An international group of Russian and German researchers has made a breakthrough in the creation of materials with properties unattainable in nature. Scientists from the National Research Technological University "MISIS", the University of Karlsruhe (Germany) and the Jena Institute of Photonic Technologies (Germany) under the leadership of the head of the "Superconducting Metamaterials" laboratory of NUST "MISIS" Professor Alexei Ustinov have created for the first time in the world the so-called "mirror" qubits, as well as metamaterial based on them. It is the world's first quantum metamaterial that can be used as a control element in superconducting electrical circuits. The results of the work were published in the journal "Nature Communications".
Metamaterials are substances, the properties of which are determined not so much by the atoms of which they are composed, but by the structures in which these very atoms are assembled. Each such structure (they are called "meta-atom") has dimensions of tens or even hundreds of nanometers and has its own set of properties that disappear when you try to separate it into its components.
Until recently, one of the fundamental differences between atoms and meta-atoms was that the properties of ordinary atoms were described by the equations of quantum mechanics, and meta-atoms - by classical physical equations.
The creation of qubits (the smallest elements for storing information in a quantum computer) has led to the potential for constructing a material consisting of meta-atoms, the state of which is described only quantum mechanically. True, such work required the creation of special qubits.
"An ordinary qubit consists of a circuit that includes three Josephson junctions," explains Kirill Shulga, a researcher at the Superconducting Metamaterials Laboratory at NUST MISIS. - And the composition of the mirror includes five transitions, symmetrical about the central axis. Mirror qubits were conceived by us as a more complex system than ordinary superconducting qubits. The logic is simple: an artificially complicated system with a large number of degrees of freedom has a greater number of factors that can affect its properties. By changing some external parameters of the environment in which our metamaterial is located, these properties can be turned on and off, transferring the mirror qubit from one ground state with some properties to another."
In the course of the experiment, it turned out that all the metamaterial consisting of mirror qubits can switch between two modes. In one of the regimes, a chain of such qubits transmits very well electromagnetic radiation in the microwave range, while remaining a quantum element. In another, it rotates the superconducting phase 180 degrees and blocks the passage of electromagnetic waves through itself. It is important that at the same time it remains a quantum system.
Micrograph of a chain of mirror qubits. In the lower part, the resolution is 20 microns per cm, in the upper part, 5 microns per cm. The circles indicate the Josephson junctions included in one mirror qubit / NUST MISIS Press Service.
“It turns out that with the help of a magnetic field, such a material can be used as a control element in systems for the transmission of quantum signals (individual photons) in the circuits that make up the currently developing quantum computers,” comments Ilya Besedin, an engineer at the Superconducting Metamaterials Laboratory at NUST MISIS … "This is one of the key elements in superconducting electronic devices."
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It is more difficult to accurately calculate the properties of one mirror qubit on an ordinary computer than on an ordinary qubit. By complicating such a qubit several times more, it is possible to reach a limit of complexity that is already close to or exceeds the capabilities of modern electronic computers. Such a complex system can be used as a quantum simulator, that is, a device capable of predicting and simulating the properties of a certain real process or material.
The authors of the study had to sort out many theories in order to correctly describe the processes taking place in the quantum meta-material. The result of these reflections was the article “Magnetically induced transparency of a quantum metamaterial composed of twin flux qubits”, published in the prestigious journal “Nature Communications”.
