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Different types of target profiles in Azure Quantum

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Quantum devices are still an emerging technology and unfortunately not all of them can run every Q# code. As such, you need to keep some restrictions in mind when developing quantum programs. The target profile types are used to define the capabilities of the quantum devices that you can target with your Q# programs, that is, the capabilities of the current quantum devices available in Azure Quantum.

This article discusses the different types of target profiles in Azure Quantum, their limitations, and how to configure them using the Quantum Development Kit (QDK).

Target profiles and their limitations

Currently, Azure Quantum and the QDK manage three different target profiles, depending on their ability to run quantum intermediate representation (QIR) programs.

  • Unrestricted: This profile can run any QIR program, and thus any Q# program, within the limits of memory for simulators or the number of qubits for physical quantum computers.
  • QIR base: 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.
  • QIR Adaptive RI: 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 compare values of type Result as part of conditions within if statements in operations, allowing mid-circuit measurement.

Create and run programs for Unrestricted target profile

Unrestricted target profiles can run any program, meaning you can write Q# programs without functionality restrictions. Azure Quantum doesn't provide any target with this profile. However, you can run Unrestricted Q# programs on simulators provided by the QDK.

Configure Unrestricted target profile

In Visual Studio Code:

  1. Select View -> Command Palette and type Q#: Set the Azure Quantum QIR target profile. Press Enter.
  2. Select Unrestricted.

In Python, you can set the target profile using the qsharp.init method.

qsharp.init(target_profile=qsharp.TargetProfile.Unrestricted)

Create and run programs for QIR Base target profile

QIR Base target profiles 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 don't support equality comparison.

For example, this operation can't be run on a QIR Base target:

    operation FlipQubitOnZero() : Unit {
        use q = Qubit();
        if M(q) == Zero {
            X(q);
        }
    }

If you try to run this operation on a QIR Base target, the operation will fail because it does a comparison using a measurement result (M(q) == Zero) to control the computation flow with an if statement. The same is applicable to any type of conditional branching, such as elif and else statements.

Configure QIR Base target profile

In Visual Studio Code:

  1. Select View -> Command Palette and type Q#: Set the Azure Quantum QIR target profile. Press Enter.
  2. Select QIR base.

In Python, you can set the target profile using the qsharp.init method.

qsharp.init(target_profile=qsharp.TargetProfile.Base)

Supported targets for QIR Base target profile

Currently, the following QIR Base targets are available in Azure Quantum:

Create and run programs for QIR Adaptive RI target profile

QIR Adaptive RI profile targets can run a wide variety of Q# applications, with some constraints. This profile type supposes an improvement over QIR Base profiles, but still is subject to some limitations.

QIR Adaptive RI profile targets allow measurement-based conditional operations and mid-circuit measurements, meaning that qubits can be selectively measured at a point other than the final statement of a quantum program, and the output of the measurement can be used in other operations. Mid-circuit measurement enables multiple measurements at any point throughout the quantum program. The quantum information of the measured qubits collapses to a classical state (zero or one), but the non-measured qubits remain in their quantum state.

In Q# when measuring a qubit, a value of type Result is returned. If you want to use this result in a conditional statement, you have to directly compare in the conditional statement. The corresponding conditional blocks may not contain return or set statements.

For example, the following Q# code would be allowed in a QIR Adaptive RI target:

operation MeasureQubit(q : Qubit) : Result { 
    return M(q); 
}

operation SetToZero(q : Qubit) : Unit {
     if MeasureQubit(q) == One { X(q); }
}

Configure QIR Adaptive RI target profile

In Visual Studio Code:

  1. Select View -> Command Palette and type Q#: Set the Azure Quantum QIR target profile. Press Enter.
  2. Select QIR Adaptive RI.

In Python, you can set the target profile using the qsharp.init method.

qsharp.init(target_profile=qsharp.TargetProfile.Adaptive_RI)

Supported targets for QIR Adaptive RI target profile

Currently, the following QIR Adaptive RI targets are available in Azure Quantum: