Quantum computers are currently being researched intensively worldwide and some companies are already providing “quantum computers in the cloud”. This means that one can already take advantage of quantum computers by running one’s data and analysis on appropriately online quantum hardware.

Intensive research is being conducted at the Know Center to make such evaluations on quantum computers secure and to protect data and algorithms here as well. In initial work, researchers at the Know Center have exploited the “noise” of qubits, the basic building blocks of a quantum computer, to determine what was previously computed on the quantum computer.

Interfering factors such as cosmic rays, the physical environment of the quantum computer, and even other qubits, can create “noise” within the quantum circuits. This can affect results of a calculation and thus lead to errors. Current research therefore focuses heavily on minimizing this noise.

Inspired by the classic hacking method of side-channel attacks – accessing indirect information in the computer system rather than attacking the system directly – the idea of performing a “prime-and-probe” attack emerged. This type of attack attempts to put the system in a certain state, which then allows indirect analysis. All computations on IBM’s public cloud quantum computing platform end up in a waiting list and are processed in order on the respective quantum computer.

Researchers at the Know Center exploited the fact that the noise of the qubits does not change randomly and were able to reconstruct which computation was performed by cleverly determining and manipulating the state of the quantum computer immediately before and after a foreign computation.

The results point to a potential security vulnerability in cloud-based quantum computing that should accordingly be explored further.

The scientists’ experiment has since attracted the attention of research groups in Europe and the U.S. that are exploring noise mitigation to secure cloud-based quantum computing systems and the optimization of quantum algorithms. A loose collaboration with researchers at Yale University is also expected to further explore related topics together.