# Map problem to quantum circuits and operators

The "map problem to quantum circuits and operators" step of a Qiskit pattern describes how a user starts with a classical problem and figures out how to map it to a quantum computer.

For example, in applications such as chemistry and quantum simulation, this step generally involves constructing a quantum circuit representing the Hamiltonian you are attempting to solve. During this step, for certain problems, it might also be desirable to specify the mapping of the problem onto qubits in the heavy-hex (or gross) lattice of IBM® hardware from the outset if the structure of the problem lends itself to optimization earlier.

It is also worth considering at this point what the outcome of the particular algorithm will be
in preparation for the later execute step - for example, if the desired outcome involves
inferring correlation functions using Hadamard tests, you might prepare to use `Sampler`

, whereas
specifying observables would use the `Estimator`

and could provide many error mitigation options.

The output of this step in a Qiskit pattern is normally a collection of circuits or quantum operators.

## Guides for mapping problems to quantum circuits and operators

### Build circuits with the Qiskit SDK

- Circuit library
- Construct circuits
- Visualize circuits
- Classical feedforward and control flow
- Synthesize unitary operators
- Bit-ordering in the Qiskit SDK
- Save circuits to disk

### Build operators with the Qiskit SDK

### Other circuit building tools

- Pulse schedules
- OpenQASM