Learn Cirq - 10 Code Examples & CST Typing Practice Test

Cirq is an open-source Python framework for quantum computing, developed by Google, focused on designing, simulating, and running quantum circuits on NISQ (Noisy Intermediate-Scale Quantum) devices.

View all 10 Cirq code examples →

Cirq Simple Quantum Circuit Cirq Single Qubit Rotation Cirq Bell State Cirq GHZ State Cirq Random Circuit Cirq Quantum Fourier Transform Cirq Parameterized Gate Cirq Controlled Gates Cirq Swap Gate Example Cirq Measurement in Different Basis

Learn CIRQ with Real Code Examples

Updated Nov 25, 2025

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Code Sample Descriptions

Cirq Simple Quantum Circuit

import cirq

qubits = [cirq.GridQubit(0,0), cirq.GridQubit(0,1)]

circuit = cirq.Circuit()
circuit.append(cirq.H(qubits[0]))
circuit.append(cirq.CNOT(qubits[0],qubits[1]))
circuit.append(cirq.measure(*qubits,key='result'))

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

A minimal Cirq example creating a 2-qubit quantum circuit, applying Hadamard and CNOT gates, and simulating measurements.

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Cirq Single Qubit Rotation

import cirq

q = cirq.GridQubit(0,0)
circuit = cirq.Circuit(cirq.rx(1.5708)(q), cirq.measure(q,key='m'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Applies a rotation gate to a single qubit and measures it.

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Cirq Bell State

import cirq

q0,q1 = cirq.GridQubit(0,0),cirq.GridQubit(0,1)
circuit = cirq.Circuit(cirq.H(q0), cirq.CNOT(q0,q1), cirq.measure(q0,q1,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=1000)
print(result)

Generates a Bell state and measures both qubits.

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Cirq GHZ State

import cirq

q = [cirq.GridQubit(0,i) for i in range(3)]
circuit = cirq.Circuit(cirq.H(q[0]), cirq.CNOT(q[0],q[1]), cirq.CNOT(q[0],q[2]), cirq.measure(*q,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=1000)
print(result)

Creates a 3-qubit GHZ state and measures all qubits.

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Cirq Random Circuit

import cirq

q = [cirq.GridQubit(0,0),cirq.GridQubit(0,1)]
circuit = cirq.testing.random_circuit(qubits=q, n_moments=5, op_density=0.5)
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(circuit)
print(result)

Creates a random quantum circuit with 2 qubits.

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Cirq Quantum Fourier Transform

import cirq

q = [cirq.GridQubit(0,i) for i in range(3)]
circuit = cirq.Circuit()
for i in range(3):
    circuit.append(cirq.H(q[i]))
    for j in range(i+1,3):
        circuit.append(cirq.CZ(q[j],q[i])**(1/2**(j-i)))
circuit.append(cirq.measure(*q,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Implements QFT on 3 qubits.

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Cirq Parameterized Gate

import cirq
import sympy

q = cirq.GridQubit(0,0)
theta = sympy.Symbol('theta')
circuit = cirq.Circuit(cirq.rx(theta)(q), cirq.measure(q,key='m'))
sim = cirq.Simulator()
result = sim.run(circuit,{theta:1.57},repetitions=500)
print(result)

Uses a parameterized rotation gate on a qubit.

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Cirq Controlled Gates

import cirq

q0,q1 = cirq.GridQubit(0,0),cirq.GridQubit(0,1)
circuit = cirq.Circuit(cirq.H(q0), cirq.CZ(q0,q1), cirq.measure(q0,q1,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Demonstrates a controlled-Z gate between two qubits.

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Cirq Swap Gate Example

import cirq

q0,q1 = cirq.GridQubit(0,0),cirq.GridQubit(0,1)
circuit = cirq.Circuit(cirq.SWAP(q0,q1), cirq.measure(q0,q1,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Swaps two qubits and measures them.

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Cirq Measurement in Different Basis

import cirq

q = cirq.GridQubit(0,0)
circuit = cirq.Circuit(cirq.H(q), cirq.measure(q,key='X_basis'), cirq.measure(q,key='Z_basis'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Measures a qubit in X and Z bases.

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Frequently Asked Questions about Cirq

What is Cirq?

Cirq is an open-source Python framework for quantum computing, developed by Google, focused on designing, simulating, and running quantum circuits on NISQ (Noisy Intermediate-Scale Quantum) devices.

What are the primary use cases for Cirq?

Designing and simulating quantum circuits. Running algorithms on Google's quantum processors. Optimization and combinatorial problem solving. Quantum machine learning experiments. Noise-aware quantum algorithm development

What are the strengths of Cirq?

