The Physical Representation of Qubits

As I’ve been reading more about quantum computing, I’ve been wondering what the physical manifestation of a quantum computer would be. I know what modern-day silicon chips look like, but I have a hard time imagining what a quantum computer would look like. So let’s start at the smallest component — a qubit.

As Wikipedia so helpfully describes, there are many representations of qubits. My simple take-away is that all of them involve very small things — i.e. a single atom, an electron, or a photon. But, these very small things require 1) supercooling (to reduce the noisy state of each qubit), and 2) lasers (to make measurements), and so while each individual element is small, the entire aparatus is large and very complex. Kind of like vacuum tubes and mainframes, in my imagination. As the technology advances, I wonder if it’s even possible for quantum technology to shrink like modern day transistors, since the atomic level is just so different, or if quantum computing will have to be made available through the cloud, only?

I’ve also noticed that different teams are experimenting with different types of qubits and quantum computing: Google and UCSB with superconducting qubits, Microsoft with topological qubits, etc. So it’s not yet obvious that there is a dominant technology or approach in the field.

After skimming the paper from Google and UCSB, I’m still unclear how qubits in general translate to computing work. It seems like after you measure the state multiple times, you get out a probability distribution that the qubit is in any given superposition (extend this to multiple qubits). So while a qubit can be in all of its superpositions at the same time (in real life), as soon as you sample it, you’ve digitized it, or effectively equated the qubit to a normal bit. And therefore, similar to how sampling analog music to create a digital representation loses data, I would assume that sampling qubits to figure out their state must also lose some (valuable?) data…given all the hype, I’m probably missing some key understandings about the field, so I definitely plan to read some more papers and articles. And maybe that is why error correction is so critical in quantum computing?

3 Replies to “The Physical Representation of Qubits”

  1. Part of the answer, it seems to me, lies in the fundamental ability of performing multiple functions in sequence without defining the superpositions and therefore losing the inherent additive data being aggregated/collected.

    You are right, if you collected the data after any logical (I can’t say boolean, so I’ll say qulean) gate, you define the qubit and lose the imaginary portion (pointing to the other potential location(s); that is values), but if you leave the qubit undefined until the answer, an answer is attainable without having to have understanding of the mathematical manipulations leading to that answer.

    Quantum computing, therefore, is using naturally occurring phenomenon that operate by the laws of complex mathematics to perform these complex mathematics without having to conceptualize them or see into the process(es).

    To simplify, it seems to me akin to performing complex math involving multiple variables, but not having to manipulate or even fully know the equations, simply plugging in the value(s) for one (or some) of the variables in the end and getting an answer for a specific outcome. Depending on the outcome (form of the equation; or arrangement of variable(s)) sought, better or worse data can be gleaned. This could be very powerful, allowing for highly complex equations to be solved naturally, and almost immediately.

    1. Hi Andrew, thanks for the comment. What you mention reminds me of this D-Wave primer on quantum computing (linked here), where the system naturally picks “the answer”. Has it been shown that this complex math always finds the “right (best possible) answer”? You mention that better or worse data might be gleaned, so it seems like a quantum system might not always result in the “best” answer?

      I just saw that D-Wave also has a whitepaper with an example quantum program that I want to read through (linked here). But if I understand you correctly, basically, if you give a quantum computer an equation to solve that maps to some real-world question you want answered, it will naturally just settle into the lowest energy state. Then when you take your (final) qubit measurement, you get the answer out, without all the messy, intermediate calculations and steps?? That’s incredible and amazing…it seems quantum programmers need a totally different mind-set and skill-set, to come up with those complex equations, then.

Comments are closed.