  The success of quantum circuits in providing reliable outcomes for a given
problem depends on the gate count and depth in near-term noisy quantum
computers. Quantum circuit compilers that decompose high-level gates to native
gates of the hardware and optimize the circuit play a key role in quantum
computing. However, the quality and time complexity of the optimization process
can vary significantly especially for practically relevant large-scale quantum
circuits. As a result, third-party (often less-trusted/untrusted) compilers
have emerged, claiming to provide better and faster optimization of complex
quantum circuits than so-called trusted compilers. However, untrusted compilers
can pose severe security risks, such as the theft of sensitive intellectual
property (IP) embedded within the quantum circuit. We propose an obfuscation
technique for quantum circuits using randomized reversible gates to protect
them from such attacks during compilation. The idea is to insert a small random
circuit into the original circuit and send it to the untrusted compiler. Since
the circuit function is corrupted, the adversary may get incorrect IP. However,
the user may also get incorrect output post-compilation. To circumvent this
issue, we concatenate the inverse of the random circuit in the compiled circuit
to recover the original functionality. We demonstrate the practicality of our
method by conducting exhaustive experiments on a set of benchmark circuits and
measuring the quality of obfuscation by calculating the Total Variation
Distance (TVD) metric. Our method achieves TVD of up to 1.92 and performs at
least 2X better than a previously reported obfuscation method. We also propose
a novel adversarial reverse engineering (RE) approach and show that the
proposed obfuscation is resilient against RE attacks. The proposed technique
introduces minimal degradation in fidelity (~1% to ~3% on average).
