Normally, two electrons repel each other because of Coulomb's law. However, in a superconductor they attract each other and pair up due to interactions with the material in which they reside. This allows the electrons to flow without resistance - in principle such a current of electrons can flow forever - and is an example of an effective interaction and pairing which lead to very unusual material properties. While a room-temperature superconductor would lead to major technological advances, it remains a distant dream after more than a century of research. Indeed, the highest temperature superconductor experimentally achieved so far was at -138 degrees Celsius, colder than any place on earth outside the lab! This illustrates the need for a fresh approach in order to understand the mechanisms of superconductivity, effective interactions and pairing.
Fortunately, it is possible to mimic the electron behaviour in superconductors and a very versatile candidate for this simulation is a cold atomic gas. Here, a typical experiment will contain about a million atoms in a small volume of space less than a millimetre across and at a temperature extremely close to absolute zero. What makes cold atomic gases special is that they are extremely clean - they only contain the atoms put there by the experimentalist, and they can be easily manipulated by lasers and magnets. For instance, a set of lasers can be used to squeeze the atoms so that they move only in a plane, fundamentally changing the nature of the gas, and the study of this system may yield insights into some superconductors in which the electrons also move in a plane. In this way, a cold atomic gas may simulate aspects of a complicated material in a very controlled manner, yielding a greater understanding of the material properties.
Levinsen's research is encompassing several areas of cold atomic gases, for instance heteronuclear mixtures of heavy and light atoms interacting with short ranged potentials, where the light atoms act to provide an effective (near-resonant) long-range interaction between heavy atoms. He is also working on dipolar gases of micro-wave dressed fermionic molecules, where the long-range nature of the dipolar interaction can be used to suppress losses, while simultaneously resonantly enhancing the critical temperature of superfluidity. A common feature among these systems is that they display unusual effective interactions which lead to non-trivial pairing mechanisms. The goal of Levinsen's research is to study these effective interactions and provide fundamental insights into how these affect the large-scale system properties.
Jesper Levinsen is a Dale T. Mortensen Junior Fellow at AIAS. He received his bachelor's and master's degrees in physics from the University of Copenhagen, before moving to the University of Colorado at Boulder for his PhD. Following post doctoral fellowships at the Université Paris-Sud XI and the University of Cambridge, he recently arrived at Aarhus University. His research focuses on ultracold atomic gases, with particular emphasis on the properties of strongly correlated systems. During his DTM Fellowship, he will be working with the project “Engineering novel quantum phases with cold atoms”.