Abstract
Enabling the sharing of quantum computers among different users requires a secure reset operation that can reset the state of a qubit to ground state |0$>$ and prevent leakage of the state to a post-reset circuit. This work highlights that the existing reset operations available in superconducting qubit NISQ quantum computers are not fully secure. In particular, this work demonstrates for the first time a new type of higher-energy state attack. Although NISQ quantum computers are typically abstracted as working with only energy states |0$>$ and |1$>$, this work shows that it is possible for unprivileged users to set the qubit state to |2 or |3$>$. By breaking the abstraction of a two-level system, the new higher-energy state attack can be deployed to affect the operation of circuits or for covert communication between circuits. This work shows that common reset protocols are ineffective in resetting a qubit from a higher-energy state. To provide a defense, this work proposes a new Cascading Secure Reset (CSR) operation. CSR, without hardware modifications, is able to efficiently and reliably reset higher-energy states back to |0$>$. CSR achieves a reduction in |3$>$ -initialized state leakage channel capacity by between 1 and 2 orders of magnitude, and does so with a 25x speedup compared with the default decoherence reset.
Chuanqi Xu
Ph.D. Student
I am a PhD student at Yale University, and my research interests lie in quantum computing and computer security. I am currently working on quantum computer security, where I design attack and defense mechanisms on quantum computers and quantum cloud providers. I am also working on RTL design (Verilog) targeting FPGAs, where I implement Post-Quantum Cryptography (PQC) schemes that are secure under both classical and quantum computer attacks.