50 IBM A1000-112: Assessment: Fundamentals of Quantum Computation Using Qiskit v0.2x Developer Practice Questions: Question Bank 2025

You initialize a single qubit in the state |0⟩ and apply an H gate, then measure in the computational (Z) basis. What outcome distribution should you expect (ideal, noiseless)?

In Qiskit, you build a circuit with quantum operations but do not add any measurements. After executing it on a backend, you call result.get_counts(circuit). What is the most likely outcome?

You want to create a Bell state in a 2-qubit circuit. Which sequence is correct (starting from |00⟩)?

You are choosing between running a circuit on a statevector simulator versus a real quantum device. Which statement best describes a key practical difference?

A team needs to run the same parameterized circuit for many different parameter values efficiently. Which approach is recommended in Qiskit?

You run Grover's algorithm on a small search space. After the Grover iterations, which measurement outcome is expected to have the highest probability (ideal conditions)?

A circuit runs successfully on a simulator but fails on a real backend with an error related to unsupported instructions or basis gates. What is the most appropriate fix?

You need to compare results from two circuit variants fairly on a noisy backend. Which practice best reduces run-to-run variability when collecting counts?

You prepare a Bell state and then measure both qubits in the Z basis. On ideal hardware, which result best indicates entanglement rather than independent randomness?

A developer uses an Aer qasm simulator with a device-derived noise model to estimate performance. Their results differ significantly from running on the actual device, even with the same circuit and shot count. Which factor is the most plausible reason?

A learner measures a single qubit that was prepared in the state |1⟩. Which measurement result distribution is expected in the computational (Z) basis?

In Qiskit, a developer wants to sample results from a quantum circuit and view counts of bitstrings. Which is the most appropriate approach?

A team member says, "If a two-qubit state is entangled, it can be written as a tensor product of two single-qubit states." What is the correct response?

A developer runs a circuit on a simulator and obtains a statevector. They then add measurements to the circuit and run again, but the statevector output is no longer available. What is the best explanation?

A circuit is intended to create the Bell state (|00⟩+|11⟩)/√2. The developer applies H on qubit 0 and then CX with control=0 and target=1, followed by measurement. Which result is most likely when running many shots on an ideal simulator?

A developer is troubleshooting why a circuit fails on a given hardware backend due to unsupported operations. Which workflow is recommended to make the circuit compatible with the backend?

A developer wants to compare two candidate circuits for the same task and chooses the one with fewer two-qubit gates when targeting a NISQ device. Why is this generally a good strategy?

In Grover’s search, a developer uses a single Grover iteration on a 2-qubit search space (N=4) with one marked item. What is the key effect of the Grover iteration?

A developer implements a Bernstein–Vazirani circuit but observes uniformly random outputs instead of a fixed hidden bitstring. Which issue is the most likely cause?

A developer wants to run circuits on hardware but also needs to mitigate readout errors using calibration data. Which approach best matches this requirement at a high level?

A developer prepares a single qubit in the state |+> and measures it in the computational (Z) basis. Which outcome distribution is expected over many shots?

In Qiskit, a user runs a circuit and receives a counts dictionary like {'0': 521, '1': 503}. What does this dictionary represent?

A team wants to demonstrate quantum entanglement using a minimal 2-qubit circuit and measurements in the Z basis. Which circuit is the standard approach to create a Bell state (|00> + |11>)/sqrt(2) before measurement?

A developer uses a 2-qubit circuit but only creates a ClassicalRegister of size 1 and then tries to measure both qubits into it. The code errors at circuit construction time. What is the most likely fix?

A user needs to execute the same parameterized circuit for many different angle values efficiently. Which approach best reduces recompilation overhead?

A circuit includes a mid-circuit measurement followed by a classically conditioned X gate (apply X only if the measured bit is 1). The circuit behaves correctly on a simulator but fails on a chosen hardware backend. What is the most likely reason?

A developer is comparing two transpiled versions of the same circuit for hardware execution. One has lower depth but more two-qubit gates; the other has higher depth but fewer two-qubit gates. Which choice is generally the better best practice for noisy hardware, assuming all else is equal?

A researcher simulates a circuit with noise to better match hardware results, and wants to include readout (measurement) error. Which approach is most appropriate in Qiskit simulations?

A team is implementing Grover’s algorithm for a small search space. After applying the oracle and the diffusion operator once, they observe that the marked state probability increases. Conceptually, what does the diffusion operator do?

A developer needs to run a circuit on a device with limited qubit connectivity. The circuit has CNOTs between many non-adjacent logical qubits. After transpilation, the output has many SWAP gates and the results degrade. Which design-time action most directly reduces SWAP insertion?

A learner prepares a single qubit in the state |+⟩ and measures it in the computational (Z) basis. What measurement outcome distribution should they expect over many shots (ignoring noise)?

You build a circuit with 2 qubits and 2 classical bits, then call measure_all(). You expect two classical bits in the output string. Instead, you see more classical bits than expected. What is the most likely cause?

In a variational algorithm (e.g., VQE), which component is typically responsible for proposing new parameter values from one iteration to the next?

A team wants to compare two circuits fairly by reducing statistical fluctuations in their measurement results. Which approach is most appropriate?

You want to execute the same parameterized circuit for many different parameter values efficiently (e.g., a sweep for calibration). What is a best practice in Qiskit?

A circuit is intended to create a Bell state and then measure both qubits. The developer runs on a qasm-style simulator and gets no measurement counts (an empty result or a KeyError when accessing counts). Which is the most likely issue?

In Grover's algorithm, what is the primary purpose of the diffusion (inversion-about-the-mean) operator?

A developer transpires a circuit for a specific device and receives an error indicating that a two-qubit gate is not supported on the chosen qubit pair. What is the best next step to make the circuit executable?

A researcher wants the expectation value of an observable (e.g., a Hamiltonian term) from a circuit run on a shot-based backend. Which approach is correct?

A team is building a repeatable benchmark suite. They need results that are deterministic given the same code and environment when using a simulator (for regression testing). Which is the most appropriate practice?

You want to measure a 2-qubit circuit and store each qubit’s result in a separate classical bit (c0 for q0, c1 for q1). Which Qiskit statement correctly performs this mapping?

In the Bloch sphere representation, which gate maps |0⟩ to |1⟩ (ignoring global phase)?

You are reviewing results from a simulator with measurement shots. The counts dictionary sums to the number of shots. What does an individual key like '01' represent?

A developer creates a Bell state and measures both qubits. They expect only '00' and '11' outcomes, but also see '01' and '10' with small frequencies on a real device. What is the most likely explanation?

You need to conditionally apply an X gate to qubit q0 only when a previous measurement stored in classical bit c0 equals 1. Which approach is recommended in Qiskit circuit construction?

A team wants to compare an ideal, noise-free distribution to a more realistic noisy result for the same circuit. Which pairing best matches this goal?

In Grover’s algorithm, why does the diffusion operator (inversion about the mean) increase the probability of measuring the marked state after an oracle call?

You transpile a circuit for a specific backend and observe that additional SWAP gates were inserted. What is the most common reason for this during compilation?

You are implementing phase estimation and need to apply controlled-U^(2^k) operations for multiple k values. Which strategy typically reduces circuit depth compared to repeating U many times?

A circuit uses a mid-circuit measurement and then conditionally applies gates based on that result. When targeting a real backend, the job fails or produces unexpected behavior. What is the best troubleshooting step to take first?