MIPT: Compact resonators for quantum processors

The main articles are:

• Quantum computers and networks in Russia
• Quantum Computers and Quantum Communications

2024: Building compact resonators to boost quantum processors

For the first time, MIPT scientists showed the reading of a superconducting qubit by a compact resonator, the area of ​ ​ which is about 200x200 μm2, which is 10-20 times smaller than the sizes of coplanar resonators used for this purpose. This size corresponds to the standard size of a superconducting atom. The result can be used in scaling superconducting quantum circuits. The university announced this on May 16, 2024.

source = MIPT

For the practical use of quantum computing, it is necessary to place as many qubits and reading resonators as possible per unit area of ​ ​ the integrated quantum chip. Superconducting quantum chips must be cooled to very low temperatures in special "refrigerators" - dissolution cryostats, the useful space of which is limited. Typical cryostats can house a chip with 100-1000 qubits and service lines, the number of which, in turn, depends on the topology of the chip. Employees of the laboratory of artificial quantum systems MIPT managed to significantly reduce the size of the largest elements of the circuit - resonators serving to read states. Usually, a coplanar resonator is used to read the qubit, the size of which reaches several mm and is determined by the wavelength of the signal used for reading. However, if the resonator consists of separate inductors and capacitances, then the size of these components at the same frequency may be less than the wavelength. It was the resonator of this design that was manufactured and used to read the qubit.

We managed to achieve the compactness of resonators using the technology developed by us of plane-parallel capacitors with a significant electric capacity per unit area. We managed to measure the fluctuations in the probability of an atom being detected in an excited state depending on the duration of the control pulse, which indicates the implementation of reading, "commented one of the authors of the work, Yulia Zotova.

According to the authors, alternative approaches suggest the use of resonators with a more difficult shape to calculate. Their typical dimensions, however, are not small enough (of the order of 0.25 mm2). Technologies related to the formation of 3D structures extending deep into the qubit substrate can also reduce the size of resonators, but are very difficult to use in multi-cube processors.

Another way to reduce the size of superconducting quantum systems is to use acoustic resonators in which phonons interact with a qubit. This work was also carried out at MIPT under the guidance of prof. Oleg Astafiev several years ago.

The results of this work can be used in the future when implementing plans to scale multi-cube processors.