Jainendra Jain, physicist at Penn State, weighs in on the newly announced quantum computer chip and how theoretical, basic research fuels innovation

More than 30 years ago, Penn State physicist Jainendra Jain pioneered the theory of a new state of matter called the fractional quantum Hall effect, whose discoverers were awarded the Nobel Prize in Physics in 1998. Jain described it as a liquid of certain strange particles that he called composite fermions.

Under certain conditions, composite fermions form a superconductor — or a material that can conduct electricity without losing any energy at low temperatures — that theorists predicted would contain an even stranger particle, called a Majorana, which is its own antiparticle — a particle with the same mass but different charge.

Theorists envisioned that the Majorana particles, which mirror themselves as their own antiparticles, could be used to perform fault-tolerant quantum computation. This ability to run calculations while simultaneously correcting errors is essential for advancing quantum computing for real-world, industrial scale applications.

Last week (Feb. 19), Microsoft announced a potential breakthrough in quantum computing based on these long-theorized but experimentally unconfirmed Majorana particles. They also published a paper in the journal Nature on some of the work described in their announcement.

In the following Q&A, Jain, an Evan Pugh University Professor and Erwin W. Müller Professor in Physics, spoke about his work on the theory of composite fermions, how it relates to Microsoft’s announcement and why skepticism is a valuable element of scientific discovery.

Q: How does theoretical physics support real-world design?

Jain: Quantum physics is the science of how tiny particles — like photons, particles of light, and electrons — behave in ways that seem counter to our everyday experience. Unlike objects we encounter in our daily lives, these tiny particles can pass through barriers and can seemingly exist in multiple places at once, until they are observed.

It turns out that physicists can create new particles in the laboratory, which are unlike any particles nature has given us. And, sometimes, they have incredibly strange properties and do things which the old, familiar particles couldn’t. Such particles are called emergent particles. If we can understand them, then maybe we can use them to develop new materials and technologies for the benefit of humanity.

I am on the theoretical understanding side of this spectrum, but I work closely with scientists who test whether the theories correspond to reality. The news from Microsoft is an example of how basic research at universities could lead to real-world applications that drive innovation — like quantum computers.

Q: What is a quantum computer and how would the Majorana particle help?

Jain: A normal computer works with “bits,” which are binary digits and comprise the smallest data unit. It can code either one or zero, on or off, and many of them together in a certain order convey larger messages. A quantum bit, or qubit, offers additional possibilities: it can be on, off or in any superpositions of the two, including on and off at the same time — just like the famous thought experiment “Schrodinger’s cat” in which a cat in a box is both alive and dead at the same time, until someone opens the box to check, at which time a definitive state of dead or alive is achieved.

When you link many qubits together, the possibilities grow exponentially. This allows a quantum computer to do certain types of calculations, at least theoretically, much faster than a classical computer. One can come up with examples where all the world’s current computers operating together for decades would not be able to perform the calculations of one quantum computer in a day.

One of the biggest hurdles in quantum computing is that information degrades because of interaction with noise, or interference from the environment or elsewhere in the system. This can lead qubits to collapse into a definite state, introducing errors. This is where the rather strange Majorana particles come in.

Two Majorana particles can produce either nothing or a whole fermion, which make the on and off states of a single qubit. Unlike many other qubits, the information here can be stored non-locally in a topological fashion — meaning the two Majorana particles forming a qubit could be far apart. Then, since neither Majorana contains the full information, any local noise cannot switch off to on or on to off. This enables the qubits to hold information without information loss.

Q: Tell me more about your work. What are composite fermions and how do they relate to applications like quantum computing?

Jain: My work had a role in the unlikely sequence of events that led to the idea of Majorana-based quantum computation. I think this is an example of how ideas evolve and mutate and move into unexpected directions.