Qubits, which are superconducting circuits that can exist in an endless number of binary states, must be on the same wavelength for quantum computers to outperform their classical counterparts in terms of speed and capacity. Quantum computing is a new technology that uses quantum physics to address issues that are too difficult for traditional computers to solve.
However, achieving this has come at the expense of size. Unlike traditional computer transistors, which have been miniaturized to nanoscale scales, superconducting qubits are still measured in millimeters. One million nanometers equals one millimeter.
Quantum computer programming does not necessitate considerable retraining or the use of new coding languages. Nonetheless, it will provide you with access to a completely new computing paradigm.
When you combine qubits into larger and larger circuit chips, you end up with a large physical footprint, which implies quantum computers take up a lot of space physically. We can’t currently carry these devices in our backpacks or wear them on our wrists.
The field needs a novel approach to make the capacitors that store the energy that “powers” the qubits in order to shrink qubits while preserving their performance.
We now know that 2D materials may hold the key to making quantum computers possible. 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.
James Hone
Wang Fong-Jen Professor James Hone’s lab at Columbia Engineering has developed a superconducting qubit capacitor manufactured using 2D materials that is a fraction of the size of earlier models in partnership with Raytheon BBN Technologies.
Previously, engineers had to utilize planar capacitors to align the requisite charged plates side by side in order to make qubit chips. Although stacking the plates would reduce space, the metals used in traditional parallel capacitors interfere with the storing of qubit information.
Hone’s PhD students Abhinandan Antony and Anjaly Rajendra sandwiched an insulating layer of boron nitride between two charged plates of superconducting niobium dieselenide in the current work, which was published on November 18 in Nano Letters. Each of these layers is only one atom thick and is kept together by van der Waals forces, which are weak interactions between electrons.
The scientists then paired their capacitors with aluminum circuits to build a chip with two qubits that is 1,000 times smaller than chips made using traditional methods, with an area of 109 square micrometers and a thickness of just 35 nanometers.
The qubits detected the same wavelength when scientists cooled their qubit chip to just above absolute zero. The researchers also saw critical traits that indicated the two qubits were getting entangled and working as a single unit, a phenomenon known as quantum coherence; this would mean the quantum state of the qubit could be modified and read out using electrical pulses, according to Hone.
The coherence duration was just over 1 microsecond, compared to roughly 10 microseconds for a traditionally made coplanar capacitor, although he stressed that this is just the beginning of his research into the usage of 2D materials in this field.
Researchers at MIT used niobium diselenide and boron nitride to manufacture parallel-plate capacitors for qubits in a separate paper published on arXiv in August. The devices investigated by the MIT team had even longer coherence periods, up to 25 microseconds, indicating that performance can still be improved.
Hone and his colleagues will now refine their fabrication procedures and examine various types of 2D materials in order to improve coherence times, which measure how long a qubit can store data.
By merging the elements into a single van der Waals stack or using 2D materials for other parts of the circuit, new device designs should be able to decrease things even further, according to Hone.
“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.”
