Variational Quantum Eigensolver
Roughly, these are the steps of a VQE iteration.
- First, make a guess, also known as an ansatz, for the trial solution to the ground state of the quantum system. This guess can be anything, but the better it is, the better the performance. New methods focus on improving how to make more clever guesses on classical computers.
- The guess is parameterized and then used to construct the inputs for the quantum algorithms. The quantum computer then calculates components of the energy corresponding to this trial.
- These energy components are then sent to the classical computer. It uses clever techniques to use the parameters to "wiggle" the state and come up with a new guess for the trial ground state. There is a lot of fruitful research also on clever wiggle methods.
As this process goes on, each iteration should start to approach the correct solution. In our VQE example, this looks like this:
VQE has applications beyond chemistry, and is a great place to start to squeeze more power out of today's quantum computers.
You can read more about how to use Qiskit Runtime at Strangeworks here.