single copy of a 16-qubit k-producible state or one copy of 24-qubit linear cluster state suffices to verify entanglement with more than 95% confidence. Our method is applicable to many important classes of states, such as cluster states or ground states of local Hamiltonians in general.Quantum correlations: resource-efficient entanglement detectionA single copy of a quantum system and local measurements are sufficient for high-probability entanglement detection. Conventional entanglement detection schemes require multiple copies of a given quantum state, which can be impractical or simply impossible—particularly for large states. Aleksandra Dimić (University of Belgrade) and Borivoje Dakić (Austrian Academy of Sciences & University of Vienna) have conceived a method for entanglement detection that requires only single copies of multi-partite quantum states. This is based on the success probability of a suitably designed experimental run, which is exponentially suppressed in the system size for separable states, but remains close to certainty for specific entangled ones. Hence, success or failure identifies the state as entangled or separable with high probability. This approach promises reliable entanglement detection at reduced resources need, making it useful for future applications based on large entangled states.