Here is a picture of the new experimental setup:
In this picture we are testing that the apparatus cools down OK. This type of fridge is an Oxford Instruments Heliox, which is a He-3 based cooling system. The principle of operation is that you cool a ‘plate’ of metal to 1.5K by pumping a small amount of liquid from the main He-4 bath. The low pressure causes the He-4 to rest at this lower temperature instead of 4.2K. The cold plate is then brought into contact with He-3 gas, which condenses and drips down into a ‘pot’. Once you have condensed all the gas, you then pump on the He-3 pot itself (in the same way that you did with the He-4), which causes the liquid to slowly evaporate and cool as its tries to equilibrate its vapour pressure with the partial vacuum you create. However, unlike He-4, He-3 cools to much lower than 1.5K. In fact the temperature can be maintained at ~250mK for up to 90 hours, and you can supply extra heat to get a stable temperature anywhere up to around 1K.
This apparatus will be used to measure further interesting properties of unconventional pi-Josephson junctions at low temperatures. These junctions will (hopefully) eventually be of use in quantum computing applications: A built in phase shift across the junction gives rise to a degenerate ground state at zero applied flux, removing the need for application of a flux bias to obtain the qubit working point (a superposition of macroscopic quantum states).
With this one going too, it means I’ll be running 2 experiments (MQT on the dilution fridge and conductance on the CF), helping run this one (300mK heliox system), and building another (second dil fridge wiring for co-planar resonator coupled to qubit stuff) all at the same time. Argh! Still, lots of fun to be had.
For additional food for thought here is a delightful cake. A chocolate orange cake in fact. I made this one at the weekend. Excuse the quality of the photos, I only had a phone-cam at the time.