Shrinking qubits for quantum computing with atom-thin supplies

For quantum computer systems to surpass their classical counterparts in pace and capability, their qubits—that are superconducting circuits that may exist in an infinite mixture of binary states—have to be on the identical wavelength. Reaching this, nevertheless, has come at the price of dimension. Whereas the transistors utilized in classical computer systems have been shrunk all the way down to nanometer scales, superconducting qubits today are nonetheless measured in millimeters—one millimeter is a million nanometers.

Mix qubits collectively into bigger and bigger circuit chips, and you find yourself with, comparatively talking, an enormous bodily footprint, which implies quantum computer systems take up lots of bodily area. These are usually not but units we will carry in our backpacks or put on on our wrists.

To shrink qubits down whereas sustaining their efficiency, the sector wants a brand new strategy 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 just lately demonstrated a superconducting qubit capacitor constructed with 2D supplies that is a fraction of earlier sizes.

To construct qubit chips beforehand, engineers have had to make use of planar capacitors, which set the required charged plates facet by facet. Stacking these plates would save area, however the metals utilized in typical parallel capacitors intervene with qubit data storage. Within the present work, revealed on November 18 in Nano Letters, Hone’s Ph.D. college students Abhinandan Antony and Anjaly Rajendra sandwiched an insulating layer of boron nitride between two charged plates of superconducting niobium dieselenide. These layers are every only a single atom thick and held collectively by van der Waals forces, the weak interplay between electrons. The workforce 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 is 1,000 occasions smaller than chips produced below typical approaches.

Once they cooled their qubit chip down to simply above absolute zero, the qubits discovered the identical wavelength. The workforce additionally noticed key traits that confirmed that the 2 qubits had been turning into entangled and appearing as a single unit, a phenomenon referred to as quantum coherence; that may imply the qubit’s quantum state could possibly be manipulated and browse out by way of electrical pulses, mentioned Hone. The coherence time was quick—a bit over 1 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.

Separate work revealed on arXiv in August from researchers at MIT additionally took benefit of niobium diselenide and boron nitride to construct parallel-plate capacitors for qubits. The units studied by the MIT workforce confirmed even longer coherence occasions—as much as 25 microseconds—indicating that there’s nonetheless room to additional enhance efficiency.
From right here, Hone and his workforce will proceed refining their fabrication methods and check different kinds of 2D supplies to extend coherence occasions, which replicate how lengthy the qubit is storing data. New system 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 could maintain the important thing to creating quantum computer systems attainable,” Hone mentioned. “It’s nonetheless very early days, however findings like these will spur researchers worldwide to think about novel functions of 2D supplies. We hope to see much more work on this route going ahead.”