This past summer, I worked on the Quantum Systems Team at Microsoft. Every December the group puts together a Q# Advent Calendar filled with great blog posts. I thought I’d share my work on the Quantum Systems Team, as well as my general experience being a Microsoft Intern.

## Quantum Resource Estimation

### Motivation

Resource estimation is an important concept in quantum programs. As the name implies, resource estimation allows a quantum researcher to understand the simulated resources required to run a particular algorithm, usually measured in logical qubits. But resource estimation can provide much more than that. We can track the number and types of gates required to run a program. And, by continuously evaluating a quantum program against a common set of metrics, we can understand the improvement of our theoretical approaches.

### Toy Example

To be more concrete, we can look at the outputs of the QDK Resource Estimation tool on various Q# implementations of quantum programs that implement the following function, where $n=3$. (known as the majority of three ) This example is taken from a great presentation given by the QDK Team at IEEE Quantum Week 2020.

$\begin{split} \langle p_1,\dots, p_n \rangle &= \rm Majority (p_1, \dots, p_n) \\ \\ &= \left \lfloor \frac{1}{2} + \frac{((\sum^n_{i=1} p_i) - 1/2}{n} \right \rfloor \end{split}$

namespace Majority {
open Microsoft.Quantum.Canon;
open Microsoft.Quantum.Convert;
open Microsoft.Quantum.Intrinsic;
open Microsoft.Quantum.Synthesis;

operation ApplyMajorityUsingInts(x1 : Qubit, x2: Qubit, x3 : Qubit,
y : Qubit) : Unit is Adj + Ctl {
...
}

operation ApplyMajorityUsingCCNOTs(x1 : Qubit, x2: Qubit, x3 : Qubit,
y : Qubit) : Unit is Adj + Ctl {
...
}

operation ApplyMajorityUsingTruthTable(x1 : Qubit, x2: Qubit, x3 : Qubit,
y : Qubit) : Unit is Adj + Ctl {
...
}

operation ApplyMajorityUsingCNOTTransformation(x1 : Qubit, x2: Qubit,
x3 : Qubit, y : Qubit) : Unit is Adj + Ctl {
...
}

}


We won’t dive into the implementation details of each of these functions since that is not the focus of this blog post. (and, they were already covered in the talk linked above ) What is important, though, is that they do produce significantly different qubit usage counts and gate counts as noted in the table below.

Implementation CNOT Clifford T T Depth Qubits
Ints 120 30 84 56 5
CCNOTs 30 6 21 15 4
Truth Table 14 3 8 6 4
CCNOT Transformation 15 2 7 5 4

Now imagine you are a researcher trying to iteratively improve upon your algorithm’s performance. Often times, performance in one of these metrics comes at the cost of another area. (known as a Pareto front ) And after speaking with quantum researchers, I noted that they all mention the tedium and sometimes error filled process of tracking experiment results.

### Approach

Enter the resource estimation dashboard, an all-in-one tool to both measure and track the performance of different quantum programs. The idea here is to track experiment results using a consistent format and upload the results to a central platform. As you iteratively improve on your algorithm–or run your algorithm with a different set of parameters, you will see plots that result in points along a Pareto curve.

The screenshot below is taken from the MVP that I built over the summer. It digitizes the main plots showing the tradeoffs suggested in the work to reduce the T-Depth of quantum circuits. One could imagine a website with this page, along with others pages, for specific quantum applications covered in the Quantum Algorithm Zoo. In fact, you get a two for one, since both the results and code are collated together, you get reproducibility of results for free. (that is, if the project was run using a public CI service like GitHub Actions)

In fact, this concept is not all that new and has been put to great effect in the ML community and a number of startups and projects are working on problems in that space. Papers with Code, most notably, has become the go-to source for ML researchers to get a rough sense of the progression of the state of the art in any particular problem area. The work I implemented over the summer put together an MVP for a hosted runner that executed Q# programs against the open source QDK Resource Estimator. For those curious, the stack was a Next.js frontend with a .NET API backend server. The above is just a sample of the overall project vision, and I hope gives you an idea of the types of exciting work the Quantum Systems team is working on.

## The Microsoft Intern Experience

Besides my core work on the Quantum Systems Team, I also enjoyed my time as a Microsoft Intern! Although there were a number of fantastic intern events, two in particular, stand out in my memory: the Microsoft Intern Game and serving as a moderator for a “pool-side” chat with a Microsoft Researcher.

For the intern game, we paired up into groups and competed in an “Amazing Race” style virtual event with a Casino Heist theme. The Microsoft team behind the event had developed a custom virtual platform with mini-games that had real world puzzles that were mailed out to us along with actors, to boot. It was a great time. For my moderation panel, I got a chance to chat with Kevin Yang a senior researcher working on bioinformatics in Microsoft’s Cambridge office. We chatted about his past as a PhD student and his current work at Microsoft along with why he’s excited about protein engineering. Besides the events, the intern team was very kind to send the interns a lot of swag–some of which I wear all the time like my quantum team sweatshirt.

Overall, I cannot speak more highly about my experience as an intern on the Quantum Team and– I hear they are looking for more interns, so I would definitely recommend you check them out.