1. What does decoherence describe?Degradation of quantum coherence through interaction with the surroundingsAn intended state change caused by an ideal gateOnly the complete physical disappearance of a photonOnly a mistaken classical label in a stored measurement record

2. Which example most directly illustrates photon loss?A local gate rotates a stored qubit by the wrong angleA detector reports 1 when the stored qubit was prepared as 0A photon expected at a detector fails to arriveUncontrolled phase changes alter a stored qubit's interference

3. What does a herald tell a controller?The output state has been proved perfectly noiselessA specified success condition has been signalledAll future gates will return correct resultsThe input's complete unknown quantum state has been read

4. Why is heralding different from fidelity?They are two names for the number of pairs produced per secondA herald gives an exact numerical fidelity for each individual stateA high target-state fidelity determines how many generation attempts failHeralding signals an event; fidelity compares quality with a target

5. What is a physical qubit?An automatically protected collection of perfect backupsA hardware carrier of quantum informationA classical correction message containing two bitsThe complete output of every run of an algorithm

6. What is a logical qubit in an error-correcting scheme?Quantum information represented within an encodingAny one bare qubit renamed after a successful gateA physical carrier used only for network communicationA qubit identified solely by having a high single-gate fidelity

7. Why does quantum error correction not violate no-cloning?It suspends quantum mechanics during an error checkIt first measures and learns every unknown amplitude exactlyIt produces copies only when a classical network is availableIt encodes information in a joint state instead of producing independent copies

8. What is an error syndrome used for?Reading the entire encoded unknown state directlyGiving the total number of physical qubits in a moduleInferring error information and selecting an appropriate responseReporting only whether a communication photon arrived

9. Why can stored data degrade while waiting for entanglement?Qubits have no physical state during a waitWaiting always creates an extra copyNoise can act even when no intended gate is runningEvery storage interval necessarily measures the data in the computational basis

10. A hypothetical link makes 100 attempts per second with 10% success per attempt. Ignoring overhead, what is its expected heralded rate?1 pair per second90 pairs per second1000 pairs per second10 pairs per second

11. With independent attempts and fixed success probability 0.10, what is the expected number of attempts until success?100.105100

12. The hypothetical heralded states have fidelity 0.95 to a target Bell state. Which conclusion is justified?Exactly 95% of all generation attempts succeededTheir quality was compared with that target under the stated fidelity definitionEvery algorithm using them succeeds with probability 0.95The link produces exactly 95 pairs per second

13. What type of hardware did Main and colleagues connect in the cited 2025 experiment?Two unconnected classical laptop processorsA worldwide network of fault-tolerant superconducting processorsTwo purely simulated nodes with no laboratory hardwareTwo trapped-ion modules linked optically

14. How should the reported 86% and 71% figures in that experiment be read?86% Grover-search success and 71% remote-CZ gate fidelityApproximately 86% remote-CZ gate fidelity and 71% Grover-search success86% Bell-pair generation success and 71% photon transmission86% single-qubit readout fidelity and 71% entangled-state fidelity

15. What does the 2025 two-module demonstration establish on its own?That distributed computers beat classical computers on every taskThat worldwide fault-tolerant computing is already solvedAn experimental implementation of distributed operations under its reported conditionsThat adding modules never adds noise

16. What should be checked when a vendor announces a large qubit count?Whether the count refers to physical carriers, logical information or access to separate machinesOnly whether the raw count exceeds another device's countOnly the best local gate fidelity, regardless of encoding and linksOnly how many shots were used in a benchmark circuit

17. Why ask whether unsuccessful runs were discarded from a reported result?Filtering changes which runs contribute and can affect the practical cost of accepted resultsDiscarding any run proves that all remaining runs are perfectThe number of accepted runs always equals the number attemptedA paper cannot report a valid conditional result

18. Which statement about error mitigation is safest?It always creates a protected logical qubitIt removes every physical noise source permanentlyIt should not automatically be equated with fully error-corrected computationIt makes classical communication unnecessary

19. What makes a performance comparison meaningful?Comparing different tasks only by processor countComparing gate times while excluding entanglement preparationComparing one device's state fidelity with another's application success rateThe same task and success criterion, with total resources and uncertainty described

20. What is a responsible next step after completing this introductory course?Treat every roadmap target as a completed experimentRead a primary paper's methods and connect each metric to the capability it actually testsAssume every networked machine is fault tolerantUse module count alone to predict all application speedups

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