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AFAIK, $n$ qubits together can be described by using a column vector (also called State vector) of $2^n$ complex amplitudes such that sum of the squares of mod of all these complex amplitudes will be $1$.

However, as per below snippet for qsphere visualisation, what does the spikes of different colours denote?

from qiskit.quantum_info import random_statevector
from qiskit.visualization import plot_state_qsphere
num_qb = 3
my_sv = random_statevector(2**num_qb)  
plot_state_qsphere(my_sv)

qsphere of 3 qubit

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  • $\begingroup$ This video nicely explains it all. $\endgroup$
    – RSW
    Oct 5, 2022 at 11:14

1 Answer 1

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The size of the points on the spike shows the probability of the state and the color represents the phase of the state , for example state $|000\rangle$ is blue so it has a phase of 0 and the point is larger that the rest of them so it has the highest probability. state $|110\rangle$ is the second largest to it, so it has the second largest probability, and it is green so its phase is in pi to 3*pi/2 range. you can check here and here for more information about qsphere

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    $\begingroup$ One correction - the size of the points implies upon the probability amplitudes of each computational basis states. The color implies upon the phase of each amplitude. The term “probability” refers to the magnitude squared of the probability amplitude. $\endgroup$
    – Ohad
    Aug 15, 2022 at 8:29

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