Cirq Quantum Computing Framework

1.6.1 · active · verified Fri Apr 17

Cirq is an open-source Python framework developed by Google for creating, editing, and invoking Noisy Intermediate Scale Quantum (NISQ) circuits. It provides tools for designing quantum algorithms and running them on simulators or quantum hardware. Cirq maintains an active release schedule, typically with major updates every 1-2 months, focusing on new features, performance improvements, and compatibility with Google's quantum hardware.

Common errors

```
ModuleNotFoundError: No module named 'cirq.rigetti'
```
cause The `cirq-rigetti` subpackage was removed from Cirq's main distribution in v1.6.0.

fix If you require `cirq-rigetti`, install its last standalone version: `pip install cirq-rigetti==1.5.0`.
```
ModuleNotFoundError: No module named 'cirq_ft'
```
cause The fault-tolerant functionality moved to the separate `qualtran` library.

fix Install the `qualtran` library: `pip install qualtran`. Update your imports to reference `qualtran` instead of `cirq_ft`.
```
Your Python version is 3.10.x but cirq requires >=3.11.0.
```
cause Cirq v1.6.0 and later require a minimum Python version of 3.11.

fix Upgrade your Python environment to 3.11 or newer. Alternatively, install an older compatible Cirq version, e.g., `pip install 'cirq<1.6.0'`.
```
TypeError: 'numpy.ndarray' object is not callable
```
cause Commonly occurs when using an older Cirq version with NumPy 2.x, which changed some array behaviors.

fix Upgrade Cirq to v1.5.0 or newer (`pip install --upgrade cirq`), which added NumPy 2.x compatibility. Or, downgrade NumPy to a version prior to 2.0 (`pip install 'numpy<2.0.0'`).

Warnings

breaking The `cirq-rigetti` subpackage was fully removed from Cirq as of v1.6.0. Attempts to import it from `cirq` will fail.
Fix: For legacy code requiring `cirq-rigetti`, explicitly install `cirq-rigetti==1.5.0`. For new development, use Rigetti's current SDK or relevant integration libraries.
breaking The `cirq-ft` package was removed from Cirq as of v1.4.0, having moved to its own repository under the `qualtran` library. Direct imports will fail.
Fix: Install `qualtran` (`pip install qualtran`) and import functionality from there. Replace `cirq_ft` imports with `qualtran`.
breaking Cirq v1.6.0 and later versions require Python 3.11 or higher.
Fix: Upgrade your Python environment to version 3.11 or newer. If you must use an older Python version, pin Cirq to `<1.6.0`.
gotcha Support for NumPy 2.x was added in Cirq v1.5.0. Older Cirq versions may have compatibility issues or breakages if used with NumPy 2.x.
Fix: Ensure you are using Cirq v1.5.0 or newer when working with NumPy 2.x. If using an older Cirq version, pin NumPy to `<2.0.0`.
gotcha Cirq has undergone significant API stabilization since its v1.0.0 release. Code written for pre-1.0 versions may use deprecated or removed symbols.
Fix: Consult the official Cirq migration guides for updates related to major version changes. Update your code to use the modern v1.x API.

Install

pip install cirq Install latest Cirq

Imports

Circuit
```
import cirq
circuit = cirq.Circuit(...)
```

Simulator

import cirq
simulator = cirq.Simulator()

GridQubit
```
import cirq
q = cirq.GridQubit(0, 0)
```

import cirq
circuit = cirq.Circuit(cirq.H(q))

rigetti
wrong:
```
import cirq.rigetti
```
correct:
```
pip install cirq-rigetti==1.5.0
import cirq_rigetti
```
The `cirq-rigetti` subpackage was removed from the main `cirq` installation in v1.5.0 and fully removed in v1.6.0. It must now be installed separately for legacy access to v1.5.0 functionality, or use newer Rigetti SDKs.
cirq_ft
wrong:
```
import cirq_ft
```
correct:
```
pip install qualtran
import qualtran
```
The `cirq-ft` package was moved from `cirq` to its own repository and is now part of the `qualtran` library. Direct imports from `cirq_ft` will fail in recent Cirq versions.

Quickstart

This quickstart demonstrates how to construct a simple Bell state quantum circuit, print its representation, and then simulate it using Cirq's built-in simulator to obtain measurement results.

import cirq

# Define a qubit
q0 = cirq.GridQubit(0, 0)

# Create a quantum circuit for a Bell state
circuit = cirq.Circuit(
    cirq.H(q0),        # Apply Hadamard gate
    cirq.CNOT(q0, cirq.GridQubit(0, 1)), # Apply CNOT with another qubit
    cirq.measure(q0, cirq.GridQubit(0, 1), key='result') # Measure both qubits
)

print("Circuit:")
print(circuit)

# Simulate the circuit
simulator = cirq.Simulator()
result = simulator.run(circuit, repetitions=100) # Run 100 times

print("\nResults:")
print(result.histogram(key='result')) # Print measurement outcome histogram

view raw JSON →