quaco.js/src/Algorithms/DeutschJozsa.js

A lightweight modular Quantum Computing Simulator in JavaScript. Supports qubits, quantum gates, entanglement, circuits, algorithms, and visualization.

// src/Algorithms/DeutschJozsa.js

import { Simulator } from '../Simulator.js';
import { QuantumGate } from '../QuantumGate.js';

/**
 * Deutsch-Jozsa Algorithm Simulator
 */
export class DeutschJozsa {
    /**
     * Runs the Deutsch-Jozsa algorithm.
     * @param {number} numInputQubits - number of input qubits
     * @param {'constant'|'balanced'} oracleType - type of oracle function
     * @returns {string} 'constant' or 'balanced' prediction
     */
    static run(numInputQubits, oracleType = 'balanced') {
        const sim = new Simulator(numInputQubits + 1);

        // Step 1: Prepare input qubits |0...0⟩ and output qubit |1⟩
        sim.addGate(QuantumGate.x(), numInputQubits); // Flip last qubit to |1⟩

        // Step 2: Hadamard on all qubits
        for (let i = 0; i <= numInputQubits; i++) {
            sim.addGate(QuantumGate.hadamard(), i);
        }

        // Step 3: Apply oracle
        if (oracleType === 'constant') {
            // Do nothing for constant 0
            // (or flip all for constant 1)
        } else if (oracleType === 'balanced') {
            // For simulation, apply CNOT from each input qubit to output
            for (let i = 0; i < numInputQubits; i++) {
                sim.addCNOT(i, numInputQubits);
            }
        } else {
            throw new Error('Unsupported oracle type');
        }

        // Step 4: Hadamard again on input qubits (not output)
        for (let i = 0; i < numInputQubits; i++) {
            sim.addGate(QuantumGate.hadamard(), i);
        }

        // Step 5: Measurement
        const results = sim.run(1); // Single shot is enough
        const measuredInput = results.slice(0, numInputQubits); // Ignore last qubit

        // Step 6: Analyze
        if (measuredInput === '0'.repeat(numInputQubits)) {
            return 'constant';
        } else {
            return 'balanced';
        }
    }
}