Today we have two mainstream types of quantum computer: Superconducting Qubits and Trapped-Ions. To make the first type you need (as an absolute minimum) a dilution refrigerator, superconducting qubits and some very fancy control systems. To make the second type you need high vacuum, high voltages, an ion source and some lasers. Trapped-ion quantum computers are generally cheaper to get started with, and indeed I found a really impressive guy on the internet has been building one in his garage. In summary, both mainstream types of quantum computers are very complicated and expensive. Both of these cost way more than $100.

So, what can we build with $100?

We could get some lasers, some diffraction gratings, maybe an LCD or two and some single photon detectors to build a single quantum gate. There are some nice YouTube videos from @LookingGlassUniverse that are well worth a look. This would be very cool, but not exactly useful (and would need to be at least 2m long, unless we use lots of mirrors). Instead, we could build an optical computer. The team from Microsoft Research gave some very interesting presentations at CERN last year as part of the launch of CERN VentureConnect that I was fortunate to follow via Zoom. One of these caught my attention, discussing the use of off the shelf LCD elements for performing large matrix multiplications using light. This we could definitely do for $100 using a Raspberry Pi and hacking a few cheap LCD screens together.

What is the actual project then?

The plan (so far, all plans change!) is to build a very simple optical computer that fits in a briefcase and then use it to do multiplications, and emulate a quantum computer. Simple!

Part 1: Preparation

The team will prepare the hardware, test each component and assemble it in the briefcase.

Part 2: Learning

We will have discussion sessions with experts in the field, including from Microsoft Research in Cambridge, CERN Alumni and the Quantum Photon Science group at the Paul Scherrer Institut (PSI). Students are also encouraged to follow the Qiskit online lectures from IBM.

Part 3: Making it work

Once we have learned about the theory and assembled our computer, we will start with running simple simulations.

The first test will be to run a simple, single pixel multiplication: 0.5 * 0.5 * 0.5 = 0.125. We will need some calibration to know we have the right answer.
After this we can start to increase the resolution of our device, to find out where the limits of its optical performance are (spatially, not temporally)
We will then need to write our own simple simulation of a quantum system, or borrow from someone else's and try to implement this using our new optical multiplier.

Judging Criteria for the Dora Hacks Hundred Dollar Quantum Computer Challenge

Building hardware: 50%
- Can we build an optical computer physically constructed in the box?
Low level code: 20%
- Installing, hacking and enabling all the hardware and drivers to get the physical hardware up and running, exposed to a python environment.
Proof of concept - Optical computer: 20%
- Once the hardware is operational, can we calibrate and operate the optical computer. This is necessary before we can use it for anything. Demo calculations should be performed with good repeatability.
Quantum simulation: 10%
- On the very top of the stack, we need to instantiate a quantum simulation framework. It could be something very simple that we write ourselves, or a more complex open framework that we port from elsewhere. Demonstrate at least one quantum gate.