Classical gates and quantum gates are fundamentally different in their operation and underlying principles, which is why classical gates cannot be directly used in quantum computing. Here are some key reasons for this:
Superposition: One of the fundamental principles of quantum computing is the ability of quantum bits, or qubits, to exist in superposition states. Superposition allows qubits to represent multiple states simultaneously, whereas classical bits can only be in one state (0 or 1) at a time. Quantum gates are designed to manipulate and take advantage of the properties of qubits in superposition, enabling complex computations.
Entanglement: Quantum entanglement is another distinct feature of quantum computing. Entanglement allows qubits to become correlated in such a way that the state of one qubit is dependent on the state of another, regardless of the physical distance between them. Classical gates do not have an equivalent concept of entanglement, which is crucial for various quantum algorithms and protocols.
No-Cloning Theorem: In quantum mechanics, there is a fundamental principle known as the no-cloning theorem. It states that it is impossible to create an exact copy of an arbitrary unknown quantum state. This contrasts with classical bits, which can be easily duplicated. The no-cloning theorem has profound implications for information processing in quantum systems and restricts the operations that can be performed on qubits.
Measurement: Quantum computing involves the measurement of qubits to extract useful information. However, quantum measurements are probabilistic in nature and introduce randomness into the system. Classical gates, on the other hand, rely on deterministic measurements, where the output is precisely determined by the input. The probabilistic nature of quantum measurements is a crucial aspect of quantum algorithms and sets them apart from classical computation.
Given these fundamental differences, dedicated quantum gates are designed to exploit the unique properties of qubits, allowing for quantum information processing and computation. These gates operate on superposition, entanglement, and probabilistic measurements, which are essential elements in quantum algorithms and protocols.