Stage 4 · Lesson 11 of 17
Quantum simulators and physical hardware
1 · Big question
How is an ideal simulator different from a physical quantum processor?
- Define a simulator as classical software.
- Compare ideal, simplified noisy and physical-hardware paths.
- Explain queues and external hardware access.
- Label example hardware data honestly.
2 · Before we begin
Ideas to bring with you
- Circuit probabilities can be calculated and sampled.
- Physical experiments require recorded settings and context.
3 · New words
Meet the words before we use them
- simulator
- Classical software that calculates or samples a quantum model.
- quantum processing unit (QPU)
- Physical hardware engineered to operate qubits.
- physical qubit
- A particular engineered qubit available on a selected QPU.
4 · Simple explanation
Build one idea at a time
A quantum simulator is ordinary classical software that calculates or samples a quantum model. It is not a physical quantum computer.
A physical qubit is a particular engineered qubit inside a QPU. Here, noise means unwanted changes or uncertainty from a device or its environment. An ideal simulator follows exact mathematics; a simplified noisy simulator adds a stated teaching error model.
A queue is a waiting list of submitted jobs. External QPUs can require an account and place a job in such a queue. Hardware technologies and access rules differ, so the course never invents a live job or promises permanent free access.
Watch it happen
One circuit, three execution paths
Send the same circuit to an ideal simulator, a simplified noisy simulator and a physical-hardware information panel.
Text description of the animation
Three labelled paths separate exact calculated probabilities, a declared simplified noise model and an external physical QPU. The hardware panel shows only clearly labelled example data unless a learner supplies their own record.
- Run the ideal path and record probabilities.
- Adjust the explicitly simplified noise control and compare counts.
- Classify supplied example hardware data and identify what metadata would be needed for a real claim.
Evidence to calculate or record: Each result is labelled prediction, simulation, simplified noise example or physical experiment, with no generated sample presented as a real job.
Predict
Commit to an idea before the reveal
Which path should match exact theory most closely, and which path may require a provider queue?
Choose a prediction to enable the experiment.
Try it
Classify the result source
Run the ideal path and record probabilities.
Make and lock a prediction first.
8 · Observe
What did the result actually show?
Look at the displayed values before reading the explanation. Record a pattern, an exception or something that changed.
The ideal path follows exact model probabilities. The simplified noise path changes with its teaching parameter. The hardware path explains queues and evidence without fabricating a run.
9 · Explain the result
Connect the evidence to the idea
Simulation tests a model on a classical computer. Physical execution tests a real device under stated conditions; agreement or disagreement must be interpreted with shot variation and noise in mind.
10 · Model and limitation
Useful model, honest boundary
The three paths make the evidence source impossible to confuse.
The simplified noise slider is not a complete model of any named processor, and example hardware counts are not live results.
11 · Common mix-ups
Careful wording prevents big mistakes
A simulator is a hidden physical QPU.
It is classical software implementing a quantum model.
All quantum computers use the same physical technology.
Different platforms engineer qubits in different ways.
Generated random counts can be labelled as an IBM job.
Only an actual provider job record may be described that way.
12 · Real quantum-computing connection
Where this appears in circuit work
Learners usually develop and check a small circuit in a simulator before submitting an adapted circuit to external hardware.
13 · Show me moreOptional deeper explanation
Show me more
State-vector simulation cost grows rapidly with qubit count. Small classroom circuits are easy to simulate, which is useful but does not make the simulator a QPU.
Try this
Explain the deeper idea in your own words, including one limitation.
14 · Quick summary
Keep these ideas
- Simulators are classical software.
- Ideal, simplified noisy and physical results are different evidence types.
- External hardware can involve accounts and queues.
- Example data must never be presented as a live job.
Ten-question quiz
Check the ideas—not decorative details
Feedback appears after submission. Retry whenever you like; 8/10 or above means “Topic understood”.
Sources and accuracy notes3 checked references · reviewed 2026-08-15
These records identify the claim each source supports. External documentation can change; dated platform claims were checked on the shown access date.
- Exact and noisy simulation with Qiskit Aer primitivesIBM Quantum · Exact simulation, noise models and sampled results · accessed 2026-08-15
Supports quiz questions ql-11-q-01, ql-11-q-02, ql-11-q-06, ql-11-q-08, ql-11-q-10 and their related lesson explanations about distinguishing exact simulation from noisy simulation; simulators as classical software; limits of comparing a noise model with physical hardware.
- IBM Quantum ComposerIBM Quantum · What it is, interface tour, simulation and QPU execution · accessed 2026-08-15
Supports quiz questions ql-11-q-03, ql-11-q-04, ql-11-q-05, ql-11-q-07 and their related lesson explanations about visual circuit construction in IBM Quantum Composer; simulation before quantum-hardware execution; sign-in and external-account boundary.
- Quantum information scienceNational Institute of Standards and Technology · Quantum information science overview · accessed 2026-08-02
Supports quiz questions ql-11-q-09 and their related lesson explanations about quantum information science; quantum computing, sensing and communication; measurement science and standards.
- This model is deliberately limited: The simplified noise slider is not a complete model of any named processor, and example hardware counts are not live results.
- Predictions, simulations and physical-hardware evidence are labelled separately.