World’s first switchable quantum metamaterial investigated
The team of researchers from the Leibniz Institute for Photonic Technologies in Jena (Leibniz-IPHT), the Karlsruhe Institute of Technology (KIT) and the National University of Science and Technology (NUST MISIS) in Moscow produced for the first time a quantum metamaterial that interacts in a special way with electromagnetic radiation in the microwave range. The metamaterial consists of a linear array of 15 meta atoms, the quantum bits or qubits: loops of aluminum with a diameter of a few microns, which, at their operating temperature close to absolute zero, transport electrical current superconducting and thus loss-free. At some points, the aluminum rings are interrupted by a few nanometers of thin tunnel structures, the Josephson contacts. This results in superconducting oscillating circuits in which current flows only in two defined states.
For the first time, the researchers have now constructed a meta-material from so-called twin qubits, which consist of two interconnected loops and thus have five Josephson contacts instead of three. The structures were created in the clean room of the Leibniz-IPHT. “We investigated how the twin qubits behave when they are brought into two different states by means of a magnetic field,” says Leibniz-IPHT scientist Prof. Evgeni Il’ ichev, describing the discovery. “The metamaterial showed an unexpected property to us. The magnetic field enables us to precisely control its transmittance for radiation in the microwave spectrum. We were surprised that the transparency of these special quantum metamaterials can be switched on and off by configuring the basic state of the qubits. This was previously unknown,” Il’ ichev said. The research results, which were developed under the direction of Prof. Alexey Ustinov (NUST MISIS), were published in the journal Nature Communications.
Unlike the units (bits) of a classic computer, the qubits do not only assume the binary states 0 and 1. They obey the laws of quantum mechanics and are in a superimposed state, which is 0 and 1 simultaneously. In the case of superconducting qubit circuits, the magnetic field-induced current flows simultaneously left (0) and right (1). However, the superimposed states exist only until they are measured – at this moment the system assumes either 0 or 1. Due to the superimposition states, quantum computers can process a large number of computational operations in parallel, while today’s computers perform them one after the other. The number of operations increases exponentially with the number of qubits used. IBM offers online access to a superconductor-based quantum computer with 20 qubits.
The Leibniz-Institute for Photonic Technologies (Leibniz-IPHT) researches the scientific basis for photonic processes and systems of highest sensitivity, efficiency and resolution. In line with the motto “Photonics for Life – from ideas to instruments”, scientists at the Leibniz-IPHT develop tailor-made solutions for questions in the fields of life sciences, environmental sciences and medicine.