More Thoughts on Quantum Computers Becoming a Reality

I wrote a few weeks ago in a previous post about William Halal [1] and when we'll have quantum computers. To summarize: the best guess he's gathered from consulting a bunch of experts is 2021 plus or minus 5 years- which seems reasonable to me.

Current computers where an expensive resource when we first had them. It took decades until they were cheap and practical enough where you could have one at home. I think the same will be true with quantum computers, they'll be very expensive at first. For this reason I see them being a shared resource at first. In other words it will be something that multiple classical computers share. That sharing could be at the institution level, such as a university having some available much like early computers. It also isn't unreasonable to think that processing time could be rented out on it, much like Amazon's EC2.

One obvious question is how the classical computers will interact with the quantum computer. Nearly all proposals for programming quantum computers explicitly or implicitly make use of Knill's QRAM model [2]. In Knill's QRAM model the classical computer is the master and the quantum computer is the slave:

Things get a little more complicated when you throw in multiple classical computers for a single quantum resource. Each of them cannot have full control of the quantum resource and have it function correctly. However, Knill's QRAM model can be expanded to include a "quantum controller" between the classical computer(s) and quantum resource:
This has the advantage that all the logic to deal with the clients can be built into the quantum controller. The controller could also talk to the clients through a standardized protocol, meaning that different physical implementations of quantum computers could still be utilized through the same interface. The controller could also do some other things:

• Queue up requests for operations from a client and execute them at once.
  
• On the fly optimization?
• Deal with disconnected clients at any stage in the computation.
  

The list goes on. Obviously the implementation of this is hard. How exactly do the controller and classical computers communicate for instance? A lot of work would have to go into this, which is why I've listed it as an area for future research in my dissertation. Like programming quantum computers, I think we're best off tackling this issue before quantum computers become a reality outside the lab. Doing so will allow us to hit the ground running with quantum computers instead of stumbling along like we did in the early days of classical computing.

References
[1] W. E. Halal, Technology's Promise: Expert Knowledge on the Transformation of Business and Society, 1 ed. New York, NY: Palgrave Macmillan, 2008.
[2] E. Knill, "Conventions for Quantum Pseudocode," Los Alamos National Laboratory LAUR-96-2724, 1996.

William Halal on Quantum Computing

William Halal published a book titled "Technology's Promise: Expert Knowledge on the Transformation of Business and Society" in 2008 [1]. (You can find it here on Amazon.) I had read an early draft of the book in the summer of 2007 prior to a presentation he did at Colorado Technical University's Institute for Advanced Studies.

Quantum computers currently don't exist outside the lab. What we do have in the lab doesn't consist of more than a few handfuls of qubits. This is because physically implementing quantum computers is a very hard task do to decoherence. In other words the system must be isolated from the outside environment. If the qubits interact with the outside environment then it is an observation and the system will "collapse" out of superposition and yield a classical result.

Given the difficulty in implementing quantum computers, there are a wide variety of guesses on when and if they'll become available. I've heard everything from we have them now (D-Wave systems) to we'll never have them.

What William Halal has done is utilize the work of the TechCast project to gather the opinions of 100 experts to come up with best guesses. (These experts are gathered from around the world.) According to this, he lists that "...quantum computers are likely to become available about 2021 +/- 5 years" in "Technology's Promise".

I think the prediction of 2021 is a reasonable one. This still gives us 12 years to overcome the challenges of creating them, which is quite a long time in technology. I wouldn't be too surprised if some hurdles pushed us out a few years, but I also wouldn't be surprised if we made some leaps that also rained the date in a few years. In any case, I expect to see some big advances toward making quantum computing a reality in the next decade or two.

References
[1] W. E. Halal, Technology's Promise: Expert Knowledge on the Transformation of Business and Society, 1 ed. New York, NY: Palgrave Macmillan, 2008.