The ability of a quantum system such as a qubit to be in a state formed by adding several states, such as |0⟩ and |1⟩, with complex amplitudes. A measurement gives one of the outcomes at random, and differences in the phases of the amplitudes affect the results through interference.
Japanese name: 量子重ね合わせ
Quantum superposition appears in 10 practice questions across 1 topic, including Quantum Computing Hardware.
Field: Quantum Computing Hardware
Answer: A. 25 ns
Under continuous microwave driving, the probability of being in |1⟩ oscillates as sin²(Ωt/2) with Ω = 2π × 10 MHz, and the period of one round trip is 1 ÷ 10 MHz = 100 ns. The rotation angle Ωt reaches π/2 at t = 25 ns, when the probability of being in |1⟩ is 50%. A rotation angle of π (50 ns) is an X gate (π pulse) that swaps |0⟩ and |1⟩, and 2π (100 ns) returns the qubit to |0⟩. The rotation angle is set by the pulse amplitude and length, so errors in the microwave amplitude or timing translate directly into gate errors.
A superposition is not a value halfway between 0 and 1: a measurement always gives either 0 or 1.
Which statement about a qubit is correct?The state of n qubits is a superposition of the 2ⁿ basis states from |00…0⟩ to |11…1⟩, each with its own probability amplitude.
How many probability amplitudes (complex numbers) are neede…This state is a superposition of |00⟩ and |11⟩ with no |01⟩ or |10⟩ component, so the two measurement results always agree.
Two qubits are in the entangled state (|00⟩ + |11⟩)/√2. Whi…Applied to a superposition α|0⟩ + β|1⟩, it swaps the amplitudes to give β|0⟩ + α|1⟩.
Which correctly describes what a single-qubit X gate does?The H gate is often used at the start of quantum algorithms to create an equal superposition of all basis states.
A qubit in the state |0⟩ has a Hadamard (H) gate applied on…As an Amazon Associate I earn from qualifying purchases.
Qubit Quantum entanglement Quantum error correction Time constant Decoherence Dilution refrigerator Ion trap Josephson junction NISQ Post-quantum cryptography