The team's chip is 1000 times smaller than others made with conventional fabrication techniques. Credit: Columbia Engineering.
For quantum computers to surpass their classical counterparts in speed and capacity, their qubits need to be on the same wavelength. The cost of size has made this possible. One millimeter is one million nanometers, and the qubits used in classical computers are still measured in millimeters.
When you combine qubits together into larger and larger circuit chips, you end up with a big physical footprint, which means quantum computers take up a lot of physical space. We can't wear these on our wrists or carry them in our backpacks.
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. Professor James Hone's lab at Columbia Engineering recently demonstrated a qubitCapacitor built with 2D materials that is a fraction of previous sizes.
Engineers have had to use planar Capacitors to build qubit chips. The metals used in parallel Capacitors interfere with qubit information storage, so stacking those plates would save space. The current work was published in the November 18 edition of the journal. These layers are held together by van der Waals forces and are just a single atom thick. The team combined their capacitors with aluminum circuits to create a chip with two qubits that is just 35 nanometers thick and is 1,000 times smaller than chips produced under conventional approaches.
The qubits found the same wavelength when they were cooled to just above absolute zero. Hone said that the team observed that the two qubits were becoming entangled and acting as a single unit, a phenomenon known as quantum coherence, which would mean that the qubit's quantum state could be manipulated and read out. He said that the short coherence time was a first step in exploring the use of 2D materials in this area.
In August, researchers at MIT published separate work on arXiv that used niobium diselenide and boron nitride to build parallel-plate capacitors for qubits. The devices studied by the MIT team showed longer coherence times of up to 25 microseconds.
Hone and his team will continue refining their fabrication techniques and test other types of 2D materials to increase coherence times, which reflect how long the qubit is storing information. Hone said that new device designs should be able to shrink things down even further by combining elements into a single van der Waals stack or by using 2D materials for other parts of the circuit.
