50 IBM A1000-128 Practice Questions: Question Bank 2025

A learner is new to quantum computing and asks why measuring a qubit changes what you can know about its state. Which statement best explains measurement in quantum computing?

A developer wants to create a Bell pair to demonstrate entanglement on a simulator. Which circuit sequence is correct starting from |00>?

A user runs a circuit on real hardware and observes results different from the ideal simulator. Which factor is the most common cause of the discrepancy?

A team wants to reduce the impact of readout (measurement) errors when running circuits on IBM Quantum hardware. Which approach is a common mitigation technique?

A circuit applies an X gate to a qubit initially in |0> and then measures it in the computational basis. What outcome is expected in an ideal execution?

A developer writes a parameterized circuit and wants to run it for many different parameter values efficiently on IBM Quantum services. Which method is generally recommended?

A circuit produces 3-bit measurement strings. After 2000 shots, the counts are roughly half '000' and half '111', with very few other bitstrings. What is the most likely explanation?

A scientist needs to choose between an ideal statevector simulator and a noisy simulator when prototyping a circuit intended for hardware. What is the best practice to increase confidence that results will translate to hardware behavior?

A team is designing a variational algorithm (e.g., VQE/QAOA) to run on near-term hardware. Which design choice most directly helps reduce error from decoherence while preserving expressivity?

A logistics company is evaluating quantum approaches for optimization problems (e.g., routing). They want a near-term method that can run on noisy devices and can incorporate problem constraints. Which option best fits this need?

A new team member says a qubit is just a classical bit that is sometimes 0 and sometimes 1. Which statement best corrects this misunderstanding?

You run a circuit on real hardware and notice results differ from the ideal simulator, especially for deeper circuits. Which is the most likely cause?

In Qiskit, you want to read out all measured qubits as a histogram of bitstrings. Which object most directly represents the measurement outcomes from an execution?

A researcher prepares a Bell pair and measures both qubits in the Z basis. They expect correlated results. Which circuit is the standard way to create the |Φ+⟩ state from |00⟩?

You transpile a circuit for a specific IBM Quantum backend and see additional SWAP operations inserted. What is the most common reason this happens?

A team wants to estimate the expected value of an observable (e.g., ⟨Z⟩) from measurement results. Which approach is most appropriate?

A developer uses a local simulator to validate logic and then wants to run the same circuit on an IBM Quantum device. Which best practice helps ensure the circuit is compatible with the target device?

A logistics company is exploring quantum computing for route optimization. They are evaluating whether quantum is appropriate now. Which statement is the most accurate at a foundational level?

You need to measure an observable that is not diagonal in the computational (Z) basis, such as X on a qubit. What should you do before measurement to obtain X-basis statistics using standard Z-basis measurement hardware?

A user runs the same circuit multiple times on hardware and sees the most frequent bitstring change between runs, even with the same number of shots. They suspect the circuit is wrong, but it matches the simulator. Which is the best explanation and action at a foundational level?

A team is new to quantum computing and asks what makes a qubit fundamentally different from a classical bit. Which statement is most accurate?

A developer wants to produce a uniform random bit in an IBM Quantum circuit. Which approach is most appropriate?

An engineer is comparing classical simulation with running a circuit on real quantum hardware. Which statement best describes a practical difference they should expect?

A researcher needs to prepare the Bell state (|00> + |11>)/sqrt(2) starting from |00>. Which gate sequence is correct?

A developer runs a circuit with 1000 shots and expects probabilities near 50/50 for two outcomes, but sees 530 vs 470 counts. They suspect something is wrong. What is the best explanation?

A circuit works in a simulator but performs poorly on hardware. The circuit has many two-qubit gates and a long depth. Which action is most likely to improve hardware results while keeping the algorithm intent?

A team is evaluating whether a near-term quantum approach is suitable for exploring low-energy configurations of a small molecule. Which use case best aligns with near-term quantum capabilities?

A user expects two qubits to be entangled after running a circuit, but the measurement results show no correlation. Which issue most directly explains the absence of entanglement?

A developer notices that in a transpiled circuit for hardware, additional SWAP operations appear and the circuit depth increases significantly. What is the most likely reason?

A product team proposes using Grover’s algorithm to speed up searching an unsorted database of size N on near-term hardware. Which statement best reflects the realistic expectation?

A learner says, "Measuring one qubit in an entangled pair instantly sends a signal to the other qubit." Which correction best matches quantum fundamentals?

You run a circuit that should create a Bell state: apply H on qubit 0, then CX with control 0 target 1, then measure both. In the results, you see nearly uniform counts across 00, 01, 10, 11. Which is the most likely cause?

A team wants to reduce the impact of noise when estimating an expectation value from repeated circuit executions on real hardware. Which technique is most directly aimed at correcting readout (measurement) errors?

Which statement best describes what a qubit’s measurement does in the computational basis?

A developer is building a circuit that must run on a specific IBM Quantum device with limited qubit connectivity. What is the recommended approach to ensure the circuit respects the device’s coupling map?

A scientist wants to use a quantum computer to estimate the ground-state energy of a small molecule as a proof of concept. Which approach is most commonly associated with near-term (NISQ) hardware for this task?

A team uses a parameterized circuit to approximate a target state, but optimization frequently gets stuck with near-zero gradients for many parameters. Which phenomenon best explains this behavior in variational algorithms?

A circuit produces correct results on an ideal simulator but performs poorly on real hardware. The team suspects the circuit is too deep and sensitive to noise. Which change is the best first step to improve success probability while preserving the algorithm’s intent?

A workflow needs to run the same circuit many times with different parameter values (e.g., for a variational algorithm). Which design choice is most appropriate for efficient execution on quantum hardware services?

You want to estimate an observable’s expectation value for a quantum state prepared by a circuit, but the observable is a sum of Pauli terms (a Hamiltonian). On real hardware, what is the standard method to obtain the expectation value?

A learner is asked to describe what a measurement does in a quantum circuit. Which statement is MOST accurate?

A developer wants to create a Bell state using the fewest standard gates. Which circuit is the correct minimal approach starting from |00>?

A team is deciding how to validate a quantum circuit before running it on real hardware. What is the recommended first step to reduce wasted device time?

A circuit produces the correct results on a simulator but different results on real hardware, even with many shots. Which factor is the MOST likely cause?

A developer writes a circuit that uses a 3-qubit Toffoli (CCX) gate, but the target backend does not natively support CCX. What should the developer expect the tooling to do when preparing the circuit for that backend?

A user runs a circuit and observes that the bitstring results appear to have qubit order reversed from what they expected. Which action is the BEST way to confirm and resolve the mapping confusion?

A financial services team wants an early-stage quantum approach to explore portfolio optimization under constraints, understanding that near-term devices are limited. Which use case is MOST aligned with foundational quantum application patterns?

A researcher implements a variational circuit (e.g., for VQE) and notices the optimizer stops improving early. Which change is MOST likely to help in a practical, noise-aware workflow?

A team submits a circuit to a backend and receives an error indicating that the circuit cannot be mapped to the device connectivity with the current settings. What is the MOST appropriate resolution?

A developer prepares an entangled two-qubit state and then applies a Z gate to only one qubit before measuring in the computational basis. The measured probabilities remain unchanged compared to not applying Z. What is the BEST explanation?