Dr Graham Batey on Low Temperature Physics

When you cool devices to low temperatures then the motion of the electrons and the atoms are greatly reduced and then this simplifies the structure and makes it easy to decide the physics of the device. Dilution refrigerators are very applicable for this application. So this is a really exciting field at the moment People often ask me how cold a dilution refrigerators can actually achieve. If you think of your domestic refrigerators at home in your kitchen then our machines can get something like twenty times colder. My recent work on Chryofree systems has been enormously successful. The original concept of designing Chryofree systems was to basically eliminate liquid helium. It is extremely expensive and requires a lot of expertise to handle it. There is a number of challenges in designing ultra low temperature equipment. We need to first of all have a really good understanding of the physics and the requirements of the machine. There is hundereds of joints well and seals all of which need to be leak tight to an atomic scale. We are running at .01 of a degree above absolute zero. Tiny heat inputs at these temperatures something like one ten millionth of the heat load from an electric light bulb would be too much for the machine to accommodate and it would warm up. In a nutshell, how a dilution refrigerators works is it uses a mixture of two isotopes of helium. It uses helium 3 which is extremely rare and the more abundant helium 4. If you cool down a mixture of helium 3 and helium 4 it will phase separate with the lighter atoms floating on the top of the denser helium 4 atoms. So this is very similar to oil and water. So if you can think of the oil floating on the top and then you have very distinct boundary between the oil and water. If we can force atoms to cross the phase boundary from that concentrated phase to that dilute phase this provides a cooling process. It can operate for weeks or months below ten Milli-Kelvin. I've worked on a number of extremely exciting projects actually over the years. The machines that Professor von Klitzing, Bob Richardson and Doug Osheroff received their Nobel Prize for they were all on machines that I designed. The fascination of working in ultra low temperatures for me and the reason why I really enjoy it is the challenge of achieving the performance the customer requires. It is using my physics education and background to good practical use. Coming up with well engineered solutions and then physically seeing equipment being built from the concept you've designed and it ultimately being it installed in a customer's lab is extremely rewarding. I've been working in the field since 1985 and I still find it very enjoyable.