QASM

 Below, how-to use the QASM simulator. QASM is a machine-language implementation

of circuits, but one can interact with it using AER python.

                                                         

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A fun recipe for 'MilkBread' came through French-language Facebook this morning. It is bread 

pudding using a bit of condensed milk. 

                                                                                

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Gemini Pro:

Qiskit 1.2; does the QASM simulator report outcomes different from AERSimulator. Please explain.

In Qiskit 1.2, the QASM simulator and AER simulator are two distinct types of simulators with different purposes and capabilities. The QASM simulator is designed to simulate quantum circuits with noise and represents measurement outcomes through a sampling process [[3](https://qiskit.github.io/qiskit-aer/stubs/qiskit_aer.QasmSimulator.html)][[7](https://docs.quantum.ibm.com/api/qiskit/0.19/qiskit.providers.aer.QasmSimulator)]. It produces results by simulating the execution of a circuit in the presence of noise, which can result in a distribution of outcomes that reflect realistic noise effects in quantum computation [[5](https://qiskit.github.io/qiskit-aer/)][[6](https://github.com/Qiskit/qiskit-aer)].

On the other hand, the AER simulator encompasses a range of simulation methods, including noise-free simulations as well as those that include noise. It supports several simulation methods, such as statevector, density matrix, and stabilizer, and can return exact results of quantum circuits under these methods [[2](https://qiskit.github.io/qiskit-aer/tutorials/1_aersimulator.html)][[5](https://qiskit.github.io/qiskit-aer/)]. In noise-free mode, AER can provide precise statevector or density matrix representations of the quantum circuit, while noise-inclusive simulations can still reflect distributions caused by noise [[1](https://quantumcomputing.stackexchange.com/questions/24072/what-are-the-differences-between-qiskits-aersimulator-qasmsimulator-and-statev)][[2](https://qiskit.github.io/qiskit-aer/tutorials/1_aersimulator.html)].

Therefore, the key difference between the two is that while QASM is inherently focused on simulating noisy quantum circuits and therefore produces outcomes that account for noise-related randomness, AER offers broader functionality including both ideal and noisy simulations. This means that the outcomes reported by QASM, especially in a noisy context, may differ from a noise-free AER simulation but should align more closely when AER is configured to simulate noise [[5](https://qiskit.github.io/qiskit-aer/)][[7](https://docs.quantum.ibm.com/api/qiskit/0.19/qiskit.providers.aer.QasmSimulator)]. 

Running a circuit using the QASM simulator on a real quantum computer involves executing the circuit as specified in the Quantum Assembly (QASM) language, which describes the gates and operations on qubits. When you run a QASM circuit on a real quantum computer, the process goes beyond simulation: it involves actual physical qubits and hardware. Consequently, the outcomes of your quantum circuit may differ from those obtained in a simulator, primarily due to the presence of noise factors inherent in real quantum systems [[1](https://www.nature.com/articles/s41467-024-46402-9)][[5](https://www.technologyreview.com/2024/01/04/1084783/quantum-computing-noise-google-ibm-microsoft/)]. 

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What happens if I run a circuit with QASM on a real quantum computer?

Quantum computers are extremely sensitive to disturbances such as thermal fluctuations or electromagnetic interference, which can introduce errors into computations [[5](https://www.technologyreview.com/2024/01/04/1084783/quantum-computing-noise-google-ibm-microsoft/)]. Thus, the results from running a QASM circuit on a real device are generally influenced by decoherence, gate errors, and measurement errors, factors which may lead to results that are less accurate or precise compared to simulated outcomes on an idealized simulator [[5](https://www.technologyreview.com/2024/01/04/1084783/quantum-computing-noise-google-ibm-microsoft/)][[6](https://www.bcg.com/publications/2024/long-term-forecast-for-quantum-computing-still-looks-bright)].

In practical terms, this means that if you run a QASM circuit on a real quantum computer, you should expect to see some degree of deviation in the outcome distributions when compared to the QASM simulation results. It is important to apply error mitigation techniques and increase the number of repetitions (shots) to obtain a more reliable statistical representation of the results if running a real-world application [[3](https://www.quera.com/blog-posts/current-and-future-state-of-quantum-computing)][[6](https://www.bcg.com/publications/2024/long-term-forecast-for-quantum-computing-still-looks-bright)].