Gentle quantum leakage is proposed as a measure of information leakage to arbitrary eavesdroppers that aim to avoid detection. Gentle (also sometimes referred to as weak or non-demolition) measurements are used to encode the desire of the eavesdropper to evade detection. The gentle quantum leakage meets important axioms proposed for measures of information leakage including positivity, independence, and unitary invariance. Global depolarizing noise, an important family of physical noise in quantum devices, is shown to reduce gentle quantum leakage (and hence can be used as a mechanism to ensure privacy or security). A lower bound for the gentle quantum leakage based on asymmetric approximate cloning is presented. This lower bound relates information leakage to mutual incompatibility of quantum states. A numerical example, based on the encoding in the celebrated BB84 quantum key distribution algorithm, is used to demonstrate the results.

翻译：温和量子泄露被提出作为针对任意试图逃避检测的窃听者的信息泄露度量。温和测量（有时也称为弱测量或非破坏性测量）被用于编码窃听者规避检测的意图。该度量满足信息泄露度量所提出的重要公理，包括非负性、独立性和幺正不变性。全局退极化噪声——量子器件中一类重要的物理噪声——被证明能降低温和量子泄露（因此可作为确保隐私或安全的机制）。基于非对称近似量子克隆的温和量子泄露下界被提出。该下界将信息泄露与量子态间的互不兼容性相关联。采用著名BB84量子密钥分发算法的编码作为数值示例，对所获结果进行了验证。