The chapter by David P. DiVincenzo discusses the physical implementation of quantum computation, focusing on the five key requirements for achieving scalable quantum computing and two additional requirements for quantum communication. These requirements are essential for creating a practical quantum computer and include: 1. **A scalable physical system with well-characterized qubits**: The system must contain qubits that can be accurately controlled and manipulated. 2. **The ability to initialize qubits to a simple fiducial state**: Qubits must be initialized to a known state before computation begins. 3. **Long relevant decoherence times**: Decoherence times must be significantly longer than the gate operation time to allow for quantum error correction. 4. **A "universal" set of quantum gates**: The system must support a set of quantum gates that can perform all necessary computational tasks. 5. **A qubit-specific measurement capability**: The system must be able to measure qubits without disturbing their state. Additionally, for quantum communication, the following requirements are essential: 6. **The ability to interconvert stationary and flying qubits**: The system must be able to convert qubits between a stationary state and a flying state. 7. **The ability to faithfully transmit flying qubits between specified locations**: The system must be able to transmit qubits over long distances without loss of information. DiVincenzo highlights the interdisciplinary nature of the field, involving atomic physics, quantum optics, nuclear and electron magnetic resonance spectroscopy, superconducting electronics, and quantum-dot physics. He also discusses the potential of various physical systems, such as ion traps, neutral atoms, solid-state devices, and superconducting devices, each with its own advantages and challenges. The chapter concludes by emphasizing the ongoing research and the potential for future advancements in quantum computing and communication.The chapter by David P. DiVincenzo discusses the physical implementation of quantum computation, focusing on the five key requirements for achieving scalable quantum computing and two additional requirements for quantum communication. These requirements are essential for creating a practical quantum computer and include: 1. **A scalable physical system with well-characterized qubits**: The system must contain qubits that can be accurately controlled and manipulated. 2. **The ability to initialize qubits to a simple fiducial state**: Qubits must be initialized to a known state before computation begins. 3. **Long relevant decoherence times**: Decoherence times must be significantly longer than the gate operation time to allow for quantum error correction. 4. **A "universal" set of quantum gates**: The system must support a set of quantum gates that can perform all necessary computational tasks. 5. **A qubit-specific measurement capability**: The system must be able to measure qubits without disturbing their state. Additionally, for quantum communication, the following requirements are essential: 6. **The ability to interconvert stationary and flying qubits**: The system must be able to convert qubits between a stationary state and a flying state. 7. **The ability to faithfully transmit flying qubits between specified locations**: The system must be able to transmit qubits over long distances without loss of information. DiVincenzo highlights the interdisciplinary nature of the field, involving atomic physics, quantum optics, nuclear and electron magnetic resonance spectroscopy, superconducting electronics, and quantum-dot physics. He also discusses the potential of various physical systems, such as ion traps, neutral atoms, solid-state devices, and superconducting devices, each with its own advantages and challenges. The chapter concludes by emphasizing the ongoing research and the potential for future advancements in quantum computing and communication.