I am a beginner in quantum computing and I was meddling with HHL algorithm for my class project. Turns out the linear solver algorithms (mainly HHL algorithm) are removed from qiskit library (see https://qiskit.org/documentation/release_notes.html) and now exist only as a tutorial.

I want to ask what is the reason of deprecation? Is it only useful for understanding quantum algorithms and has no applicability? I am asking this to understand why it is not supported before going on with the improvements done with it.


2 Answers 2


If you look at section 4. Qiskit Implementation in the tutorial you will find a repository link where this repository now contains the HHL code that was formerly in Qiskit. You will see, if you read a bit further, the tutorial gives instruction for its installation as well.

Qiskit Terra 0.24 released yesterday (4th May 2023) and there is now an Algorithms Migration Guide published that outlines the rationale for the removal of both HHL and Shor.

Algorithms that were deprecated and are now removed entirely from qiskit.algorithms. These are algorithms that do not currently serve as building blocks for applications. Their main value is educational, and as such, will be kept as tutorials in the qiskit textbook. You can consult the tutorials in the following links:

    Linear Solvers (HHL) ,
    Factorizers (Shor)

Beyond what is mentioned in the main answer here, the Qiskit HHl implementation had a variety of issues that would need to be solved to go beyond the original use


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