Quantum Circuit Simulator

This project is a simplified Quantum Circuit Simulator written in C. The simulator supports arbitrary quantum gates represented as matrices of complex numbers, and applies them to an initial state provided as input.

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🧠 Project Structure

The project is organized into the following files:

• main.c – Main function: handles parsing, execution, and output of the circuit.
• parser.c/.h – Parser for input files containing initial state and circuit definitions.
• circuit.c/.h – Data structures and functions to build and execute the quantum circuit.
• complex.c/.h – Definition of the complex type and operations on complex numbers.
• Makefile – Build automation.

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⚙️ Building

To compile the project, simply run:

make

This will compile all .c files and produce the executable qsim.

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▶️ Execution

With custom files

Run the simulator specifying the two input files:

./qsim [init_file] [circuit_file]

Example:

./qsim init-ex.txt circ-ex.txt

Without arguments

If no arguments are provided, the program uses the default files in the current directory:

• init-ex.txt
• circ-ex.txt

./qsim

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🗂️ Input File Format

init-ex.txt – Initial State

#qubits 1

#init [0.5+i0.5, 0.5-i0.5]

• #qubits: number of qubits (integer ≥ 1).

• #init: vector of complex numbers in square brackets, separated by commas.

  • Supported formats: a+ib.
  • a and b are any real number in the form of int_part.decimal_part e.g. -3.91

circ-ex.txt – Circuit Definition

#define X [(0, 1) (1, 0)]

#define I [(1, 0) (0, 1)]

#define Y [(0, -i) (i, 0)]

#circ Y X I

• #define <letter>: defines a square matrix of size 2^n x 2^n (quantum gate). <letter> must be a single ASCII character.
• #circ: sequence of letters representing the gates to apply to the initial state in order.

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🖨️ Output

The simulator prints to stdout:

Final State: complex vector resulting from sequentially applying the gates to the initial state.

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❗ Notes

• Gate matrices must be square and compatible with the specified number of qubits.
• Complex numbers are printed in the form a+ib.

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👨‍💻 Author

Vincenzo Computer Science Student – Sapienza University of Rome