Magnetic flux quantum

Some magnets work in tiny steps. A special ring can hold a magnetic field. This field stays in small bits. Each bit is always the same size.

This happens in a special metal. This metal is called a superconductor. It can hold the tiny bits in a hole. The bits do not change size.

Scientists found this in 1961. It helps us measure things very well. We can use it to find small forces. It is a very neat way to see the world.

Magnets usually work in smooth ways. But in some materials, they work in tiny steps. We call these steps magnetic flux quanta. A quantum is a specific, fixed amount of something.

This happens in superconductors. These are special metals that can carry electricity without losing power. If a superconductor has a hole or a ring shape, it can trap magnetic fields. The field inside the hole cannot be any size. It must be a set of specific amounts. Each amount is one flux quantum.

Scientists first predicted this in 1948. Fritz London was the first to think of it. In 1961, two groups of scientists proved it was real. They found these tiny bits in superconductors.

The size of one quantum is always the same. It uses two big rules of science. It uses the Planck constant and the charge of an electron. This helps us make very good tools. One tool is called a SQUID. It is a very sensitive device that can measure magnetic fields. Another tool uses the Josephson effect. This helps scientists measure electric power with great care.

Magnetic flux is a way to measure a magnetic field through a loop. In most cases, this flux can be any size. However, in some special materials, it can only exist in set amounts. These specific amounts are called magnetic flux quanta. This is a type of quantization, which means something comes in fixed steps. This discovery helps us understand how tiny particles act in large groups.

This phenomenon happens inside superconductors. These are materials that carry electricity without losing any energy. When a superconductor has a hole or a ring shape, it can trap magnetic fields. The field inside that hole cannot be just any strength. It must be a multiple of one specific unit. This unit is the magnetic flux quantum. It is made by combining two big rules of science. It uses the Planck constant and the charge of an electron.

Scientists worked for many years to understand this. Fritz London first predicted flux quantization in 1948. He used a mathematical model to show how it might work. Later, the Aharonov–Bohm effect also helped explain these ideas. In 1961, two different teams proved it was real. B. S. Deaver and W. M. Fairbank found it in a lab. At the same time, R. Doll and M. Näbauer found it too.

There are many important numbers and names in this science. The flux quantum is always the same for any superconductor. Inside a superconductor, particles called Cooper pairs move together. These pairs have a charge of two electrons. There is also a value called the Josephson constant. This is the inverse of the flux quantum. It is used to measure electric potential with great care. Scientists used it to set standards for measurements for many years.

We use these ideas in very sensitive tools today. One famous tool is called a SQUID. This is a magnetometer that can sense tiny magnetic fields. Another important thing is the Abrikosov vortex. This happens in certain types of superconductors. The magnetic field enters the material in tiny tubes. Each of these tubes carries exactly one quantum of flux. These small bits of science help us define how we measure electricity and weight.

Magnetic flux is a measurement of a magnetic field passing through a specific area, like a loop. Usually, this flux can be any value. However, in certain materials, the flux is quantized. This means it can only exist in specific, fixed increments. The basic unit of these increments is called the magnetic flux quantum. This phenomenon is a vital part of quantum mechanics. It shows how tiny quantum rules can affect large, visible objects.

To understand how this works, we must look at superconductors. These are materials that allow electricity to flow without losing energy. Inside a superconductor, particles called Cooper pairs move together. These pairs consist of two electrons working as a single unit. The state of these pairs is described by a wave function called the order parameter. This function has a specific phase, which is like a mathematical angle. In a superconducting ring or a hole, this phase must return to its starting value after one full trip around the loop.

This requirement for the phase creates the quantization. When you calculate the current of the Cooper pairs around a loop, the math shows that the magnetic flux must be a multiple of a specific value. This value is the magnetic flux quantum. It is a combination of two fundamental constants: the Planck constant and the electron charge. Because these constants never change, the flux quantum is exactly the same for every superconductor.

Scientists have a long history of studying these values. Fritz London first predicted flux quantization in 1948 using a mathematical model. Later, the Aharonov–Bohm effect provided further insight into these quantum behaviors. In 1961, the theory was finally proven in a laboratory. Two different teams made this discovery independently. B. S. Deaver and W. M. Fairbank found it, and R. Doll and M. Näbauer found it as well.

Flux quantization appears in different forms depending on the material. In Type II superconductors, the magnetic field does not stay entirely outside the material. Instead, the field enters in tiny tubes called Abrikosov vortices. Each vortex has a core that acts like a tiny hole. This core is a cylinder of normal, non-superconducting material. The magnetic field lines pass through these cores. Each individual vortex carries exactly one quantum of magnetic flux.

This science is incredibly useful for making precise tools. One example is the SQUID, which is a very sensitive magnetometer. A SQUID uses flux quantization to detect extremely small magnetic fields. Another important value is the Josephson constant. This is the mathematical inverse of the magnetic flux quantum. It relates the frequency of irradiation to the potential difference across a Josephson junction. This effect is used globally to provide a standard for high-precision electrical measurements.

Today, these constants help define our entire system of measurement. Before 2019, the Josephson constant helped scientists find very accurate values for the Planck constant. Following the 2019 revision of the International System of Units (SI), many values became fixed. The Planck constant and the elementary charge now have exact, fixed values. This means the Josephson constant and the von Klitzing constant are also fixed. These constants are now primary tools for defining the ampere and other electrical units in science.