Shrinking Superconducting Qubits for Quantum Computing With Atom-Thin Materials

Utilizing 2D supplies, researchers have constructed superconducting qubits which might be a fraction of the scale of earlier qubits, paving the best way for smaller quantum computer systems.

For quantum computer systems to surpass their classical counterparts in velocity and capability, their qubits—that are superconducting circuits that may exist in an infinite mixture of binary states—must be on the identical wavelength. Attaining this, nevertheless, has come at the price of measurement. Whereas the transistors utilized in classical computer systems have been shrunk all the way down to nanometer scales, superconducting qubits lately are nonetheless measured in millimeters—one millimeter is one million nanometers.Mix qubits collectively into bigger and bigger circuit chips, and you find yourself with, comparatively talking, a giant bodily footprint, which suggests quantum computer systems take up lots of bodily house. These usually are not but gadgets we will carry in our backpacks or put on on our wrists.

To shrink qubits down whereas sustaining their efficiency, the sphere wants a brand new technique to construct the capacitors that retailer the vitality that “powers” the qubits. In collaboration with Raytheon BBN Applied sciences, Wang Fong-Jen Professor James Hone’s lab at Columbia Engineering not too long ago demonstrated a superconducting qubit capacitor constructed with 2D supplies, rendering it a fraction of the scale of earlier capacitors.

To construct qubit chips beforehand, engineers have had to make use of planar capacitors, which set the mandatory charged plates aspect by aspect. Stacking these plates would save house, however the metals utilized in standard parallel capacitors intervene with qubit data storage. Within the present work, printed on November 18 in NanoLetters, Hone’s PhD college students Abhinandan Antony and Anjaly Rajendra sandwiched an insulating layer of boron nitride between two charged plates of superconducting niobium diselenide. These layers are every only a single atom thick and held collectively by van der Waals forces, the weak interplay between electrons. The group then mixed their capacitors with aluminum circuits to create a chip containing two qubits with an space of 109 sq. micrometers and simply 35 nanometers thick—that’s 1,000 instances smaller than chips produced below standard approaches.

After they cooled their qubit chip down to simply above absolute zero, the qubits discovered the identical wavelength. The group additionally noticed key traits that confirmed that the 2 qubits had been turning into entangled and performing as a single unit, a phenomenon generally known as quantum coherence; that will imply the qubit’s quantum state could possibly be manipulated and skim out through electrical pulses, mentioned Hone. The coherence time was brief—a bit over one microsecond, in comparison with about 10 microseconds for a conventionally constructed coplanar capacitor, however that is solely a primary step in exploring the usage of 2D supplies on this space, he mentioned.

Optical micrograph of the group’s superconducting qubit chip that’s 1,000 instances smaller than others made with standard fabrication strategies. Credit score: Abhinandan Antony et al./Columbia Engineering

Separate work printed on arXiv final August from researchers at MIT additionally took benefit of niobium diselenide and boron nitride to construct parallel-plate capacitors for qubits. The gadgets studied by the MIT group confirmed even longer coherence instances—as much as 25 microseconds—indicating that there's nonetheless room to additional enhance efficiency.From right here, Hone and his group will proceed refining their fabrication strategies and check different varieties of 2D supplies to extend coherence instances, which mirror how lengthy the qubit is storing data. New machine designs ought to have the ability to shrink issues down even additional, mentioned Hone, by combining the weather right into a single van der Waals stack or by deploying 2D supplies for different elements of the circuit.

“We now know that 2D supplies might maintain the important thing to creating quantum computer systems potential,” Hone mentioned. “It's nonetheless very early days, however findings like these will spur researchers worldwide to think about novel purposes of 2D supplies. We hope to see much more work on this course going ahead.”

Reference: “Miniaturizing Transmon Qubits Utilizing van der Waals Supplies” 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.
DOI: 10.1021/acs.nanolett.1c04160