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Suppose that I have a 5 qubit quantum computer and want to generate

  1. 4 entangled states (each of 5 qubits)
  2. Single 6 qubit entangled state.

Are these 2 cases possible? I am a beginner please help!

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    $\begingroup$ 1. You can create an entangled state that involves all available 5 qubits. You can sequentially (one after the other) create 4 entangled states involving 5 qubits each. But you cannot create 4 entangled states, each involving 5 qubits, simultaniously. 2. No you cannot create an entangled state involving 6 qubits, since you only have 5 qubits available. $\endgroup$ Feb 12, 2020 at 14:13
  • $\begingroup$ @BrunoRijsman Here specification says it is a 5 qubit QC. Sequentially (one after the other) can I create 4 entangled states involving 5 qubits each? this is conflicting with the Amir Ebrahimi answer. Can you confirm? $\endgroup$ Feb 13, 2020 at 4:26

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To go straight to your questions:

  1. No, simply because if you want four 5-qubit entangled states you'd need 20 qubits.
  2. No, if you only have 5 qubits, then you wouldn't be able to create a 6-qubit entangled state. You'd need 6 qubits in order to do that.

One way I can think of creating a 5-qubit entangled state is to have one qubit in superposition with a Hadamard gate and then a CNOT from that qubit to the other four qubits. If you wanted 4 of those 5-qubit entangled states, then you'd just repeat that for the other 15 qubits in groups of 5. Here's an example in the circuit composer from IBM's Quantum Experience:

5-qubit entanglement example

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  • $\begingroup$ Please confirm if the argument about case 1 is correct by a reference. As per ur argument u want to say that after creating first 5 qubit entangled state can’t we generate one more? $\endgroup$ Feb 16, 2020 at 6:58
  • $\begingroup$ If you want a second state of entangled qubits after the first one that is generated you will need another set of qubits to create that state if the first one is to also exist at the same time. If you're thinking of reusing qubits from a previously entangled state, then if you can reset them to the ground state, then I suppose you could re-entangle them. I'm not sure I understand what you are going for with these states though. $\endgroup$ Feb 17, 2020 at 21:48

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