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Gates

Drag onto a wire, or click a gate then click a cell. Arrow keys move the cursor, Enter places, Delete removes.
Qubits
Backend
Load
—
after all gates
browser engine Press Run to execute on the selected backend.
Bars are sampled counts from 1024 shots · red tick marks the exact probability. The gap between them is shot noise — the same thing you see on real hardware.
Basis states read left to right as q0 q1 q2 … (top wire first). Colour encodes phase: invisible in the histogram, and exactly what interference acts on.
An arrow shorter than the sphere means that qubit is entangled — it has no state of its own, only the group does.
Editable when the target is Qiskit — edit the code and the circuit above updates to match about half a second after you stop typing, or press Run to execute exactly what's here. Other frameworks stay read-only: this editor understands a restricted Qiskit subset, not five languages at once. 

            

              This is the exact context a language model would receive. Nothing else is
              sent. Every number in it was computed by the simulator, and the verifier
              rejects any answer that adds one.
            

            

          

        

      


      

        
Tutor grounded

        

        

          Every statement above is computed from your circuit and its state vector.
          A language model would write the prose from these same facts and still pass
          through the verifier, so it can never invent a result.
        

      


    

  


  
  

    

      
Modules

      

        New here? Begin with the Starter Trail — a few short steps where you do something with your hands in the first minute. Every module after that climbs the same six rungs: something you already know, then the new idea as a picture, and only then the symbols. No equation appears before the diagram that gives it meaning. The maths chapters are a Toolkit: open them only when a step asks for a refresher.
      

    

    

    
  


  
  

    

      Interference lab
      
Drag one dial and watch an outcome cancel

      

        This is the whole of quantum computing in one control. Two routes reach each
        outcome; the dial sets the phase between them. Turn it to π and the two arrows
        to |0⟩ point in opposite directions, add to nothing, and that outcome stops
        happening entirely. Everything on screen is computed by the same engine that
        runs your circuits.
      

    

    

    

      
Why this matters

      

        A classical probabilistic bit has no phase, so nothing you can do to it will make
        two routes to the same outcome cancel. That single difference — not "trying every
        answer at once" — is where quantum speedup comes from.
      

    

  


  
  

    
Practise

    
Each puzzle checks the circuit you build by running it. Many different circuits can work, and using fewer gates scores higher. There is nothing to memorise, and you can try again as often as you like.


    

      
      

        
Circuit challenges · circuit golf

        
Build a circuit that produces a target distribution.

        
We run your circuit to check it. Fewer gates scores higher.

      

    

    


    

      
      

        
Coding challenges

        
Write or fix real Qiskit code in the editor.

        
We run your code to check it.

      

    

    


    

      
      

        
Put it in order

        
Arrange the gates in the correct sequence.

        
We build your order into a real circuit and run it to check.

      

    

    


    

      
      

        
Steer the Bloch vector

        
Add gates and watch the arrow move toward the target ring.

        
We check how close the arrow lands to the target.

      

    

    


    

      
      

        
Fill in the code

        
Complete the missing line of code.

        
We run it to check. More than one answer can work.

      

    

    


    

      
      

        
Concept check

        
Answer a multiple-choice question about a concept.

        
A wrong pick is just a step: each one shows you a common idea and why it is not quite right.

      

    

    

  


  
  

    
Your progress

    
Each concept has a score from 0 to 100 that moves a little after every answer you give. It shows where you are right now, not a grade. A concept you have not started just says "Not started yet".


    


    
My certificates

    


    
Due for review

    
Ideas fade a little if you do not visit them for a while. These are ones you had got right, ready for a quick refresh.

    


    
Concept map

    
Every concept in the course, drawn as a map. Faded ones open up as you work through the ones they build on.

    

    

    


    
Mastery by concept

    


    
Session

    

    
  


  
  

    
Instructor view

    

      One class, 24 students, six concepts. You appear in the roster live —
      the row marked "You" reads the same mastery scores the learner view writes. The
      other 23 are sample data, generated from a fixed seed so the class is stable.
    

    

    


    
Concept bottlenecks

    

      How many students are below Working on each concept — click a row to see the count.
    

    


    

      

      

         Mastered · 80–100
         Working · 55–79
         Shaky · 45–54
         Weak · below 45
        Click a name to drill in.
      

    

    


    
Misconceptions across the class