50 IBM A1000-099: Assessment: Foundations of Quantum Computing Practice Questions: Question Bank 2025

A developer explains qubits to a non-technical stakeholder. Which statement best captures why a qubit differs from a classical bit?

You run a circuit multiple times on a quantum backend and observe a distribution of bitstrings rather than a single deterministic result. What is the primary reason?

A student applies a Hadamard (H) gate to a qubit initialized in |0⟩. What is the expected measurement probability in the computational basis?

A team wants a quick way to validate a small quantum circuit’s expected output distribution without worrying about device noise. Which approach is most appropriate?

In a circuit with two qubits, you want to create entanglement starting from |00⟩. Which gate sequence is the standard minimal approach?

A circuit produces the correct results on an ideal simulator but gives noticeably different results on real hardware. Which explanation is most likely?

A user writes a circuit with a mid-circuit measurement and then applies a gate conditioned on that measurement result. What capability is required to express this behavior?

A data scientist is evaluating whether a problem is a good candidate for near-term (NISQ) quantum approaches. Which task is most aligned with commonly explored NISQ applications?

A circuit aims to demonstrate phase kickback by applying a controlled-U operation where U adds a phase of -1 to |1⟩ (i.e., U = Z). The control qubit is prepared in |+⟩ and the target in an eigenstate of Z. Which outcome best describes what happens to the control after the controlled-Z interaction when the target is |1⟩?

A developer wants to run a circuit on IBM quantum hardware but finds that their two-qubit gates are being rewritten into a different set of operations and the qubit indices are reassigned. What is the most accurate reason for this transformation?

A researcher measures a single qubit and obtains |1⟩ 25% of the time over many shots. Assuming an ideal projective measurement in the computational basis, what is the most likely state (up to a global phase)?

In IBM Quantum circuit diagrams, what is the effect of placing an X gate on a qubit initialized to |0⟩?

A user runs the same circuit multiple times on a real IBM Quantum device and observes slightly different outcome distributions across jobs. Which factor most directly explains this behavior?

You need to create the Bell state (|00⟩ + |11⟩)/√2 from |00⟩. Which gate sequence accomplishes this on two qubits q0 and q1?

A circuit uses a CZ gate, but the target backend natively supports CX. Which statement best describes what the transpiler will typically do?

A team wants to compare an ideal (noise-free) result with a noisy hardware-like result for the same circuit before using real quantum time. Which approach best fits IBM Quantum best practices?

In Grover's search on N items with one marked solution, what is the primary role of the diffusion (inversion-about-the-mean) operator?

You run a 2-qubit circuit with 1024 shots and see results reported as counts like {'00': 510, '11': 514}. Which interpretation is correct?

A circuit prepares (|0⟩ + |1⟩)/√2 on q0 and (|0⟩ - |1⟩)/√2 on q1, then applies a CX with q0 as control and q1 as target. What is the resulting two-qubit state?

You must run a 6-qubit circuit on hardware, but transpilation introduces many extra two-qubit gates due to limited connectivity, harming fidelity. Which design choice most directly reduces this overhead?

A researcher measures the first qubit of a 2-qubit system and wants to predict what happens to the overall quantum state immediately after that measurement. Which statement best describes the effect of measuring one qubit in an entangled system?

In a circuit diagram, which gate is its own inverse (applying it twice returns the qubit to its original state) and also flips the computational basis states |0⟩ and |1⟩?

A student runs a circuit on a simulator and wants the full complex amplitudes of the statevector (not just measurement probabilities). Which approach is most appropriate on IBM quantum tooling?

A developer expects a 2-qubit Bell state, but the measurement results are ~50% "00" and ~50% "10" instead of "00" and "11". The circuit is: H on qubit 0, then CNOT with qubit 1 as control and qubit 0 as target. What is the most likely issue?

A team wants to compare results from hardware runs taken on different days. They suspect device drift and varying noise levels are affecting outcomes. What is a recommended best practice to improve comparability of runs on IBM Quantum hardware?

A proof-of-concept uses a variational algorithm where a classical optimizer updates circuit parameters based on measured expectation values. Which statement best characterizes why shots are needed in this workflow on real hardware?

A user submits a circuit to hardware and receives an error indicating the circuit uses an operation not supported by the backend's basis gates. What is the most appropriate way to resolve this?

A circuit needs a controlled-Z (CZ) gate, but the backend natively supports CNOT and single-qubit gates. Which decomposition is correct (up to global phase) using Hadamard gates on the target qubit?

A developer claims they can clone an unknown qubit state |ψ⟩ to create two identical copies using a quantum circuit, which would allow them to measure one copy and keep the other for later computation. Which principle explains why this is not generally possible?

A team wants to use Grover's algorithm to search an unstructured database of size N. They ask how the number of oracle calls scales compared to classical exhaustive search. Which answer is correct?

A student measures a single qubit prepared in the state |+> in the Z (computational) basis. What measurement outcome distribution should they expect?

Which statement best describes a key difference between a classical bit and a qubit?

In a quantum circuit, what is the primary effect of applying an X gate to a qubit?

A team is comparing running a circuit on an ideal simulator versus real IBM Quantum hardware. Which result is most expected when moving from simulator to hardware?

You prepare two qubits in the state |00>, apply an H gate to qubit 0, then apply a CNOT with qubit 0 as control and qubit 1 as target. What is the resulting state?

A researcher wants to estimate the expected value of an observable by sampling measurement outcomes many times. In IBM Quantum terminology, what does increasing the number of "shots" primarily do?

A circuit includes multiple gates that depend on the measurement outcome of a qubit earlier in the circuit (feed-forward). What is the recommended approach when this dynamic behavior is not supported on the selected backend?

A product team is evaluating whether Grover's algorithm is appropriate for a search problem. Which statement best reflects its expected advantage under ideal conditions?

A developer runs a circuit on hardware and notices outcomes that violate an expected symmetry, likely due to measurement (readout) bias between |0> and |1>. Which mitigation technique most directly targets this issue?

You need to run a 6-qubit circuit heavy in two-qubit gates on a device where not all qubits are directly connected. What is a common consequence of limited connectivity, and why does it matter?

A learner measures a single qubit prepared in the state |+>. What outcome distribution should they expect when measuring in the computational (Z) basis?

In IBM Quantum, what is the primary purpose of a transpiler when running a circuit on real hardware?

Which statement best describes a qubit in contrast to a classical bit?

A circuit applies an H gate followed immediately by another H gate on the same qubit, then measures in the Z basis. Assuming the qubit started in |0>, what is the expected measurement result (ignoring noise)?

A developer runs a circuit on a real IBM Quantum backend and sees results that differ from an ideal simulator. Which is the most likely primary reason?

A team needs to estimate the expectation value of an observable from a circuit execution. What IBM Quantum execution setting most directly controls the statistical sampling error of the measured estimate?

A circuit prepares the 2-qubit state by applying H on qubit 0 followed by CNOT with control qubit 0 and target qubit 1. What state is produced (up to a global phase)?

A product team is evaluating whether to use Grover's algorithm for search. For an unstructured search space of size N with one marked item, what is the expected query complexity scaling of Grover's algorithm compared to classical exhaustive search?

A 3-qubit circuit uses a two-qubit gate between qubits that are not directly connected on the target IBM Quantum device. What is the most likely consequence after transpilation?

A researcher tries to clone an unknown qubit state |ψ> to create two identical copies for later measurements. Which fundamental principle explains why no quantum circuit can perfectly accomplish this for all |ψ>?