Strong support for NISQ device experimentation. Flexible and modular for custom gate definitions. Noise simulation and calibration tools. Open-source and well-documented. Supported by Google Research and growing community

What are the limitations of Cirq?

Primarily optimized for Google quantum hardware. Steeper learning curve for beginners compared to high-level frameworks. Limited pre-built algorithm libraries compared to Qiskit. Hardware availability constrained to Google's quantum processors. Classical simulation of large circuits is exponentially costly

How can I practice Cirq typing speed?

CodeSpeedTest offers 10+ real Cirq code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.

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Code Sample Descriptions

Cirq Simple Quantum Circuit

import cirq

qubits = [cirq.GridQubit(0,0), cirq.GridQubit(0,1)]

circuit = cirq.Circuit()
circuit.append(cirq.H(qubits[0]))
circuit.append(cirq.CNOT(qubits[0],qubits[1]))
circuit.append(cirq.measure(*qubits,key='result'))

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

A minimal Cirq example creating a 2-qubit quantum circuit, applying Hadamard and CNOT gates, and simulating measurements.

Let’s Try →

Cirq Single Qubit Rotation

import cirq

q = cirq.GridQubit(0,0)
circuit = cirq.Circuit(cirq.rx(1.5708)(q), cirq.measure(q,key='m'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Applies a rotation gate to a single qubit and measures it.

Let’s Try →

Cirq Bell State

import cirq

q0,q1 = cirq.GridQubit(0,0),cirq.GridQubit(0,1)
circuit = cirq.Circuit(cirq.H(q0), cirq.CNOT(q0,q1), cirq.measure(q0,q1,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=1000)
print(result)

Generates a Bell state and measures both qubits.

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Cirq GHZ State

import cirq

q = [cirq.GridQubit(0,i) for i in range(3)]
circuit = cirq.Circuit(cirq.H(q[0]), cirq.CNOT(q[0],q[1]), cirq.CNOT(q[0],q[2]), cirq.measure(*q,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=1000)
print(result)

Creates a 3-qubit GHZ state and measures all qubits.

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Cirq Random Circuit

import cirq

q = [cirq.GridQubit(0,0),cirq.GridQubit(0,1)]
circuit = cirq.testing.random_circuit(qubits=q, n_moments=5, op_density=0.5)
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(circuit)
print(result)

Creates a random quantum circuit with 2 qubits.

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Cirq Quantum Fourier Transform

import cirq

q = [cirq.GridQubit(0,i) for i in range(3)]
circuit = cirq.Circuit()
for i in range(3):
    circuit.append(cirq.H(q[i]))
    for j in range(i+1,3):
        circuit.append(cirq.CZ(q[j],q[i])**(1/2**(j-i)))
circuit.append(cirq.measure(*q,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Implements QFT on 3 qubits.

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Cirq Parameterized Gate

import cirq
import sympy

q = cirq.GridQubit(0,0)
theta = sympy.Symbol('theta')
circuit = cirq.Circuit(cirq.rx(theta)(q), cirq.measure(q,key='m'))
sim = cirq.Simulator()
result = sim.run(circuit,{theta:1.57},repetitions=500)
print(result)

Uses a parameterized rotation gate on a qubit.

Let’s Try →

Cirq Controlled Gates

import cirq

q0,q1 = cirq.GridQubit(0,0),cirq.GridQubit(0,1)
circuit = cirq.Circuit(cirq.H(q0), cirq.CZ(q0,q1), cirq.measure(q0,q1,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Demonstrates a controlled-Z gate between two qubits.

Let’s Try →

Cirq Swap Gate Example

import cirq

q0,q1 = cirq.GridQubit(0,0),cirq.GridQubit(0,1)
circuit = cirq.Circuit(cirq.SWAP(q0,q1), cirq.measure(q0,q1,key='result'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Swaps two qubits and measures them.

Let’s Try →

Cirq Measurement in Different Basis

import cirq

q = cirq.GridQubit(0,0)
circuit = cirq.Circuit(cirq.H(q), cirq.measure(q,key='X_basis'), cirq.measure(q,key='Z_basis'))
sim = cirq.Simulator()
result = sim.run(circuit,repetitions=500)
print(result)

Measures a qubit in X and Z bases.

Let’s Try →

Frequently Asked Questions about Cirq

What is Cirq?

Cirq is an open-source Python framework for quantum computing, developed by Google, focused on designing, simulating, and running quantum circuits on NISQ (Noisy Intermediate-Scale Quantum) devices.

What are the primary use cases for Cirq?

What are the strengths of Cirq?

What are the limitations of Cirq?

How can I practice Cirq typing speed?

CodeSpeedTest offers 10+ real Cirq code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.