Quiz: Why Quantum Computing?
This quiz checks the main ideas from Chapter 1.
Multiple choice questions
1. What is a classical bit?
A. A tiny battery
B. A value that is either 0 or 1
C. A quantum particle
D. A type of computer screen
2. What is a qubit?
A. A quantum version of a bit B. A computer virus C. A type of classical wire D. A number bigger than a byte
3. What can happen when we measure a qubit?
A. We get a classical result, either 0 or 1
B. We always get both 0 and 1
C. The qubit disappears from the universe
D. We learn everything about the qubit perfectly
4. Why is measuring a qubit different from reading a classical bit?
A. Measuring a qubit can change its state B. Classical bits cannot be read C. Qubits always give the same answer D. Classical bits are always random
5. What is superposition?
A. A computer being very fast B. A quantum state that combines possibilities C. A broken bit D. A type of programming language
6. Which is a useful beginner picture for a qubit in superposition?
A. A light switch definitely off B. A light switch definitely on C. A spinning coin before it lands D. A printed number on paper
7. What is interference in quantum computing?
A. Noise from a radio B. A computer overheating C. Quantum possibilities strengthening or cancelling each other D. A mistake in binary arithmetic
8. Why is quantum parallelism not enough by itself?
A. Superpositions cannot exist B. Measurement only gives limited information C. Classical computers are always faster D. Qubits cannot be measured
9. How many possible bit strings are there for 3 bits?
A. 3 B. 6 C. 8 D. 9
10. In general, how many possible bit strings are connected with n qubits?
A. n
B. 2n
C. 2^n
D. n^2
11. What is entanglement?
A. A normal wire connection between computers B. A special quantum link between systems C. A way of deleting information D. A type of classical bit
12. Why is entanglement important?
A. It lets us describe every qubit separately B. It is one of the features that makes quantum information different C. It stops measurement happening D. It makes computers use less electricity
13. Which statement is true?
A. Quantum computers solve every problem instantly. B. Quantum computers are just ordinary computers with smaller parts. C. Quantum computers may help with some special problems. D. Quantum computers do not use physics.
14. What is Shor’s algorithm famous for?
A. Searching an unsorted list B. Factoring large numbers efficiently on a quantum computer C. Drawing quantum circuits D. Copying unknown qubits
15. Why is Shor’s algorithm important for security?
A. Some security systems rely on factoring being hard B. It makes passwords unnecessary C. It prevents all hacking D. It makes classical computers stop working
16. What is Grover’s algorithm used for?
A. Searching B. Factoring C. Playing music D. Measuring temperature
17. What kind of speedup does Grover’s algorithm give for unstructured search?
A. No speedup B. Quadratic speedup C. Infinite speedup D. It solves the problem before starting
18. Why might quantum computers be useful for simulating molecules?
A. Molecules are quantum systems B. Molecules are made of classical bits C. Molecules cannot be studied by science D. Molecules are always simple
19. What is decoherence?
A. A quantum computer becoming more powerful B. A loss of quantum behaviour due to the environment C. A way of copying a qubit D. A type of search algorithm
20. Why is quantum error correction surprising?
A. Because quantum computers never make errors B. Because it protects quantum information even though unknown qubits cannot simply be copied C. Because it uses no qubits D. Because it turns quantum computers into classical computers
Short answer questions
21. Bit versus qubit
In one or two sentences, explain the difference between a bit and a qubit.
22. Measurement
Why does measuring a qubit not reveal everything about it?
23. Superposition
Explain superposition using a simple analogy.
24. Interference
Why do quantum algorithms need interference, not just superposition?
25. Entanglement
Explain entanglement in simple words.
26. Quantum computers and hype
Why is it wrong to say, “Quantum computers solve everything instantly”?
27. Shor’s algorithm
Why did Shor’s algorithm make people take quantum computing seriously?
28. Grover’s algorithm
Grover’s algorithm gives a speedup for search. Why is this useful but not magical?
29. Quantum simulation
Why is simulating quantum systems a natural job for quantum computers?
30. Building quantum computers
Give one reason why quantum computers are difficult to build.
Answer key
Multiple choice answers
| Question | Answer |
|---|---|
| 1 | B |
| 2 | A |
| 3 | A |
| 4 | A |
| 5 | B |
| 6 | C |
| 7 | C |
| 8 | B |
| 9 | C |
| 10 | C |
| 11 | B |
| 12 | B |
| 13 | C |
| 14 | B |
| 15 | A |
| 16 | A |
| 17 | B |
| 18 | A |
| 19 | B |
| 20 | B |
Short answer guidance
21. Bit versus qubit
A bit is classical and is either 0 or 1. A qubit is quantum and can be in states that are not simply 0 or 1 before measurement.
22. Measurement
Measurement gives only one classical result, such as 0 or 1, and usually changes the qubit’s state.
23. Superposition
A common analogy is a spinning coin before it lands. It is not definitely heads or tails in the ordinary sense until it is observed.
24. Interference
Superposition gives many possible paths, but interference is needed to make wrong answers cancel and useful answers become more likely.
25. Entanglement
Entanglement is a special quantum connection where two or more quantum systems share a joint state that cannot be explained by describing each part separately.
26. Quantum computers and hype
Quantum computers only give advantages for some types of problems. Measurement limits what information can be extracted, and not all problems have useful quantum algorithms.
27. Shor’s algorithm
It showed that a quantum computer could factor large numbers efficiently, which matters because some security systems rely on factoring being hard for classical computers.
28. Grover’s algorithm
It gives a quadratic speedup, which can be very useful for large searches, but it does not make search instant.
29. Quantum simulation
Quantum systems are hard for classical computers to simulate, so using a quantum system to simulate another quantum system is a natural idea.
30. Building quantum computers
Quantum systems are fragile. They can lose their quantum behaviour through decoherence, and unknown qubits cannot simply be copied for easy error correction.