Cirq

1.6.1 · active · verified Tue Apr 14

Cirq is a Python framework developed by Google's Quantum AI team for creating, editing, and invoking Noisy Intermediate Scale Quantum (NISQ) circuits. It focuses on providing fine-tuned control over quantum circuits and gate-level operations for current-generation quantum processors. The library is actively maintained, with frequent releases, and is currently at version 1.6.1.

Warnings

breaking The minimum required Python version has been increased to 3.11.0. Older Python versions are no longer supported.
Fix: Upgrade your Python environment to 3.11.0 or later. Consider using a virtual environment (e.g., `python -m venv .venv`).
breaking The `cirq-rigetti` subpackage has been completely removed from the main `cirq` distribution. It was previously deprecated in v1.5.0.
Fix: For legacy code requiring `cirq-rigetti` functionality, use the last standalone release `cirq-rigetti-1.5.0`. Alternatively, migrate to other supported hardware integrations or the standalone `pyquil` library.
breaking The `cirq-ft` package (for fault-tolerant resource estimation) was removed from Cirq. It was deprecated in v1.3.0.
Fix: The functionality of `cirq-ft` has been moved to the `Qualtran` repository. Users should now use the `Qualtran` library for fault-tolerant resource estimation needs.
deprecated The `cirq-rigetti` subpackage was deprecated and became an opt-in component, requiring explicit installation.
Fix: If still using Cirq versions <1.6.0 and needing Rigetti integration, install it explicitly via `pip install cirq-rigetti`. For versions >=1.6.0, refer to the breaking change above.
gotcha A bug in `cirq.kraus` could return erroneous near-zero matrices, potentially affecting simulations or analysis involving Kraus operators.
Fix: Upgrade to Cirq v1.6.1 or later to get the fix for the `cirq.kraus` bug.
gotcha While Cirq v1.0.0 brought a commitment to API stability following SemVer, earlier versions (pre-1.0) were in an 'alpha' state with frequent breaking changes between releases.
Fix: When working with older Cirq codebases, it is crucial to pin to specific minor versions (`cirq==0.X.Y`) and be prepared for migrations if upgrading to newer major versions. For current development, rely on the stated SemVer compatibility.

Install

pip install cirq Recommended (includes core + optional modules)
pip install cirq-core Core module only

Imports

cirq
```
import cirq
```
The main top-level package for all core functionalities.
LineQubit
```
import cirq
# ...
q0, q1 = cirq.LineQubit.range(2)
```
Many common classes and functions are exposed directly under the `cirq` namespace for convenience, avoiding deeper module imports.
Simulator
```
import cirq
# ...
simulator = cirq.Simulator()
```
Simulators are often accessed directly via `cirq.Simulator`.

Quickstart

This quickstart demonstrates how to build a basic quantum circuit, simulate it using Cirq's built-in simulator, and retrieve measurement results as a histogram. It creates a Bell state using Hadamard and CNOT gates and then measures both qubits.

import cirq
import numpy as np

# Create two qubits
q0, q1 = cirq.LineQubit.range(2)

# Build a simple Bell state circuit
circuit = cirq.Circuit(
    cirq.H(q0),
    cirq.CNOT(q0, q1),
    cirq.measure(q0, q1, key='result')
)

print("Circuit:")
print(circuit)

# Simulate the circuit 1000 times
simulator = cirq.Simulator()
result = simulator.run(circuit, repetitions=1000)

# Display the measurement results
print("\nMeasurement results (histogram):")
print(result.histogram(key='result'))

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