Sentís Gael, Bagan Emilio, Calsamiglia John, Chiribella Giulio, Muñoz-Tapia Ramon
Departamento de Física Teórica e Historia de la Ciencia, Universidad del País Vasco UPV/EHU, E-48080 Bilbao, Spain.
Física Teòrica: Informació i Fenòmens Quàntics, Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain.
Phys Rev Lett. 2016 Oct 7;117(15):150502. doi: 10.1103/PhysRevLett.117.150502.
Sudden changes are ubiquitous in nature. Identifying them is crucial for a number of applications in biology, medicine, and social sciences. Here we take the problem of detecting sudden changes to the quantum domain. We consider a source that emits quantum particles in a default state, until a point where a mutation occurs that causes the source to switch to another state. The problem is then to find out where the change occurred. We determine the maximum probability of correctly identifying the change point, allowing for collective measurements on the whole sequence of particles emitted by the source. Then, we devise online strategies where the particles are measured individually and an answer is provided as soon as a new particle is received. We show that these online strategies substantially underperform the optimal quantum measurement, indicating that quantum sudden changes, although happening locally, are better detected globally.
自然界中突变无处不在。识别突变对于生物学、医学和社会科学中的许多应用至关重要。在此，我们将突变检测问题拓展到量子领域。我们考虑一个以默认状态发射量子粒子的源，直到发生突变使源切换到另一种状态。问题在于找出变化发生的位置。我们确定了正确识别变化点的最大概率，这允许对源发射的整个粒子序列进行集体测量。然后，我们设计了在线策略，即对粒子进行逐个测量，并在接收到新粒子时立即给出答案。我们表明，这些在线策略的性能远低于最优量子测量，这表明量子突变虽然局部发生，但从全局角度能更好地被检测到。
