Mi-Ying Huang

Program obfuscation aims to hide a program’s internal structure while preserving its functionality. In the quantum world, whether one can obfuscate general quantum circuits has remained a central open question. Previous works achieved obfuscation only for highly restricted classes of quantum programs, leaving a significant gap toward obfuscation of full quantum computation . We close this gap through a sequence of results. We first show how to obfuscate unitary quantum programs with quantum inputs and outputs in the classical oracle model—removing the earlier pseudo-deterministic restriction and handling genuinely quantum behavior. We then build on this foundation to obtain the first quantum ideal obfuscation scheme for arbitrary quantum circuits, encompassing general completely positive trace-preserving (CPTP) maps. Our constructions rely solely on post-quantum one-way functions in the classical oracle model and develop new techniques, including functional quantum authentication and subspace-preserving pseudorandom unitaries. Together, these results resolve a series of open problems and establish the first obfuscation scheme for general quantum circuits with quantum inputs and outputs in the classical oracle model.

Program obfuscation aims to hide the inner workings of a program while preserving its functionality. In the quantum setting, recent works have obtained obfuscation schemes for specialized classes of quantum circuits. For instance, Bartusek, Brakerski, and Vaikuntanathan (STOC 2024) constructed a quantum state obfuscation scheme, which supports the obfuscation of quantum programs represented as quantum states for pseudo-deterministic quantum programs with classical inputs and outputs in the classical oracle model. In this work, we improve upon existing results by constructing the first quantum state obfuscation scheme for unitary (or approximately unitary) quantum programs supporting quantum inputs and outputs in the classical oracle model. At the core of our obfuscation scheme are two novel ingredients: a functional quantum authentication scheme that allows key holders to learn specific functions of the authenticated quantum state with simulation-based security, and a compiler that represents an arbitrary quantum circuit as a projective linear-plus-measurement quantum program described by a sequence of non-adaptive Clifford gates interleaved with adaptive and compatible measurements.