Running the Bernstein-Vazirani algorithm on a real quantum computer

So far, we have always expected quantum computers to work perfectly. However, reality looks different and quantum computers results are still subject to errors. This section will explore how results look like when run on a real quantum computer, reasons behind it, and what actions can be taken to overcome this in the future.

In order to get a feeling for the current status of quantum computing hardware, let's take the algorithm we saw earlier and run it on today's quantum computer hardware.

This example uses the Bernstein-Vazirani algorithm that efficiently determines a secret code using just one call of a given black box (i.e. it solves the quantum combination lock). Instead of setting the last qubit to $|1\rangle$ from the start, we apply an X gate here instead. Check this section for more details.

The result of current quantum computers are subject to noise. Noise describes unwanted external disturbances that can cause errors in quantum computations and thus reduce the accuracy of the results. It's as if someone is making a lot of noise while you're trying to concentrate on a task 🙇‍♀️. It makes it harder to perform the task correctly.

When running the same quantum algorithm on an ideal quantum computer and a noisy quantum computer, the results obtained from the noisy one may be less accurate and less reliable than those from the ideal one. In fact, overcoming the problem of noise is one of the biggest challenges in building and using quantum computers, and researchers are actively working on improving quantum computing hardware and developing techniques to mitigate the effects of noise, thus advancing the overall reliability of quantum computers.