Frequency-multiplexing is an effective method to achieve resource-efficient superconducting qubit readout. Allowing multiple resonators to share a common feedline, the number of cables and passive components involved in the readout of a qubit can be drastically reduced. However, this improvement in scalability comes at the price of a crucial non-ideality -- an increased readout crosstalk. Prior works have targeted building better devices and discriminators to reduce its effects, as readout-crosstalk-induced qubit measurement errors are detrimental to the reliability of a quantum computer. However, in this work, we show that beyond the reliability of a system, readout crosstalk can introduce vulnerabilities in a system being shared among multiple users. These vulnerabilities are directly related to correlated errors due to readout crosstalk. These correlated errors can be exploited by nefarious attackers to predict the state of the victim qubits, resulting in information leakage.

翻译：频率复用是一种实现资源高效超导量子比特读出的有效方法。通过允许多个谐振器共享同一馈线，可大幅减少量子比特读出过程中涉及的线缆和无源元件数量。然而，这种可扩展性的提升是以关键非理想性为代价的——即读出串扰的增加。先前的研究致力于构建更优的器件和判别器以降低其影响，因为读出串扰导致的量子比特测量误差会损害量子计算机的可靠性。然而，在本工作中，我们表明：除系统可靠性之外，读出串扰还可能引入多用户共享系统中的漏洞。这些漏洞与读出串扰导致的关联误差直接相关。恶意攻击者可以利用这些关联误差来预测受害量子比特的状态，从而造成信息泄露。