We are pleased to announce a seminar by leading expert Dr Tobias Hartung (Northeastern University London) for the PQM discussion group on 18 Feb 2026:
On Convergence and Efficiency of Quantum Imaginary Time Evolution
Many current applications of quantum simulations are based on variational methods. These variational methods are commonly subject to effects that can prevent convergence to global solutions. While options to circumvent these obstacles exist, they generally come at the cost of efficiency.
In this talk, we will consider the quantum imaginary time evolution. We will show convergence guarantees for imaginary time evolution to the global optimum, and prove convergence rates as well as the absence of critical slowing down. This will allow us to obtain estimates on the evolution time required to reach fidelity thresholds. In particular, for combinatorial optimization problems we can conclude that success probability thresholds can be reached in linear evolution time with respect to system size in qubits and the inverse energy gap.
Furthermore, we will discuss the circuit compilation for quantum imaginary time evolution in detail. Considering bounded order systems with polynomial coefficient scaling in particular, we will show that the corresponding quantum circuits implementing imaginary time evolution can be compiled using polynomial resources in qubits, inverse energy gap, and approximation error bounds.