Examples

Each example is a complete program. Copy it, run it, and you will see the output shown under it: every output on this page was produced by running the code with qsengine 1.1.1.

Bell state
Exact amplitudes
Rotation
Bad input

Bell state

Two qubits put into an entangled state, then measured 1000 times.

import qsengine

qc = qsengine.QuantumCircuit(2)
qc.h(0)
qc.cx(0, 1)

counts = qc.run(shots=1000, seed=1)
print(counts)

Output

{'00': 513, '11': 487}

00: 513
01: 0
10: 0
11: 487

Only 00 and 11 appear: the two qubits always agree.

Exact amplitudes

A three-qubit GHZ state read exactly, without sampling.

import qsengine

qc = qsengine.QuantumCircuit(3)
qc.h(0)
qc.cx(0, 1)
qc.cx(1, 2)

print(qc.probabilities())
print(qc.statevector())

Output

[0.5 0.  0.  0.  0.  0.  0.  0.5]
[0.70710678+0.j 0.        +0.j 0.        +0.j 0.        +0.j
 0.        +0.j 0.        +0.j 0.        +0.j 0.70710678+0.j]

000: 0.5
001: 0
010: 0
011: 0
100: 0
101: 0
110: 0
111: 0.5

The exact probability of each of the 8 basis states.

Rotation

One qubit rotated by π/3 about the Y axis.

import math
import qsengine

qc = qsengine.QuantumCircuit(1)
qc.ry(0, math.pi / 3)

print(qc.probabilities())
print(qc.run(shots=1000, seed=7))

Output

[0.75 0.25]
{'1': 257, '0': 743}

0: 743
1: 257

cos²(π/6) = 0.75, and 743 of 1000 shots measured 0.

Bad input

Mistakes raise a plain Python ValueError on the line that made them.

import qsengine

qc = qsengine.QuantumCircuit(2)
qc.cx(1, 1)

Output

Traceback (most recent call last):
  File "example.py", line 4, in <module>
    qc.cx(1, 1)
ValueError: qubit 1 used more than once in one gate

The gate is not recorded, so the circuit stays valid.