Quantum Operations¶

Measurement¶

Measurement of a register in QCGPU doesn’t collapse the state (although this may be added in the future). When you measure the state, you can specify the number of times to sample. The output of this measure function is a dictionary with the bitstrings of the outputs, along with the number of times they were measured.

You can measure a register as follows,

import qcgpu

register = qcgpu.State(5)

register.measure(samples=1000)
# {'00000': 1000}

There is also a convenience method to measure only a single qubit. Again, the state is not collapsed

import qcgpu

register = qcgpu.State(5)

register.h(0)

register.measure_qubit(0, samples=1000)
# {'1': 523, '0': 477}

Probability¶

QCGPU provides another method for getting the probability of each outcome.

The probability of getting an outcome $j$ from a state $\lvert \psi \rangle = \sum_{j = 0}^{2^n - 1} \alpha_j \lvert j \rangle$ is

The method probabilities returns a numpy array with each of the values corresponding to $\lvert \alpha_j \lvert ^2$ for each index $j$.

import qcgpu

register = qcgpu.State(1)
register.h(0)

register.probabilities() # [0.5, 0.5]

This method is particularly useful to plot the probabilities of each outcome.