A quantum computer is

A quantum computer is

• A. A computer that uses transistors to process data
• B. A computer that uses photons to compute
• C. A device to store classical memory
• D. A computer that uses qubits to process many states at once using quantum mechanics

Answer: (D)

The main idea is that quantum computing uses qubits that can be in superpositions of 0 and 1, which lets the machine explore many possible states in parallel and use interference to amplify correct results. This combination—qubits plus the rules of quantum mechanics—gives a form of processing that goes beyond classical bit-by-bit computation. Choosing the description that mentions qubits and processing many states at once captures this core capability: qubits are the essential resource, and their ability to hold multiple states simultaneously is what enables quantum parallelism. The other statements describe classical ideas—transistors and binary bits for ordinary computers, or memory storage only—and, while there are physical realizations using photons or other approaches, they don’t define what a quantum computer is.

The main idea is that quantum computing uses qubits that can be in superpositions of 0 and 1, which lets the machine explore many possible states in parallel and use interference to amplify correct results. This combination—qubits plus the rules of quantum mechanics—gives a form of processing that goes beyond classical bit-by-bit computation.

Choosing the description that mentions qubits and processing many states at once captures this core capability: qubits are the essential resource, and their ability to hold multiple states simultaneously is what enables quantum parallelism. The other statements describe classical ideas—transistors and binary bits for ordinary computers, or memory storage only—and, while there are physical realizations using photons or other approaches, they don’t define what a quantum computer is.