Scientists create superconducting quantum refrigerator

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Quantum Refrigerator
The superconductor fridge is similar to a conventional refrigerator, in that it moves a material between hot and cold reservoirs. However, instead of a refrigerant that changes from a liquid state to a gas, the electrons in a metal change from the paired superconducting state to an unpaired normal state. Credit: University of Rochester illustration / Michael Osadciw

Imagine if we can think of a refrigerator so cold that it could turn atoms into their quantum states giving those properties that defy classical physics rules. In a paper published in Physical Review Applied, Andrew Jordan, physics professor at University of Rochester, and graduate student Sreenath Manikandan, along with other scientists put forward an idea that would cool atoms to nearly absolute zero temperatures and would be based on the quantum property of superconductivity which can be used to enhance the performance of quantum sensors for ultrafast computing.

The ability of a metal to conduct electricity is called conductivity. A metal with high conductivity allows electric current to flow through and offers negligible resistance to the flow of electrons. A superconductor is a scenario where the material would conduct electricity without encountering resistance and current would circulate indefinitely without any resistance. When you cool down electrons to extreme temperatures, electrons flow like a fluid without resistance. This is possible due to Cooper Pair formation at low temperatures. When you reach such low temperature, the resistance abruptly drops to zero and there is a phase transition that occurs.

Researchers could then change material into a superconducting state which is similar to material in solid, liquid or gaseous state. The operating principles of these refrigerators are quite similar to that of traditional refrigerators as both use a phase transition to get the cooling power required.

A conventional refrigerator is usually hot on the backside and operates by removing inside heat by moving a fluid called refrigerant between hot and cold reservoirs by changing the state from liquid to gas. The refrigerant in liquid form passes through expansion valve due to which there is a drop in pressure and temperature due to gaseous form. It passes through the coils absorbing heat from the system. It is again compressed into liquid by the compressor and radiating absorbed heat and the cycle is repeated however in a superconducting refrigerator instead of using a refrigerant, the electrons in the metal changes from the paired superconducting state to an unpaired normal state.

In a superconducting quantum fridge, researchers placed a layered stack of metals in a cold dilution refrigerator. The bottom layer is a sheet of superconducting niobium, the middle layer is the superconductor tantalum and the top layer is copper.

Researchers applied a current of electricity to niobium which generates a magnetic field that penetrates the layer of tantalum causing unpairing of superconducting material and causing cool down. The cold tantalum layer absorbs heat from the warmer copper layer. The magnetic field is slowly turned off causing tantalum to pair up again which causes tantalum to become hotter than niobium. The cycle repeats again which maintains a low temperature in the topmost copper layer.

 

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