טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentLevy Shahar
SubjectMeasurement of the A.C. Josephson Effect in a
Bose-Einstein Condensate
DepartmentDepartment of Physics
Supervisor Professor Jeff Steinhauer
Full Thesis textFull thesis text - English Version


Abstract

In 1995 the first Bose-Einstein condensation (BEC) in dilute atomic gases was realized. Unlike other BEC's (superconductor and  superfluid), in this type of system many physical parameters, such as interaction strength, density, size, spatial configuration, external potential etc., can be controlled. This fact made the BEC of dilute atomic gases an important tool in the field of many body physics.


The Josephson effects describe the behavior of two adjacent condensates separated by a tunneling barrier. They predict unique behaviors of the tunneling current through the barrier. One such behavior is the presence of an oscillating tunneling supercurrent when a constant potential difference is applied. A detailed analysis of this phenomena indicates that the oscillation frequency depends linearly on the potential deference, independent of any other system parameter or configuration. This is known as the a.c. Josephson effect. Another peculiar dynamics between these two adjacent condensates is known as the d.c. Josephson effect. In this case a constant supercurrent tunnels through the barrier although no chemical potential difference exists between the barrier's both sides. It is as if water will pass from one container to another, although no pressure difference exists between the two containers. A third effect related to this two condensate configuration is the Macroscopic Quantum Self Trapping (MQST). Here the chemical potential difference between the two condensates is retained through time, although a current can flow between the two condensates. It is as if you connect the two sides of a charge capacitor and it doesn't discharge.


All the above intriguing phenomena are the result of the quantum nature of the many body system we are dealing with. Studying the Josephson effect is thus in the heart of understanding the physics of many body system: the ideas of macroscopic phase, interference behavior, order parameter etc.


In our laboratory we observed these three phenomena: the a.c. Josephson effect, the d.c. Josephson effect, and the MQST effect. We are the first to observe the a.c. and d.c. Josephson effects in BEC of dilute atomic gases. We were also the first to measure the effect of thermal atoms on MQST.


In this thesis I shall describe the experiment we conducted to observe the a.c. Josephson effect.