Scientists at the National Research University “MISIS”, the Russian Quantum Center and the Karlsruhe Institute of Technology have developed a quantum sensor that can detect defects in the quantum systems. The development could be a step toward the creation of a full-fledged quantum computer. The research was published in the journal npj Quantum Information.
A quantum computer is a device that stores and processes information within a group of quantum systems, each of which is typically a two-level computer called a “quantum bit” or “qubit” (quantum bit). The most popular and promising type of qubit today is considered to be superconducting qubits based on Josephson contacts. Quantum computing devices are most often developed on their basis. It is on Josephson qubits that the quantum processors of technology giants IBM and Google operate.
The key element of superconductor qubits is the Josephson contact, ranging in size from a few tens to a few hundred nanometers. It consists of two layers of a conductor (superconducting metal) separated by a thin dielectric layer, most commonly aluminum oxide.
This method of “assembling” superconducting qubits inevitably leads to so-called two-level defects, which affect their behavior and lead to errors in calculations. This is explained by the fact that modern technology does not allow to achieve one hundred percent accuracy in the creation of qubits. As a result of defects, decoherence – the loss of quantum state by qubits – and the inevitable resulting errors occur.
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Two-level defects in aluminum oxide and on superconductor surfaces are an important mechanism for fluctuations and energy losses in superconductor qubits, thereby effectively limiting the use of such qubits to perform long quantum algorithms.
The more defects arise in the material and the more they affect the qubits, the more errors are produced in the calculations made.
Developed by scientists quantum sensor allows you to determine the exact location and concentration of two-level defects in the cubic chips. According to one of the authors of the study, the head of the laboratory “Superconducting Metamaterials” of the National Research University “MISIS” and head of the group at the RRC, Professor, Dr. Alexei Ustinov, the sensor itself is a superconducting qubit and can detect individual defects and even perform manipulations with them.
As noted by scientists, traditional methods of studying the quality of materials such as X-ray scattering are not too sensitive to small point defects, and their results often do not allow you to understand whether the developers are moving in the right direction in terms of creating better qubits. The proposed approach opens up possibilities for the development of low-loss dielectrics and superconducting materials necessary for the development of quantum computers.
