Qiskit is an open-source quantum computing software development kit (SDK) that allows users to build and run quantum programs on real quantum hardware as well as on simulators. The Qiskit simulator is one of the key components of the Qiskit SDK, and it has a rich history of development and evolution.

The first version of the Qiskit simulator was introduced in 2017 when IBM released the first version of Qiskit. At that time, the simulator was a simple Python library that provided a way to simulate quantum circuits on classical computers. It was based on the matrix product state (MPS) representation of quantum states and used a numerical method called time-evolving block decimation (TEBD) to simulate the evolution of quantum circuits.

Over time, the Qiskit simulator has evolved significantly, with many new features and improvements added to it. For example, in 2018, IBM introduced the ability to simulate noisy quantum circuits using a technique called quantum process tomography (QPT). This made it possible to simulate more realistic quantum circuits that take into account the effects of noise and errors in real quantum hardware.

In 2019, IBM introduced the Aer quantum simulator, which is a high-performance simulator that can simulate large-scale quantum circuits with millions of qubits and gates. The Aer simulator uses a combination of classical simulation techniques and quantum-inspired methods to achieve high performance.

More recently, in 2020, IBM introduced the Qiskit Runtime, which allows users to run quantum circuits on IBM's cloud-based quantum hardware using the Qiskit simulator as a backend. This makes it possible to test and optimize quantum circuits before running them on real hardware, thereby reducing the time and cost associated with running experiments on real quantum devices.

Overall, the Qiskit simulator has come a long way since its inception, and it continues to evolve and improve as quantum computing technology advances.