Quantum Circuits for Imaginary Time Evolution

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• Chiara Leadbeater, University of Cambridge
• Wednesday 28 May 2025, 14:30-15:30
• Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry.

If you have a question about this talk, please contact Lisa Masters.

Accurate prediction of ground-state electronic energies is essential for understanding chemical reactivity, catalysis, and material properties. One of the most promising applications of quantum computers is the simulation of chemical systems. While imaginary time evolution (ITE) is widely used on classical hardware to obtain ground states, its implementation on quantum hardware is challenging due to its non-unitary nature.

Near-term approaches to this problem have relied on heuristics, compromising their accuracy. As we enter the early fault-tolerant era of quantum computing, there is growing interest in the development of more natively quantum algorithms. Since it is not possible to implement a non-unitary gate deterministically, we resort to probabilistic ITE (PITE) algorithms. These embed the ITE operator inside a larger unitary matrix, which is accessed via post-selection of “successful” mid-circuit measurements. In our previous work, we introduced a novel PITE algorithm that yields shorter circuits and is easier to implement than existing PITE approaches [1].

This talk will provide an introduction to quantum circuits, before focusing on the challenges associated with PITE algorithms. In particular, we will discuss the feasibility of implementing an Amplitude Amplification routine [2], as well as a new “boosting” procedure, which uses successive reflection operations to boost to lower energy states [3].

[1] C. Leadbeater, N. Fitzpatrick, D. M. Ramo, and A. J. W. Thom, Quantum Sci. Technol. 9, 045007 (2024). [2] H. Nishi, T. Kosugi, Y. Nishiya, and Y.-i. Matsushita, Phys. Rev. B 110 , 174302 (2024). [3] B. C. B. Symons, D. Manawadu, D. Galvin, and S. Mensa, Phys. Rev. Res. 6, L022041 (2024).

This talk is part of the Theory - Chemistry Research Interest Group series.

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