Could Super Conducting Graphene Quantum Dots Lead to Solid-State Qubits?

Quantum dots of graphene help isolate the elusive phenomenon of Andreev bound states

2 min read
Could Super Conducting Graphene Quantum Dots Lead to Solid-State Qubits?

Quantum computers are sometimes referred to as the Holy Grail of computing, or maybe the Philosopher’s Stone of computing might be another appropriate medieval reference to a nearly unattainable quest. In any case, while some outfits have claimed they have achieved fairly significant quantum computer prototypes despite being met with skepticism, creating a quantum computer that can calculate something beyond what a kid in elementary school can factor has proven difficult.

One of the fundamental issues researchers have faced in developing quantum computers has been the problem of getting the computers to maintain more than a few quantum bits (or qubits). One of the more promising ways of getting beyond a mere seven qubits has been the use of quantum dots.

Now researchers at the University of Illinois led by Nadya Mason have brought a new wrinkle into this field of research. The research, which was initially published in the journal Nature Physics, was looking at what happens when a normal conducting material like a metal or graphene is sandwiched between two superconducting materials and observing the interface of the materials.

While it has been observed previously that normal metals in these instances take on the characteristics of the superconductor material when current is passed through it (namely, that it too will pass electron pairs through it rather than a single stream of electrons), the Illinois researchers by working with graphene quantum dots were able to better understand the fundamental physics at play: Andreev bound states (ABS).

To date, ABS have proven to difficult to both measure and observe. At is at this point that the researchers developed a novel method to isolate individual ABS by connecting probes to quantum dots made from graphene. As quantum dots do they confined the confined ABS into discrete energy states, which permitted the researchers to not only measure the ABS but to manipulate them.

"Before this, it wasn't really possible to understand the fundamentals of what is transporting the current," Mason said. "Watching an individual bound state allows you to change one parameter and see how one mode changes. You can really get at a systematic understanding. It also allows you to manipulate ABS to use them for different things that just couldn't be done before."

The concurrence of the two nanomaterials, graphene and quantum dots, along with the superconducting material made the breakthrough possible. 

"This is a unique case where we found something that we couldn't have discovered without using all of these different elements – without the graphene, or the superconductor, or the quantum dot, it wouldn't have worked. All of these are really necessary to see this unusual state," Mason said.

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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