Comprehensive coverage

Quantum flow circuits

Researchers have built a component that amplifies quantum signals that can be used to upgrade quantum computing capabilities

A quantum computer, which many scientists aspire to develop, will be based on quantum mechanics - a physical theory that describes the behavior of nature on a very small scale. That is, the world of particles. The leading infrastructure of quantum computing is superconducting electric circuits (which conduct electric current without resistance), and its main operating principle is superposition - a quantum phenomenon in which one system can be in two states at the same time. In the quantum computer, this system is the qubit - the quantum bit - which can be both 0 and 1 at the same time (as opposed to bits in a normal computer which can be in one state of operation at a time, 0 or 1). It therefore has enormous potential computational power.

What is the question? How can the information that passes through the quantum computers be preserved?

Prof. Nadav Katz from the Faculty of Mathematics and Natural Sciences at the Hebrew University researches information processing and storage in quantum computing systems. In doing so, he develops basic components of quantum computers and examines their properties and the materials from which they are composed. According to him, "The processing and preservation of information in quantum computing - such as the electrical flow of electrons in a circuit, for example clockwise, counterclockwise or simultaneously (as a superposition) in both directions - depends on the quality of the components. In my research, I am examining new type of components, superconductors that can replace those currently used in quantum computing, that have properties that can contribute to the transmission of quantum information and minimize errors in this process." In the upper figure: the quantum amplifier built by the researchers - a layer designed to a nanometric structure of the tungsten-silicon superconductor (brown) on a silicon substrate (grey) and on top of that a nanometer insulating layer of amorphous silicon (orange) and a superconducting aluminum layer (light blue). In the lower figure: the amplification of the quantum signals

In their latest study, which won a research grant from the National Science Foundation, Prof. Katz and his team sought to replace the Josephson junction - a central component in the infrastructure of any superconducting quantum computer - with simpler quantum (superconducting) components. The Josephson component consists of two aluminum units (superconductors) with a thin layer of oxide (insulating material) between them. The possibility of replacing it with other components arose because many times the quantum information gets messed up inside the oxide. For example, the superposition is destroyed and noises are caused that damage the quality of the quantum state over time. That is, the disadvantage of this component harms the ability to build advanced quantum computing.

In the upper figure: the quantum amplifier built by the researchers - a layer designed to a nanometric structure of the tungsten-silicon superconductor (brown) on a silicon substrate (grey) and on top of that a nanometer insulating layer of amorphous silicon (orange) and a superconducting aluminum layer (light blue). In the lower figure: the amplification of the quantum signals
In the upper figure: the quantum amplifier built by the researchers - a layer designed to a nanometric structure of the tungsten-silicon superconductor (brown) on a silicon substrate (grey) and on top of that a nanometer insulating layer of amorphous silicon (orange) and a superconducting aluminum layer (light blue). In the lower figure: the amplification of the quantum signals

In accordance with this, the researchers built a new component, a superconductor that consists of tungsten metal (wolfram) and silicon and makes it possible to create quantum flow circuits. They designed it using lithography, layer digestion and deposition methods. Thus, through the evaporation of the materials and nanolithographic production processes, they created a structure of a quantum-limited microwave amplifier and placed it on a silicon chip. "We chose these materials because they are known detectors of optical photons. We hoped that they would be able to function in the circuits that make up quantum computing," explains Prof. Katz.

The researchers implemented the component in a model of a quantum computer with a small number of qubits, placed it near the qubits and found that it amplifies quantum signals 100 times their original strength. Quantum signals are, for example, microwaves (photons) that are trapped and move in the chips of the computer and progress from point to point. When they are amplified, the qubits can be measured and thus examine the state of the quantum computer. According to Prof. Katz, "the measurement of qubits is an essential part of the characterization of quantum computing, its use and the information that passes through it, and is mainly based on the amplification of quantum signals. Therefore, we created a quantum amplifier that can upgrade this computing capabilities."

The researchers built a new component, a superconductor that makes it possible to create quantum flow circuits. They designed it using lithography methods, thus creating a structure of a quantum wave amplifier.

The researchers also discovered that under certain operating conditions the new component can transmit microwaves with quantum entanglement - a phenomenon in which two separate bodies can express a strong correlation even without exchanging information between them, which enables accurate and sensitive quantum measurements. Therefore, they hope that this component will also be used in the future for measurements and transmission of information and quantum encryption of a new type.

Life itself:

Prof. Nadav Katz, 46 years old, married + four, lives in Jerusalem. Environmental activist in a variety of channels (with an emphasis on green energy), including the Israeli Energy Forum. Likes to travel, read science fiction, biographies and philosophy, listen to classical music and solve logic puzzles.

Another son