Forward Quantum Annealing: one solution after another.
Hello,
In the reverse annealing process, I read that the process per default always starts from the same initial state (given by the user) or from the last solution obtained if the option is activated. This made me wonder what is going on for the forward quantum annealing: does each anneal always starts from the same superposition state, or does it start from the previous state (solution) that the QPU read? In that last case, I understand that after each reading/sampling, so after the particles wave function had collapsed, the QPU wait a little bit to reinitialize the system from the last solution obtained. More generally: where I can find info about Quantum Annealing made by D-Wave especially focusing on the step going from one solution to another?
Thanks you very much.
Comments
Hi Samuel,
The D-Wave system starts each anneal with the qubits being in a superposition state. During the annealing process the couplers and biases are introduced and by the end of the anneal each qubit is in a classical state that represents the minimum energy state of the problem. If there are multiple cycles, the processor is returned to the superposition state (i.e. the ground state of the initial Hamiltonian) during the 'delay time' phase. (see Fig 104)
Unlike the annealing process where qubits always start in a superposition state, the reverse anneal feature requires the user to select a classical starting position (initial_state parameter) and if there are multiple cycles the reinitialize_state solver parameter determines if the qubits are reset to their initial_state before each cycle, or if they use the final state from the previous cycle.
I recommend the following documents for more information about the annealing process:
https://docs.dwavesys.com/docs/latest/c_gs_2.html#what-is-quantum-annealing
https://docs.dwavesys.com/docs/latest/c_qpu_timing.html#breakdown-of-qpu-access-time
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