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Target profile types in Azure Quantum

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This article discusses the different type of target profile types available in the quantum computing providers in Azure Quantum. At this time, because of the early development stage of the field, quantum devices have some limitations and requirements for programs that run on them.

Quantum Processing Units (QPU): different profiles

A Quantum Processing Unit (QPU) is a physical or simulated processor that contains a number of interconnected qubits that can be manipulated to compute quantum algorithms. It's the central component of a quantum computer or quantum simulator.

Quantum devices are still an emerging technology, and not all of them can run all Q# code. As such, you need to keep some restrictions in mind when developing programs for different targets. Currently, Azure Quantum and the QDK manage three different profiles for QPUs:

  • Full: This profile can run any Q# program within the limits of memory for simulators or the number of qubits for physical quantum computers.
  • No Control Flow: This profile can run any Q# program that doesn't require the use of the results from qubit measurements to control the program flow. Within a Q# program targeted for this kind of QPU, values of type Result don't support equality comparison.
  • Basic Measurement Feedback: This profile has limited ability to use the results from qubit measurements to control the program flow. Within a Q# program targeted for this kind of QPU, you can only compare values of type Result as part of conditions within if statements in operations. The corresponding conditional blocks might not contain return or set statements.

Create and run applications for Full profile targets

Full profile targets can run any Q# program, meaning you can write programs without functionality restrictions. Azure Quantum does not provide any target with this profile yet, but you can try any Q# program locally using the full state simulator or the resources estimator from the QDK.

If you need help setting up your environment to run Q# programs locally, see Set up Azure Quantum.

You can also explore different Q# code samples to run locally with the QDK.

Create and run applications for No Control Flow profile targets

No Control Flow profile targets can run a wide variety of Q# applications, with the constraint that they can't use results from qubit measurements to control the program flow. More specifically, values of type Result do not support equality comparison.

For example, this operation can NOT be run on a No Control Flow target:

    operation SetQubitState(desired : Result, q : Qubit) : Result {
        if (desired != M(q)) {
            X(q);
        }
    }

Trying to run this operation on a No Control Flow target will fail because it evaluates a comparison between two results (desired != M(q)) to control the computation flow with an if statement.

Note

Currently, there is an additional limitation for this type of profile target: you can't apply operations on qubits that have been measured, even if you don't use the results to control the program flow. This limitation is not inherent to this profile type but is circumstantial to the situation of the Public Preview.

Presently, these No Control Flow targets are available for Azure Quantum:

Create and run applications for Basic Measurement Feedback targets

Basic Measurement Feedback profile targets can run a wide variety of Q# applications, with the constraint that you can only compare values of type Result as part of conditions within if statements in operations. The corresponding conditional blocks may not contain return or set statements. This profile type supposes an improvement over No Control Flow profiles, but still is subject to some limitations.

For example, the preceding SetQubitStateoperation can be used in a Basic Measurement Feedback target as long as you don't include any return or set statement within the if block. For example, the following operation can't be used in a Basic Measurement Feedback target:

    operation SetQubitState(desired : Result, q : Qubit) : Result {
    if desired != M(q) {
        X(q);
        return M(q);
    }
}

Presently, these Basic Measurement Feedback targets are available for Azure Quantum: