Exploring Quantum Computing: Making a Qubit with Josephson Junctions

[Robin_Shorrosh]

I am working on a project for our local science fair and decided on researching quantum computers. (This is what my focus will be in college.) Though, I expect to work on this far past the time allotted for that. I would like to build a superconductor based qubit using Josephson Junctions. The main goal is to be able to measure electron spin of an atom and won’t be capable of programing. This seemed somewhat plausible as I have a mentor at our local university as well as lab access, a liquid helium dewer and most of the supplies. The problem arose when I mentioned material deposition to create the junction as we would not have access to that. So my question is: What other options are there for doing this? His focus is in material physics and so he has the most experience with super conductors and hence my research has been too. Would a photonic system be more plausible to test? Also for the fair, any ideas on a simpler experiment that could be created and tested with the 2 month time limit relating to the subject? Thanks in advance!

 

[f95toli]

Does your mentor already work in this field? If so, I would suggest you discuss this with him/her a bit more. From your description I can tell you need to read up a bit more about his field.
Firstly, I don't know how you would measure the "spin of an atom" using a qubit(?); meaning it is not clear what type of experiment you have in mind. I can think of a few related experiments, but no one has yet -as far as I know- managed to couple a qubit to a single spin (i.e. an ion, NV centre or somethign similar), the experiments that have been done use 10^11 spins or so.
Secondly, making qubits is HARD and you need a lot of expertise and a lot of equipment (btw, liquid helium is not nearly cold enough, you need a dilution refrigerator to measure superconducting qubits) so it won't be feasible as a two-month project.

Could you do something else QC related? If you want to do a theory project there are some relatively easy to use software packages out there

 

[Robin_Shorrosh]

Thanks for the reply. That was my mistake; I meant to say the spin of an electron of an atom, not the atom itself. We would add an atom (he recommended phosphorus) into a silicon wafer. When cooled the superconductors would force the electron into a spin down state. We would then use microwaves (set to the resonance frequency of the electron) to put it into the spin up state and measure with an oscilloscope. It would not be a true "qubit" rather a study of the principle behind it. As far as the fridge goes, the university has one (helium 3 and helium 4 based as I mentioned earlier.)They told me it could cool the particle to below .04K. This will defiantly be a long term project but for the software, what packages are you referring to? Is it in the scientific Linux distro? Regardless this should be a great learning experience!

 

[f95toli]

When you say "superconductor" what do you mean? A superconducting resonator?
Is this what you have in mind?
http://arxiv.org/abs/1508.06148

Note that they are -as I mentioned above- coupling to a large ensemble of ions in the silicon; NOT a single spin

Regardless, it is still way to ambitious. There are lots of technical issues that you need to overcome in order to do this type of work. You wouldn't be able to do this in two months even if you were an experienced senior researcher; even just fabricating a sample would take a couple of weeks and that is assuming you know exactly what you are doing and have access to a suitable cleanroom.

I should mention that this is one of the fields I work in (I have a PhD student investigating a hybrid superconductor-ion system) so I know very well just how difficult this is (i.e. I actually know what I am talking about, for once)

The software package I had in mind is Qutip (http://qutip.org/), It is fairly easy to use, and you don't need to know that much about Python to use it,
Note that I am NOT suggesting trying to create a model from scratch (that would be too complicated), but you can download and modify some of the example that comes with Qutip. This would e.g. allow you to experiment with models of a single spin/qubit (which could be e..g P in silicon if you enter the right parameters ) coupled to a superconducting resonator.