# Overview

## Welcome to the Classiq Documentation¶

As quantum hardware progresses from dozens to thousands of qubits and beyond, it is no longer feasible to design and optimize circuits at the gate and building block levels alone.

The Classiq platform automates circuit synthesis from the high-level model to the gate-level solution and hardware execution, leaving the quantum algorithm developer free to model quantum circuits that can solve real-world problems.

Development teams use the Classiq platform to quickly and easily design, analyze, and optimize sophisticated quantum circuits. The software platform transforms high-level functional models into concrete quantum circuits optimized for the back-end of choice.

This platform will help you design quantum circuits with greater ease and speed than ever before.

## How Does Classiq Do It?¶

Quantum algorithm design (QAD) is the quantum version of computer-aided design (CAD). The Classiq QAD platform asks designers to describe the circuit functionality by creating a high-level circuit model. They write the model using a Quantum Description Language (QDL) with a textual or a Python (SDK) interface.

The Classiq synthesis engine ingests the model and uses advanced constrained optimization solvers to choose the optimal circuit (or circuits) from amongst billions of possible options. The synthesis engine aims to find a circuit that matches a set of constraints and rules that the designer defines, as well as general rules embedded in the platform—that the designer can override. The Classiq platform implicitly optimizes a complex design process, including qubit allocation, computation strategies, auxiliary qubit reuse, global resource management, and more.

The Classiq platform can output the synthesized circuits in any common universal gate-level format (OpenQASM, Q#, Braket, and more), and can be easily adjusted to other, more proprietary formats. The final circuits can then be executed on any quantum backend—hardware or simulator—by changing the backend name in the execution file.

The Classiq platform is fully integrated with IBM Quantum, Amazon AWS, Microsoft Azure, and other backend providers.

The Classiq analyzer tool analyzes and visualizes the quantum circuits at a functional level, providing additional design insights and allowing the loop to close in an automated design process.

## Predefined Models and Libraries¶

The Classiq platform natively includes several predefined models and libraries that can be modified and expanded to meet your specific needs:

- Quantum arithmetic model: You define complex arithmetic operations and synthesize gate-level circuits that apply these operations. The results are complex oracles, such as the Grover search framework uses.
- Combinatorial optimization model: You model custom combinatorial optimization problems (e.g., Max Vertex Cover or Max Independent Set) into gate-level circuits, while also significantly reducing the search space.
- Function library: Includes useful predefined functions, allowing flexible state preparation, controlling entanglement (Schmidt rank width) generation, and more.
- User-defined libraries: You define additional models and functions, describing quantum circuits that fit your individual, real-world use cases. You implement the provided interfaces, thus realizing an open-closed programming model.

## Application Suites¶

The Classiq platform provides full suites of models for common quantum applications. The suites provide massive flexibility and opportunity for fine-tuning. Concrete circuits generated from the models cover a broad range of the known application area:

- The finance application suite incorporates many financial use cases (option pricing, risk analysis, and more) based on the amplitude estimation framework. The underlying high-level model allows significant flexibility in describing the financial model and obtaining financial data.
- The chemistry application suite provides a framework for generating molecular Hamiltonians for any molecule, and solving the corresponding ground-state problem using quantum variational algorithms.

## Organization of This Guide¶

These are the tabs at the top of the screen:

- Getting Started provides installation instructions.
- The User Guide contains the theory, usage instructions, and practical hands-on examples of the platform functions.
- Sample Programs consolidates a large collection of examples found in the User Guide.
- The Reference Manual covers the complete syntax of all user-controlled functionalities.
- The Release Notes summarize the changes from version to version.