Hadamard Gate's probability

[icepolarizer]

I'm not sure I'm using this correctly, but I think there is some problem in hadamard gate. When I apply hadamard gate to every qubits and run them, they are mostly zero.

var qubitSystem = new QuantumCircuit(10);
qubitSystem.addGate("h", 1, [0,1,2,3,4,5,6,7,8,9]);
qubitSystem.run();
console.log(qubitSystem.measureAll());

This mostly returns zero-filled list. I know this is just a simulator, but I'm using this for my project, which includes some sort of Quantum Randint Generator. Could you please consider changing some probabilities of hadamard gate, when I measure them?

[perak]

Hi @kenixer

Problem is that you cannot add single-qubit gate to multiple wires in the same command, so you are not using it correctly.

Correct code would be:

var qubitSystem = new QuantumCircuit(10);
qubitSystem.addGate("h", -1, 0);
qubitSystem.addGate("h", -1, 1);
qubitSystem.addGate("h", -1, 2);
qubitSystem.addGate("h", -1, 3);
qubitSystem.addGate("h", -1, 4);
qubitSystem.addGate("h", -1, 5);
qubitSystem.addGate("h", -1, 6);
qubitSystem.addGate("h", -1, 7);
qubitSystem.addGate("h", -1, 8);
qubitSystem.addGate("h", -1, 9);
qubitSystem.run();
console.log(qubitSystem.measureAll());

(or even better - make a loop :) )

You can also try https://quantum-circuit.com - it uses this library and there is visual drag & drop editor.

[perak]

With loop:

var qubitSystem = new QuantumCircuit(10);

for(var i = 0; i < qubitSystem.numQubits; i++) {
    qubitSystem.addGate("h", -1, i);
}

qubitSystem.run();
console.log(qubitSystem.measureAll());

[perak]

-1 means "Add gate to the end of the wire".

You can also export circuit to svg picture and see what you've made (see docs).

[perak]

By the way, if you need random number generator, best way is to measure and store measurement into classical register, so you can directly access random integer without gymnastics, like this:

var quantumRandom = function() {
    var qubitSystem = new QuantumCircuit(10);

    for(var i = 0; i < qubitSystem.numQubits; i++) {
        // add Hadamard gate to i-th wire
        qubitSystem.addGate("h", -1, i);
        // add measurement gate to i-th qubit which will store result into classical register "C", into i-th classical bit
        qubitSystem.addMeasure(i, "c", i); 
    }

    qubitSystem.run();

    return qubitSystem.getCregValue("c");
};

// Usage
console.log(quantumRandom());

[icepolarizer]

Thanks. It helped me REALLY LOT. Thanks for making this great library. :1st_place_medal: