Breaking the monopoly, my country's first dilution refrigerator for quantum computers is launched! How does superconducting technology change the world?

On February 26, Anhui Quantum Information Engineering Technology Research Center and KUST Guodun Quantum Technology Co., Ltd. jointly announced that the domestically produced dilution refrigerator ez-Q Fridge completed performance testing, showing that the actual operating indicators of the device reached the international mainstream level of similar products, becoming the first commercially available and mass-produced dilution refrigerator for superconducting quantum computers in China. Dilution refrigerators are key core equipment for building superconducting quantum computers. The development of superconducting computers is inseparable from superconducting materials, and usually requires low temperature conditions for equipment to operate. So what are superconducting materials, and what is low temperature operation? Let us get closer to superconducting materials and understand its past and present.

To understand superconducting materials, we have to start with the superconductivity phenomenon. In 1911, Dutch physicist Onnes cooled metal mercury to below 4K (K is Kelvin temperature, 4K is approximately equal to -269.15℃), and found that the resistance was almost reduced to zero. This is the origin of the superconductivity phenomenon. Subsequently, the study of superconducting materials became a hot topic. In 1933, German physicist Meissner discovered that when a magnet and a superconductor are close to each other, a superconducting current will be formed on the surface of the superconductor under the influence of the magnetic field of the magnet. The magnetic field generated by the superconducting current is equal in magnitude and opposite in direction to the magnetic field generated by the magnet inside the superconductor. After the two are offset, the magnetic induction intensity inside the superconductor becomes 0, which means that the superconductor has antimagnetism. This phenomenon is called the Meissner effect. In 1962, Josephson studied that after two superconductors were separated by a thin insulating medium, a voltage was applied at both ends of the material, and electrons would pass through the insulator from one end to the other superconductor, as if there was a tunnel between the superconductor and the insulator. This phenomenon is called the tunnel effect. When the voltage is removed, the magic happens again. There is still a weak current between the two superconductors. This is the Josephson effect of superconductors. Simply put, superconductors have three characteristics: zero resistance, Meissner effect, and Josephson effect. As the name suggests, superconductivity means that electrons can flow freely in a metal, alloy, or compound material at a certain temperature, that is, the resistance is zero.

So, what is the certain temperature condition? Superconducting materials are divided into low-temperature superconducting materials and high-temperature superconducting materials. But the high and low temperatures here are not the high and low temperatures we understand in our daily lives. The critical temperature of low-temperature superconductors is lower than 25-30K, and the critical temperature of high-temperature superconductors is higher than 25-30K. The coolant of low-temperature superconductors is liquid helium, and the temperature is below 4.2K. The coolant of high-temperature superconductors is liquid hydrogen and liquid nitrogen. But why does the superconductivity phenomenon occur? In 1957, the theory proposed by Bardeen, Cooper, and Schrieffer was the first to reveal the cause of the superconductivity phenomenon to the world. This theory understands the superconductivity phenomenon as a macroscopic quantum effect. The theory points out that two electrons with opposite spin and momentum in superconducting materials can pair up to form "Cooper pairs". In an ultra-low temperature environment, "Cooper pairs" do not exchange energy with the electron lattice, and can move without loss in the lattice, that is, the resistance disappears, and a superconducting current is generated. The main representatives of low-temperature superconducting materials are niobium titanium alloy (NbTi), niobium tin alloy (Nb3Sn), niobium aluminum alloy (Nb3Al) and other alloys, but because low-temperature superconducting materials require expensive liquid helium environment, their application is limited. High-temperature superconducting materials can be used in cheap liquid nitrogen refrigeration environment, and the main representatives are yttrium barium copper oxide (YBCO), bismuth strontium calcium copper oxide (BSCCO) and other compounds.

Scientists believe that superconducting technology can change the world. So, what are the specific applications of superconducting materials?

Superconducting magnets are the most widely used field for superconducting materials, and they have many uses in the medical field. In the nuclear magnetic resonance imaging technology of medical testing, a strong magnetic field environment is required for patient testing. Superconducting coils made of superconducting materials have the characteristic of zero resistance, and the current can generate a strong magnetic field to meet this requirement.

Large scientific research equipment, such as high-energy particle colliders and particle accelerators, cannot do without superconducting magnets. Electric energy transported through traditional wires cannot avoid the problem of resistance energy consumption, and about 10% of the electric energy will be wasted in the form of heat. The zero resistance characteristic of superconducting cables can effectively avoid energy loss and save 40%-80% of energy compared to ordinary cables.

Superconducting computers are an important research direction in the computer field in the 21st century. Superconducting computers based solely on simple superconducting devices can execute 50 billion instructions per second, which is 100 times faster than the fastest silicon-based materials currently available.

By utilizing superconducting technology, superconducting quantum interferometers can be manufactured for weapons and equipment, demonstrating the ability to identify the surrounding magnetic field and its sensitivity. It can also be used to manufacture superconducting infrared detectors, as well as superconducting electromagnetic propulsion systems, superconducting tanks, superconducting aircraft, superconducting space launchers, etc.

The applications of superconducting materials are by no means limited to these. Humans have never stopped exploring superconducting materials, and superconductors are showing a thriving development trend. Looking back over the past century, superconducting technology has already influenced the world, and there is still a broad space for research to benefit all aspects of human life.

(Mo Zunli is a professor and doctoral supervisor at Northwest Normal University, and Lv Wenbo is a master's student at Northwest Normal University)