Quantum Computing Asked by SuFong Chien on June 28, 2021
How do you use the IBM quantum composer to encode some data $(a,b,c,d)$ represented by a vector ket in which $a,b,c,d$ have been normalized to one? $a|00rangle + b|01rangle + c|10rangle + d|11rangle$
One way to do it is to use the initialize function then decomposed the circuit and print out the qasm
code and pull it over to the composer...
There was a similar question to your question here
But here is an example that might help:
from qiskit import QuantumCircuit, IBMQ
import numpy as np
num_qubits = 2
vector = [1,2,3,4] #[a,b,c,d] not normalize
initial_state = vector/np.linalg.norm(vector) #normalize the state
circuit = QuantumCircuit(num_qubits,num_qubits)
circuit.initialize(initial_state, [0,1])
print(circuit)
┌─────────────────────────────────────────────┐
q_0: ┤0 ├
│ initialize(0.18257,0.36515,0.54772,0.7303) │
q_1: ┤1 ├
└─────────────────────────────────────────────┘
c: 2/═══════════════════════════════════════════════
And now you can use the decomposed
function to decomposed this circuit into the gates that is available within the composer:
decomposed_circuit = transpile(circuit, basis_gates=['h', 'x', 'cx', 'ccx', 't', 'tdg', 's', 'sdg', 'p' , 'rz' , 'sx' ,'sxdg','rx', 'ry','rxx' , 'rzz',] )
┌────────────┐┌───┐┌─────────────┐┌───┐
q_0: ┤ RY(2.0344) ├┤ X ├┤ RY(0.17985) ├┤ X ├
├────────────┤└─┬─┘└─────────────┘└─┬─┘
q_1: ┤ RY(2.3005) ├──■───────────────────■──
└────────────┘
c: 2/═══════════════════════════════════════
Extracting the 'qasm' code:
print(decomposed_circuit.qasm())
print(decomposed_circuit.qasm())
OPENQASM 2.0;
include "qelib1.inc";
qreg q[2];
creg c[2];
ry(2.0344439) q[0];
ry(2.300524) q[1];
cx q[1],q[0];
ry(0.1798535) q[0];
cx q[1],q[0];
Now take that and paste it in the QASM
code block in the Circuit Composer
Now you have the initialize state that you wanted in the composer.
Answered by KAJ226 on June 28, 2021
You can implement a method proposed in this article Transformation of quantum states using uniformly controlled rotations. The authors present a method for transforming any quantum state to any other one. Of course, this allow to change initial state $|0rangle^n$ in the composer to arbitrary $n$-qubit. The method works with $CNOT$, $Ry$ and $Rz$ gates only. All these are available in the composer.
According to my knowledge, this method is implemented in Qiskit init
function which proposed KAJ226 in the other answer.
Answered by Martin Vesely on June 28, 2021
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