I gather that this has something to do with with error correction in the crazy world of quantum computing.
Given that I don’t understand QC, it stands to reason that I don’t understand QEC in any detail.
Still, you can’t throw a term like “cat qubits” around and expect me to not be curious. : – )
So, I had to look at a report from a French group, “Quantum computation with cat qubits” [1].
I gather that a cat qubit is a system that deals with error correction in the crazy world of quantum computing. Quantum Error Correction (QEC) is a difficult engineering problem for constructing useful quantum computers. If it takes too much time and resources to detect and correct random errors, it doesn’t matter how fast the (error prone) computation is, it’s impractical. Hence, QEC is vital to useful QC.
There has been quite a lot of theoretical and experimental work using this kind of “cat code”. (Of which I understand not one whit.) I gather that these use “cat states” to encode information. This is an example of a Bosonic Code (which would be a great name for a band), which, to quote the Wikipedia article ,“bosonic codes encode information in the infinite-dimensional Hilbert space of a single mode.” (No, I don’t know what that means.)
First, even a dumb old software guy like me was able to figure out that “cat qubits” refers to Schrödinger’s cat, which is famously, either alive or dead, or, alternatively, both alive and dead, until we open the box.
So the goal of a cat qubit is to have a qubit that is either “1” or “0” when it is observed (the box is opened). And, from an engineering standpoint, this should be a fast and cheap process end to end –at least, I think that’s what it means.
As far as I can tell, the basic idea in this paper is a straightforward use of the concept of parity bits that is familiar to non-quantum computing. Adding extra, redundant bits costs hardware and time, but logically makes it possible to quickly and reliably detect errors. In the quantum version, extra qubits encode redundant bits, and reading out the qubits yields the value of the encoded bit even in the case of a 1 bit error.
The paper focusses practical engineering issues, i.e., “paving the way towards hardware-efficient implementations of a fault-tolerant quantum processor.” ([1], p. 13) Their approach is notable because it operates autonomously, automatically suppressing bit flipping errors, giving an error free bit every time.
OK, that last part is beyond magic to me, its magic to the magic power. : — )
- Jérémie Guillaud, Joachim Cohen, and Mazyar Mirrahimi, Quantum computation with cat qubits. arXiv, 2023. https://arxiv.org/abs/2203.03222
PS. As always, anything quantum provides many great names for bands. Here’s a few from this paper:
- Bosonic Code
- Decoherence
- Bit-flip code
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