Quantum PUF for Security and Trust in Quantum Computing

Quantum computing is a promising paradigm to solve computationally intractable problems. Various companies such as, IBM, Rigetti and D-Wave offer quantum computers using a cloud-based platform that possess several interesting features namely, (i) quantum hardware with various number of qubits and coupling maps exist at the cloud end that offer different computing capabilities; (ii) multiple hardware with identical coupling maps exist in the suite; (iii) coupling map of larger hardware with more number of qubits can fit the coupling map of many smaller hardware; (iv) the quality of each of the hardware is distinct; (v) user cannot validate the origination of the result obtained from a quantum hardware. In other words, the user relies on the scheduler of the cloud provider to allocate the requested hardware; (vi) the queue of quantum programs at the cloud end is typically long and maximizing the throughput, which is the key to reducing costs and helping the scientific community in their explorations. The above factors motivate a new threat model with following possibilities: (a) in future, less-trustworthy quantum computers from 3rd parties can allocate poor quality hardware to save on cost or towards satisfying their falsely-advertised qubit or quantum hardware specifications; (b) the workload scheduling algorithm could have a bug or malicious code segment which will try to maximize throughput at the cost of allocation to poor fidelity hardware. Such bugs are possible for trustworthy providers; (c) a rogue employee in trusted cloud vendor could try to sabotage the vendor's reputation by degrading the user compute fidelity just by tampering with the scheduling algorithm or rerouting the program; (d) a rogue employee can steal information by redirecting the programs to a 3rd party quantum hardware where they have full control. If the allocated hardware is inferior in quality, the user will suffer from poor quality result or longer convergence time. We propose two flavors of a Quantum Physically Unclonable Function (QuPUF) to address this issue-one based on superposition and another based on decoherence. Our experiments on real quantum hardware reveal that temporal variations in qubit quality can degrade the quality of the proposed QuPUF. We add a parametric rotation to the QuPUF for stability. Experiments on real IBM quantum hardware show that the proposed QuPUF can achieve inter-die Hamming Distance (HD) of 55% and intra-HD as low as 4%, as compared to ideal cases of 50% and 0% respectively. The proposed QuPUFs can also be used as a standalone solution for any other application.