Researchers have created superconducting qubits using 2D materials. This opens the door to smaller quantum computers.

Quantum computers must be on the same wavelength as their counterparts, superconducting circuits capable of sustaining an infinite number of binary states. However, this has been at the expense of their size. While transistors in classic computers have been reduced to nanometer scales for superconducting qubits, they are still measured in millimetres. One millimetre equals one million micrometres.

You can combine qubits into larger and more powerful circuit chips. This results in quantum computers taking up a lot of physical space. These devices aren’t yet small enough to be carried in our pockets or worn on our wrists.

The field requires a new method to create capacitors that store energy and shrink qubits while maintaining performance. Professor James Hone recently demonstrated a superconducting qubit caparison at Columbia Engineering in collaboration with Raytheon BBN Technologies. It is made with 2D materials and is a fraction of the size of other capacitors.

Engineers have used planar capacitors to build qubit chips in the past. These plates were charged side-by-side and allowed them to place the required plates. Although stacking these plates would reduce space, the metals in conventional parallel capacitors affect the qubit information storage. The current work was published in the journal NanoLetters on November 18. It is the result of Hone’s PhD students Abhinandan Anthony and Anjaly Rajendra sandwiching an insulating layer made of boron Nitride between two superconducting Niobium Diselenide plates. Each layer is only one atom thick, and they are held together by van der Waals Forces, which is the weak interaction of electrons. Combining their aluminium circuits and capacitors, the team created a chip with two qubits with a surface of 109 square meters and a thickness of 35 nanometers. This is 1,000 times smaller than conventional chips.

The qubits discovered the same wavelength when they were cooled to absolute zero. Hone said that key characteristics showed that two qubits became entangled and acted as one unit. This phenomenon is known as quantum coherence. It would allow for manipulating the qubit’s quantum state and the ability to read it out using electrical pulses. He said the coherence time was very short, at just over one microsecond. This is a far cry from 10 microseconds for a conventionally constructed coplanar capacitor. However, this is only the first step towards exploring 2D materials in this field.

Separate work published by MIT researchers on arXiv in August also used niobium diselenide, boron nitride and parallel-plate capacitors to power qubits. The devices studied by the MIT team showed even longer coherence times–up to 25 microseconds–indicating that there is still room to improve performance further.

Hone and his colleagues will continue to refine their fabrication techniques. They also test new types of 2D materials to increase coherence time, which is how long the qubit stores information. Hone stated that new device designs could shrink things even further by combining elements into one van der Waals stack or using 2D materials to cover other parts.

Hone stated, “We now know 2D materials could hold the key for making quantum computers possible.” Although it is still early, findings such as these will encourage researchers worldwide to explore novel uses of 2D materials. We expect to see more research in this area going forward.