QuantumRegister.js

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QuantumRegister.js gates.js helper.js index.js

QuantumRegister.js

const math = require('mathjs');
const weighted = require('weighted');
const gates = require('./gates');

class Register {

¶

This is the constructor for the Register, it takes a parameter numQubits which is the number of Qubits in the register
```
	constructor(numQubits) {
		this.numQubits = numQubits;
```
¶

The number of amplitudes needed is 2^n, Where N is the number of qubits. The math.zeros function Creates a matrix of 0s, ie. math.zeros(5) = [0, 0, 0, 0, 0]
```
		this.amplitudes = math.matrix([math
			.zeros(math.pow(2, numQubits))
			.toArray()], 'sparse');
```

Set the chance of getting all Zeros to 1

		this.amplitudes = math.subset(this.amplitudes, math.index(0, 0), 1);

¶

Set the fact it has not been measured
```
		this.measured = false;
	}
```
¶

Apply a gate to the register. The parameters, gate is a string with the name of the gate from the gates class. qubit1 is the place in the register of the qubit the gate is being applied to. qubit2 is, if a CNOT Gate is being used, its the target qubit, and qubit1 is the control.
```
	applyGate(gate, qubit1, qubit2 = -1) {
		if (this.measured) {
```
¶

If it has already been measured, then you cannot apply a gate, so an Error will be thrown
```
			throw new Error('Cannot Apply Gate to a Measured Quantum Register');
		} else {
```

Get the gate from the generateGates function, and then multiply the amplitude vector against it

			const gateMatrix = gates.generateGate(gate,
				this.numQubits,
				qubit1,
				qubit2);

			this.amplitudes = math.multiply(this.amplitudes, gateMatrix);
		}
	}

¶

Measure the qubit register
```
	measure() {
```
¶

If it has already been measured, just return that value
```
		if (this.measured) {
			return this.value;
		}
```

Get a list of probabilities by squaring the absolute value of the amplitudes.

		let probabilities = [];
		math.forEach(this.amplitudes, (val) => {
			let probability = math.pow(math.abs(val), 2);
			probabilities.push(probability);
		});

¶

Choose an item by making a list of numbers 0 to the length of the probabilities array. Then, use the probabilities array as the weights for the picker.
```
		let results = math
			.zeros(probabilities.length)
			.toArray()
			.map((val, index) => index);
```

Convert to Binary, add extra 0’s if needed.

		this.value = Number(weighted.select(results, probabilities)).toString(2);

		if (this.value.length < this.numQubits) {
			this.value = '0'.repeat(this.numQubits - this.value.length) + this.value;
		}

		this.measured = true;
		return this.value;
	}
}

module.exports = Register;