Farkas Máté, Balanzó-Juandó Maria, Łukanowski Karol, Kołodyński Jan, Acín Antonio
ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Spain.
Centre for Quantum Optical Technologies, Centre of New Technologies, University of Warsaw, Banacha 2c, 02-097 Warszawa, Poland.
Phys Rev Lett. 2021 Jul 30;127(5):050503. doi: 10.1103/PhysRevLett.127.050503.
Device-independent quantum key distribution is a secure quantum cryptographic paradigm that allows two honest users to establish a secret key, while putting minimal trust in their devices. Most of the existing protocols have the following structure: first, a bipartite nonlocal quantum state is distributed between the honest users, who perform local projective measurements to establish nonlocal correlations. Then, they announce the implemented measurements and extract a secure key by postprocessing their measurement outcomes. We show that no protocol of this form allows for establishing a secret key when implemented on any correlation obtained by measuring local projective measurements on certain entangled nonlocal states, namely, on a range of entangled two-qubit Werner states. To prove this result, we introduce a technique for upper bounding the asymptotic key rate of device-independent quantum key distribution protocols, based on a simple eavesdropping attack. Our results imply that either different reconciliation techniques are needed for device-independent quantum key distribution in the large-noise regime, or Bell nonlocality is not sufficient for this task.
与设备无关的量子密钥分发是一种安全的量子密码范例，它允许两个诚实的用户建立一个秘密密钥，同时对他们的设备信任度降至最低。大多数现有协议具有以下结构：首先，在诚实用户之间分发一个两方非局域量子态，用户进行局部投影测量以建立非局域关联。然后，他们公布所执行的测量，并通过对测量结果进行后处理来提取一个安全密钥。我们表明，当在通过对某些纠缠非局域态（即一系列纠缠的两量子比特维纳态）进行局部投影测量所获得的任何关联上实现时，这种形式的协议都不允许建立秘密密钥。为了证明这一结果，我们基于一种简单的窃听攻击，引入了一种用于限制与设备无关的量子密钥分发协议渐近密钥率上限的技术。我们的结果意味着，要么在大噪声 regime 中与设备无关的量子密钥分发需要不同的协调技术，要么贝尔非局域性对于此任务是不够的。
