This post summarizes things I've learned over the 7th week of my Quantum Computing Ultralearning challenge, and should be considered as study notes instead of a fully-explained-and-very-detailed article on quantum gates, since other experts have done that work (see references).
Programming #
Code: https://colab.research.google.com/drive/1t_fjICucjdmBqfQIa4LQNiy8um7dyg6e?usp=sharing .
Most of the things I learned this week are about Cirq, which can be summarized in below points:
Moments #
A Cirq circuit (qubit grid) is a collection of moments.
Each moment is a "column" in the qubit grid, which contains operations that running at the same time.
Image source: [1].
Devices #
- Using real quantum devices? --> there are hardware
constraints on the circuit, such as only allowing operations on adjacent qubits. - How to capture these requirements / constraints? --> creating a circuit with a Device.
- What does a Device do? --> validating the operations you add to the circuit to make sure that no illegal operations are added.
Simulation #
Cirq supports two types of simulation: pure state and mixed state.
I don't have much experience with the mixed state simulation at this moment, but it seems that the mixed state can simulate a larger class of noisy circuits than the pure state.
There are also noticable features of the Cirq simulation:
- Stepping: allows viewing qubit states at each step (moment), without changing their actual states (by measurement).
- Parameterized values: gates can have
Symbol values, which can be resolved at run-time.
References #
1. https://quantumai.google/cirq/circuits
2. https://quantumai.google/cirq/tutorials/basics#circuits_and_moments
3. https://quantumai.google/cirq/simulation
4. https://quantumai.google/cirq/tutorials/basics#simulation
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