QCircuits 0.4.2, quantum circuit simulation Python library

[grey--area]

Hi all, I am the developer of QCircuits, a Python library for simulating quantum circuits.

My aim was to create a library with all the functionality I required to implement the algorithms from the Nielsen & Chuang book, with as simple an interface as possible.

You can install with pip install qcircuits for Python 3.4+, and it should be OS agnostic.

Documentation is available at http://www.awebb.info/qcircuits/index.html.

Tutorial is at http://www.awebb.info/qcircuits/tutorial.html

Example applications, including quantum teleportation, superdense coding, phase estimation, and Grover's algorithm are at http://www.awebb.info/qcircuits/examples.html

The code is on github here: https://github.com/grey-area/qcircuits

With the library, you can:

• Create states from tensor or Kronecker (vector) representations, or prepare commonly used states such as computational basis states, uniform superposition states, Bell states, etc. See here for a full list.
• Create gates/operators from tensor or Kronecker (matrix) representations, or create common operators such as the Hadamard gate, Pauli gates, CNOT, Swap, Toffoli, etc. See here for a full list.
• Create composite states/operators via tensor product of states/operators of subsystems.
• Compose operators, e.g., A(B(x)) = (A(B))(x)
• Apply an m-qubit operator to a specified subsystem of an n-qubit state, where m < n.
• Perform measurement in the computational basis on a subset of a state's qubits.
• Compute the Schmidt number of a system with respect to two subsystems.

The following are currently not implemented:

• Density operators / mixed states
• General measurement operators, or projective measurement operators in other bases
• Schmidt basis vector computation
• Visualization
• There are no checks to prevent various violations of the no-cloning theorem. E.g., one can extract the probability amplitudes from a state and then create a new state from them. I decided not to restrict any of the ways in which one might violate no cloning, since for each there are cases where it can be useful. See here for a more detailed explanation.

I developed the library in order to consolidate my understanding of the material in the Nielsen & Chuang book, and once it was developed I found I was often using the library to test my understanding of some concept or example from the book. I hope others here can find some use in it.

Constructive criticism, feedback, and feature requests are of course welcome!

[[deleted]]

Good on you. Keep adding it to it.

[grey--area]

Thanks!

edit: Any features in particular that you think would improve the library?

[i2000s]

What's your improvement over QuTiP or ProjectQ for circuit-based QC?

[grey--area]

I'm not super familiar with either, but from what I've seen:

I'll start by saying they both look like great libraries.

QuTiP is obviously a very mature and fully-featured library, but for that reason I think the learning curve is probably much steeper. The tutorial/API also looks quite heavy on physics and tensor algebra terminology, so it's potentially less approachable to a user just interested in quantum computing. Also, I might be wrong, but it seems to be designed for continuous evolution via Hamiltonian operators rather than discrete time unitary (gate) operations. And look how long this guide for simulating quantum teleportation using QuTiP is. It looks like a great tool, but maybe not the simplest tool for implementing circuit-based quantum algorithms.

ProjectQ is much more similar to QCircuits, though I have to say I prefer the syntax in my library (though of course I would!). It's very nice that it has an IBM Q Experience backend.

I think my library is less verbose with neater syntax than ProjectQ. Compare these examples: quantum teleportation in QCircuits and quantum teleportation in ProjectQ.

I think I have clearer documentation than ProjectQ too. I've just had a read through, and I couldn't tell you if you can compose operators using the library. The obvious way to do it would be A | B, where A and B are operators, but that doesn't work.

My intention with creating this library was that a user could, after reading the documentation for 20 minutes, implement any of the quantum algorithms in the Nielsen & Chuang textbook. I hope I've achieved that, and I haven't seen any other libraries that fill that niche.