Oct 2023 - Sep 2024

Tobias Hartung, "Testing Quantum Computer Controllability via Dimensional Expressivity"




Quantum Devices are currently undergoing rapid development and many different physical architectures are studied as candidates for quantum computation. In contrast to classical computing however, the physical controls of a quantum device are less directly linked to the operations we wish to perform. That is, while on classical hardware we can build transistors that physically act as the gates (AND, OR, NOT, ...) we wish to implement, quantum devices are usually controlled through physical effects on qubits, such as, electro-magnetic fields applied to qubits or using the Josephson effect for superconducting qubits. Additionally, many quantum devices are subject to non-trivial dynamics of the quantum system itself. Hence, deciding whether a given set of controls is sufficient for quantum computation becomes a non-trivial question as well.

In this talk, I will discuss the notion of Dimensional Expressivity Analysisand how to use it for testing whether a quantum system is controllable and thus usable for quantum computation. Furthermore, this will enable us to identify whether there are redundant controls in the system. Time permitting, the approach also gives insight into best-approximation errors for systems that are not controllable, i.e., given a set of controls that is insufficient for universal quantum computing, how can we quantify the error introduced by this hardware?