cirq

Cirq - Quantum Computing with Python

Cirq is Google Quantum AI's open-source framework for designing, simulating, and running quantum circuits on quantum computers and simulators.

When to Use This Skill

Use this skill when:

• Building, simulating, or optimizing NISQ circuits in Python
• Running jobs on Google Quantum AI processors (via cirq-google) or partner backends (IonQ, Azure Quantum, AQT, Pasqal)
• Modeling noise, compiling to hardware gatesets, or designing characterization experiments
• Using parameter sweeps, transformers, or the ReCirq experiment patterns

For IBM hardware use qiskit; for quantum ML with autodiff use pennylane; for physics simulations use qutip.

Installation

Requires Python 3.11+. Current stable release: 1.6.1 (August 2025). Vendor packages share the same version number.

uv pip install "cirq==1.6.1"

For hardware integration (pin matching versions for reproducibility):

# Google Quantum Engine (requires approved GCP project access)
uv pip install "cirq-google==1.6.1"

# IonQ
uv pip install "cirq-ionq==1.6.1"

# AQT (Alpine Quantum Technologies)
uv pip install "cirq-aqt==1.6.1"

# Pasqal
uv pip install "cirq-pasqal==1.6.1"

# Azure Quantum (IonQ, Honeywell/Quantinuum backends)
uv pip install "azure-quantum[cirq]"

For latest features during development, omit version pins; for production or hardware runs, pin all packages to the same Cirq release.

Quick Start

Basic Circuit

import cirq
import numpy as np

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

# Build circuit
circuit = cirq.Circuit(
    cirq.H(q0),              # Hadamard on q0
    cirq.CNOT(q0, q1),       # CNOT with q0 control, q1 target
    cirq.measure(q0, q1, key='result')
)

print(circuit)

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

# Display results
print(result.histogram(key='result'))

Parameterized Circuit

import sympy

# Define symbolic parameter
theta = sympy.Symbol('theta')

# Create parameterized circuit
circuit = cirq.Circuit(
    cirq.ry(theta)(q0),
    cirq.measure(q0, key='m')
)

# Sweep over parameter values
sweep = cirq.Linspace('theta', start=0, stop=2*np.pi, length=20)
results = simulator.run_sweep(circuit, params=sweep, repetitions=1000)

# Process results
for params, result in zip(sweep, results):
    theta_val = params['theta']
    counts = result.histogram(key='m')
    print(f"θ={theta_val:.2f}: {counts}")