ket.quantumstate

Quantum state snapshot.

This module provides the base class for a snapshot of a quantum state obtained using a quantum simulator.

Classes ket.quantumstate

QuantumState

Snapshot of a quantum state.
class QuantumState(qubits: Quant)

Snapshot of a quantum state.

This class holds a reference for a snapshot of a quantum state obtained using a quantum simulator. The result may not be available right after the measurement call, especially in batch execution.

You can instantiate this class by calling the dump function.

Example:
from ket import *

p = Process()
a, b = p.alloc(2)
with around(cat(kron(H, I), CNOT), a, b):
    Y(a)
    inside = dump(a+b)

outside = dump(a+b)
print(inside.show())
# |01⟩    (50.00%)
#  -0.707107i     ≅     -i/√2
# |10⟩    (50.00%)
#  0.707107i     ≅      i/√2

print(outside.show())
# |11⟩    (100.00%)
#  -1.000000i     ≅     -i/√1
Parameters:

qubits – Qubits from which to capture a quantum state snapshot.

property states: dict[int, complex] | None

Get the quantum state.

Returns a dictionary mapping base states to their corresponding probability amplitudes.

Returns:

The quantum state, or None if the quantum state information is not available.

get() → dict[int, complex]

Get the quantum state.

If the quantum state is not available, the quantum process will execute to get the result.

property probabilities: dict[int, float] | None

Get the measurement probabilities.

Returns a dictionary mapping base states to their corresponding measurement probabilities.

Returns:

The measurement probabilities, or None if the quantum state information is not available.

sample(shots=4096, seed=None) → dict[int, int] | None

Get the quantum execution shots.

The parameters shots and seed are used to generate the sample from the quantum state snapshot.

Parameters:

  • shots – Number of shots. Defaults to 4096.

  • seed – Seed for the RNG.

Returns:

A dictionary mapping measurement outcomes to their frequencies in the generated sample, or None if the quantum state information is not available.

sphere() → Figure

Generate a Bloch sphere plot representing the quantum state.

This method creates a Bloch sphere plot visualizing of one qubit quantum state.

Note

This method requires additional dependencies from ket-lang[visualization].

Install with: pip install ket-lang[visualization].

Returns:

A Bloch sphere plot illustrating the quantum state.

show(format_str: str | None = None, mode: Literal['latex', 'str'] | None = None) → str | Math

Return the quantum state as a string.

Use the format string to change the print format of the basis states:

  • i: print the state in the decimal base

  • b: print the state in the binary base (default)

  • i|b<n>: separate the n first qubits; the remaining print in the binary base

  • i|b<n1>:i|b<n2>[:i|b<n3>...]: separate the n1, n2, n3, ... first qubits

Example:
from ket import *

p = Process()

q = p.alloc(19)
X(ctrl(H(q[0]), X, q[1:])[1::2])
d = dump(q)

print(d.show('i'))
# |87381⟩ (50.00%)
#  0.707107               ≅      1/√2
# |436906⟩        (50.00%)
#  0.707107               ≅      1/√2
print(d.show('b'))
# |0010101010101010101⟩   (50.00%)
#  0.707107               ≅      1/√2
# |1101010101010101010⟩   (50.00%)
#  0.707107               ≅      1/√2
print(d.show('i4'))
# |2⟩|101010101010101⟩    (50.00%)
#  0.707107               ≅      1/√2
# |13⟩|010101010101010⟩   (50.00%)
#  0.707107               ≅      1/√2
print(d.show('b5:i4'))
# |00101⟩|5⟩|0101010101⟩  (50.00%)
#  0.707107               ≅      1/√2
# |11010⟩|10⟩|1010101010⟩ (50.00%)
#  0.707107               ≅      1/√2
Parameters:

  • format – Format string that matches (i|b)\d*(:(i|b)\d+)*.

  • mode – If "str", return a string representation of the quantum state. If "latex", return a LaTeX Math representation of the quantum state. If in Jupyter Notebook, defaults to "latex", otherwise defaults to "str".

Returns:

The formatted quantum state as a string, or Latex Math.

histogram() → Figure

Generate a histogram representing the quantum state.

This method creates a histogram visualizing the probability distribution of the quantum state.

Note

This method requires additional dependencies from ket-lang[visualization].

Install with: pip install ket-lang[visualization].

Returns:

Histogram of the quantum state.