The Variational Quantum Eigensolver (VQE) is a mixed quantum-classical tool used in nuclear physics to determine the lowest possible energy state of a composite system.

Per the IBM Quantum Platform, the VQE consists of four central components:
1. The Hamiltonian Operator represents the total energy in the system (this is what we want to optimize)
2. The ansatz is a family of quantum circuits that, through the variation of gate parameters such as rotation angles, allows the VQE to approximate the ground state energy
3. An estimator allows the VQE to calculate the cost function (expectation value) of a system
4. A classical optimizer provides a framework algorithm that minimizes the cost function through gradient-based methods

This summer, I did a project on optimizing simulations of carbon isotopes on quantum computers. It centered around determining the VQE’s efficacy when exposed to differing conditions (for example, the VQE’s performance in low-noise environments compared to high-noise environments). It was a very fun project and I really enjoyed working on it! We found that the VQE tended to converge to a value not close to the true ground state energy of the system in the presence of noisy conditions; overall, however, the findings of my study indicated that the VQE can feasibly be utilized in larger-scale nuclear simulations! In order to mitigate adverse effects generated by noise, we hope to implement a noise-resilient technique that will help improve the accuracy of the VQE’s optimization of the cost function.

We also considered the initial potential depth the system was exposed to – however, there was no clear effect on the VQE’s convergence, although we did find that the nucleus became less strongly-bound when exposed to larger potential depths.

I strongly encourage those interested to seek out opportunities for research in the quantum field! It was truly a fun experience for me to perform work based on my own interests, and I hope that the same holds true for others.