Continue to cool in "magnetic cup"

However, the laser method can only cool the atoms up to about 1/1000000 at most, far less than the temperature required by Bose Einstein condensation. The second step is to continue to cool the atoms by evaporative cooling.

To understand this method, let's first observe how a glass of hot water gets cold. Hot water in a teacup is made up of many water molecules. The energy of these water molecules is large and small. Because the energy of the water molecules moves fast, they quickly run out of the cup and turn water vapor into the air. In this way, as the energy of the water molecules gradually run away, the temperature of the water will gradually become colder. If we also have an atom cup to hold the atoms in, then if there is enough time, the atoms in the cup will cool to enough low temperature.For Bose Einstein condensation, the cup we use is made of magnetic field. The atoms are placed in this "magnetic cup" for evaporative cooling, which is called magnetic trapping trap.

We know that the atom itself is magnetic, like a small magnetic needle. We can design a very strong magnetic field, imprisoning atoms like a well and isolating it from the outside world. In this way, the atoms with high energy will gradually escape from the well edge and the atoms will gradually cool down. Of course, this process is very slow. If we reduce the height of the well, the cooling rate will accelerate.

In fact, in the Bose Einstein condensation experiment, it is through increasing the height of the well gradually to accelerate the cooling rate. Of course, this speed must be well controlled. Because the speed is too fast, the atoms that finally reach Bose Einstein condensates will be too few. By carefully controlling the velocity, most of the atoms can reach the Bose Einstein condensate in a relatively short time.

Through these clever masters, physicists finally realized their dreams for decades. In 1995, Connell and Weinman first made about 2000 rubidium atoms at the temperature of 0 00002k to achieve Bose Einstein condensation. Subsequently, he used sodium atoms to do the same experiments. The experiments he designed can make more atoms reach Bose Einstein condensates, so we can do more in-depth research on this strange state. He also used two "super atoms" to get very clear interference fringes, just like the interference fringes produced by two laser beams.

Their success has raised the climax of Bose Einstein condensation in the world. Now, around more than 30 laboratories in the world have successfully realized Bose Einstein condensation, and the condensed state of lithium and potassium has recently been obtained. In addition to alkali metals, French scientists first made the Bose Einstein condensate of helium atoms not long ago. Progress in experimental technology has also been very rapid. Scientists have recently developed a very small chip that allows atoms to reach Bose Einstein condensate in a very short time. This achievement will enable more laboratories to join the research in this field.