Qubits in the Classroom

In movies, quantum science is usually associated with chalkboards covered in equations. To some extent, this kind of abstraction is unavoidable: Quantum phenomena often involve behavior at scales that cannot be seen directly, and that do not match everyday intuition.

Thorlabs, a world-leading provider of optical equipment, donated tools that allow students to experiment with the quantum properties of light. (Credit: Bella Ciervo)

But, at least for Penn Engineering undergraduates, that’s now changing, thanks to a new suite of quantum teaching tools, including research-grade equipment donated by Thorlabs, a world-leading manufacturer of optical and scientific devices based in New Jersey.

“Hands-on experience fundamentally changes how students internalize quantum concepts,” says Lee Bassett, Associate Professor in Electrical and Systems Engineering (ESE) and Director of the Penn Center for Quantum Information, Engineering, Science and Technology (QUIEST). “It’s quite uncommon, if not unprecedented, for undergraduates to have access to this type of equipment in a course dedicated to experimental quantum science.”

In a recent conversation, Bassett and Anthony Sigillito, Assistant Professor in ESE, who was recognized this year by students for excellence as a research mentor, described how the new equipment is helping Penn Engineering make quantum science more engaging and accessible.

Can you describe the new equipment? What are students working with?

Lee Bassett (LB): First, it’s probably useful to clarify that we’re talking about two separate branches of quantum science: optical experiments, which involve manipulating light, and so-called “solid-state” experiments, which involve manipulating matter. Since quantum mechanics is ultimately about the smallest “quantity” of something that can be measured, understanding these principles in the context of both light and matter is essential.

Anthony Sigillito (AS): To study the quantum properties of light, we now have specialized tables equipped with lasers, mirrors, lenses and other components. These allow students to generate a single photon — the smallest unit of light — and study how it behaves.

Students with no prior experience in quantum physics can now conduct hands-on experiments that demonstrate fundamental quantum properties, like the ability of light to be in two places at once. Here, a student works with teaching assistant Joseph Minella, at right. (Credit: Bella Ciervo)

LB: You might expect that a photon hitting a mirror would go left or right, like a person choosing how to take a fork in the road. But quantum mechanics tells us that the photon can actually travel both paths. This is extremely counterintuitive, and the mathematics needed to describe it is abstract, involving linear algebra and complex numbers.

AS: Using the new experimental apparatus, students can generate a single photon, split it using a particular type of mirror and then detect it using specialized research-grade hardware. In this way, they can collect data showing that the photon behaves as though it has traveled both paths and interfered with itself.

LB: It’s one thing to be told in a lecture that a photon can effectively be in two places at once, or to derive the result mathematically, but another entirely to see the two paths with your own eyes and collect data yourself that proves it.

How does the other equipment work?

Some of the equipment that students use to create and test a qubit, the fundamental building block of a quantum computer. (Credit: Bella Ciervo)

AS: Students have probably heard of quantum computers, which hold tremendous promise for greater security, energy efficiency and computational power. We now have the equipment for students to essentially assemble and control the basic building block of a quantum computer — a qubit — themselves, one step at a time.

LB: In a regular computer, information is built from bits, which are typically represented as 0s and 1s — this is where you get words like megabyte, or MB, which is a certain number of bits, and represents a given amount of data.

What makes qubits unique is that they are not limited to being simply 0 or 1 in the same way. They can exist in combinations of those states, which is part of what gives quantum computing its unusual potential. But why qubits work this way is hard to understand in the abstract.

Assistant Professor Anthony Sigillito, at left, holds the interior compartment of a TeachSpin module, which contains water whose proton spins students manipulate using custom hardware they develop over the course of a semester. (Credit: Bella Ciervo)

AS: Qubits rely on quantum properties such as spin, which is carried by subatomic particles like electrons or protons. You can think of the spin like a tiny bar magnet, just a billionth of a meter across. The direction the magnet points is like the “0” or “1” in a classical computer.

Our lab now has modules — which Penn Engineering purchased from TeachSpin, a maker of scientific teaching equipment — to generate the magnetic fields necessary to manipulate the spins.

LB: In essence, students use the magnetic field to change the direction of the spins of protons in water molecules, which are contained in a small, plastic cylinder inside the module. Of course, all of this is much too small to perceive using any kind of standard lab equipment, like a microscope, so we also have specialized equipment for detecting the proton spins.

Students test their qubit. The copper cylinder in the foreground contains a cylinder of water whose proton spins the students are manipulating and monitoring. (Credit: Bella Ciervo)

AS: As part of the course, students actually build the equipment that both controls and detects the spins, and thus the qubits, step by step, over the course of several weeks. They start with the apparatus provided by TeachSpin, and gradually replace it part-by-part with custom hardware running software that our team has developed, combining a device called a Moku:Go and an Arduino microcontroller. This enables experiments that go far beyond what the TeachSpin equipment can do out of the box.

What do students ultimately learn by performing experiments like these?

LB: Even with just one qubit, students are ultimately able to run simple quantum circuits, test whether those circuits produce the expected results and benchmark how accurately their qubit performs, giving them firsthand insight not just into how difficult it is to assemble and maintain quantum computers, but also how much potential these devices hold.

The goal is for students to understand exactly what quantum properties they’re looking for and how measuring those properties works, using the same equipment you would find in a professional research lab.

AS: Students certainly learn quantum concepts, but they also learn something broader: how to think like experimental engineers. Quantum systems are very sensitive, so students have to understand what they are measuring, what their instruments can and cannot detect, where noise or error might enter the system and how to tell whether the result is real.

Students adjusting and testing the components of their qubit, a process that teaches critical engineering skills, with teaching assistant Jeiko Pujols, at right. (Credit: Bella Ciervo)

That matters well beyond quantum science. Whether an engineer is working on quantum computers, medical devices, space systems or clean water technologies, they need to know how to define a goal, design a test, interpret data and troubleshoot when reality does not match the ideal version in a textbook. This lab gives students a heightened environment for practicing those skills.

LB: And because students are doing the experiments themselves, the concepts become much more tangible. Instead of simply being told that photons can behave in counterintuitive ways, or that qubits can be controlled and measured, students can see those ideas emerge from experiments they helped assemble. That makes quantum science feel less remote and more like something they can participate in.

Students interested in learning more about the new quantum lab equipment can register for ESE 3200 The Qubit Lab: A Hands-on Introduction to Quantum Devices, or reach out to Anthony Sigillito, Assistant Professor in ESE, at asigilli@seas.upenn.edu.