Using 2D materials, researchers have built superconducting qubits that are a fraction of the size of previous qubits, paving the way for smaller quantum computers.
To shrink qubits down while maintaining their performance, the field needs a new way to build the capacitors that store the energy that “powers” the qubits. In collaboration with Raytheon BBN Technologies, Wang Fong-Jen Professor James Hone’s lab at Columbia Engineering recently demonstrated a superconducting qubit capacitor built with 2D materials, rendering it a fraction of the size of previous capacitors.
To build qubit chips previously, engineers have had to use planar capacitors, which set the necessary charged plates side by side. Stacking those plates would save space, but the metals used in conventional parallel capacitors interfere with qubit information storage. In the current work, published on November 18 in NanoLetters, Hone’s PhD students Abhinandan Antony and Anjaly Rajendra sandwiched an insulating layer of boron nitride between two charged plates of superconducting niobium diselenide. These layers are each just a single atom thick and held together by van der Waals forces, the weak interaction between electrons. The team then combined their capacitors with aluminum circuits to create a chip containing two qubits with an area of 109 square micrometers and just 35 nanometers thick—that’s 1,000 times smaller than chips produced under conventional approaches.
When they cooled their qubit chip down to just above absolute zero, the qubits found the same wavelength. The team also observed key characteristics that showed that the two qubits were becoming entangled and acting as a single unit, a phenomenon known as quantum coherence; that would mean the qubit’s quantum state could be manipulated and read out via electrical pulses, said Hone. The coherence time was short—a little over one microsecond, compared to about 10 microseconds for a conventionally built coplanar capacitor, but this is only a first step in exploring the use of 2D materials in this area, he said.
“We now know that 2D materials may hold the key to making quantum computers possible,” Hone said. “It is still very early days, but findings like these will spur researchers worldwide to consider novel applications of 2D materials. We hope to see a lot more work in this direction going forward.”
Reference: “Miniaturizing Transmon Qubits Using van der Waals Materials” by Abhinandan Antony, Martin V. Gustafsson, Guilhem J. Ribeill, Matthew Ware, Anjaly Rajendran, Luke C. G. Govia, Thomas A. Ohki, Takashi Taniguchi, Kenji Watanabe, James Hone and Kin Chung Fong, 18 November 2021, NanoLetters.