Quantum Computing

1. Basics of Quantum Computing

• Quantum Bit (Qubit): Unit of quantum information. Can be 0, 1, or a superposition of both.
• Superposition: Qubit exists in multiple states simultaneously until measured.
• Entanglement: Strong correlation between qubits; measuring one affects the other.
• Quantum Interference: Probability amplitudes can add or cancel, crucial for quantum algorithms.

---

2. Quantum Gates

• Act like logic gates for qubits; manipulate qubit states.
• Hadamard (H): Creates superposition.
• Pauli-X (NOT): Flips qubit state.
• CNOT (Controlled NOT): Entangles two qubits.
• Phase Gates (Z, S, T): Change the phase of a qubit.

---

3. Quantum Algorithms

• Shor’s Algorithm: Efficiently factors large numbers (used for breaking RSA encryption).
• Grover’s Algorithm: Speeds up unstructured database searches (√N time).
• Deutsch-Jozsa Algorithm: Solves problems faster than classical algorithms.

---

4. Quantum Circuits

• Input Qubits: Initialized to a specific state.
• Quantum Gates: Applied in sequence to perform operations.
• Measurement: Collapse qubits to classical bits (0 or 1).

---

5. Key Concepts

• Quantum Speedup: Achieved for certain problems (e.g., factoring, search).
• Quantum Decoherence: Loss of quantum information due to the environment.
• No-Cloning Theorem: Qubits cannot be copied exactly.

---

6. Quantum Computing Models

• Gate Model: Uses quantum gates to process information (e.g., IBM Q).
• Adiabatic Quantum Computing: Slowly evolves the system to find the ground state.
• Quantum Annealing: Solves optimization problems (e.g., D-Wave systems).

---

7. Quantum Hardware

• Superconducting Qubits: Use Josephson junctions (e.g., IBM, Google).
• Trapped Ions: Use ions trapped by electromagnetic fields.
• Photonic Qubits: Use photons for computation.
• Topological Qubits: Based on braiding quasiparticles (future tech).

---

8. Applications

• Cryptography: Breaking RSA, quantum key distribution (QKD).
• Machine Learning: Speed up training and data analysis.
• Optimization: Logistics, finance, and AI applications.
• Chemistry/Physics: Simulating molecules and quantum systems.

---

9. Challenges

• Scalability: Building large-scale quantum computers.
• Error Correction: Overcoming quantum noise.
• Physical Limitations: Maintaining qubits at near-absolute-zero temperatures.

---

10. Quantum Computing Companies

• IBM Quantum: Offers cloud-accessible quantum computers.
• Google Quantum AI: Achieved quantum supremacy with Sycamore.
• Rigetti, D-Wave, Honeywell, IonQ: Leading companies in quantum research.

---

11. Important Terms

• Quantum Supremacy: Demonstrating a quantum task no classical computer can perform in reasonable time.
• Quantum Volume: Measures computational power of a quantum computer.
• Bra-ket Notation: Used to represent quantum states.

---

Quick Acronyms

• QEC: Quantum Error Correction.
• QKD: Quantum Key Distribution.
• CNOT: Controlled NOT Gate.

---

• X
• Instagram
• WhatsApp