Systematic Approaches for Precise and Approximate Quantum State Runtime Assertion

With the rapid growth of quantum computing technology, programmers need new tools for debugging quantum programs. Recent works show that assertions are a promising way for debugging quantum programs. However, there are two main drawbacks with the existing schemes. First, the existing schemes, including both statistical and dynamic assertions are only capable of asserting limited types of states, namely classical, superposition, and specific entanglement states. Second, the use cases of these assertions are limited, since the programmer has to know the exact/precise state to assert.In this work, we propose two systematic approaches for dynamic quantum state assertion and they can assert a much broader range of quantum states including both pure states and mixed states. We also introduce the idea of approximate quantum state assertion for the cases where the programmers only have limited knowledge of the quantum states. Approximate assertion is capable of checking membership in a set of states $\{|\psi\rangle,\ |\phi\rangle,\ldots\}$. While precise quantum state assertion can check a specific quantum state, approximate assertion enables a way to check whether the qubits of interest are in a super-set of some expected states, which is analogous to the well-known Bloom filter for membership checking in classical computing. Our experiments demonstrate that our systematic approaches can assert many more quantum states and can be used in various assertion locations for qubit state checking.