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I notice numerous companies and research groups around the world trying to build QC's with wildly different approaches. Intuitively, this suggests to me that QC is still very early in its maturation - we are far from certain as to how to actually build one. I see groups using ultracold gases, solid state qubits, etc etc.

Could someone offer a high level overview of the pros and cons of the following approaches:

  1. Superconducting qubits
  2. Solid-State qubits (using Quantum Dots)
  3. Ion trapping
  4. Neutral atom trapping

Why is say, Google or Amazon, so intent on investing in superconducting based QCs while Mikhail Lukin or ColdQuanta spend millions on neutral rydberg atoms while Silicon Quantum Computing in Australia is using Quantum Dots? If I've missed important "paradigms" or architectures, don't hesitate to include them in your answer.

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  • $\begingroup$ Hi and welcome to Quantum Computing SE. Could you please make your question narrower? To compare so many technologies seems to be too broad. You can ask e.g. for papers containing comparison of the technologies. $\endgroup$ Aug 15 at 10:29
  • $\begingroup$ Posting a paper would be a valid answer so I don’t see why the question is too broad. It is much more efficient to post one question than the same question over and over for each architecture. I’m looking for an answer to my question so if a paper answers it then my question has been answered and all future viewers can go straight to a paper addressing this question. This question is also good for the sake of public understanding of quantum computing. If you want something more focused then I’ll take this question elsewhere. Such a question would generate a lot of attention for this community $\endgroup$
    – Andrew
    Aug 15 at 10:38
  • $\begingroup$ You might find section 5.2.2, 5.3.2 and 5.4 as well as appendix B, C and D of this book useful (honestly you might find the whole book useful too!) nap.edu/catalog/25196/…. $\endgroup$ Aug 16 at 10:46
  • $\begingroup$ @RajivKrishnakumar Thank you! $\endgroup$
    – Andrew
    Aug 17 at 1:32
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The major quantum computing providers that comes to me right the way are usually:

  1. IBM Quantum (superconducting qubit)

  2. Google Quantum (superconducting qubit)

  3. Honeywell Quantum (trapped ions)

  4. Rigetti (superconducting qubit)

  5. IonQ (trapped ions)

The players in this list are primarily focus on two technologies, superconducting and trapped ions. Note that there are different type of superconducting qubits too.

I think the below two papers will be useful in the discussion about the pros and cons of each of the technologies above.

1. Trapped-Ion Quantum Computing: Progress and Challenges

----> Page 3 discuss pros and cons

2. Superconducting Qubits:Current State of Play

----> (see page 12 for pros, page 22 for current and near term challenges)


Additionally, this lecture slides on superconducting qubit might also be helpful. Here is a screenshot of the pros and cons slide: enter image description here

This other paper, Analysis on the Mechanism of Superconducting Quantum Computer, also talks about the pros and cons of superconducting qubits. See the last part of the paper, which I added below for convenient:

3.1.Advantages: The most essential advantage of the superconducting computer is that it fits well with the current microelectronic processing technology. The core circuits of charge qubits, flux qubits and phase qubits that mentioned above are perfectly compatible with the current microelectronic processing technology. Although the current in the wires and the charge on the capacitors in a quantum circuit is in a superposition state compared with the traditional circuit, these wires and capacitors can still be made from current microelectronic processing technology without the need to invent now capacitors and wires. This means it is convenient to extend superconducting system. The good scalability makes the superconducting quantum computer have a high priority, because the fault-tolerant quantum computing which can reduce the error from the decoherence time and the experimental operation need a large scale of qubits. Thus the quantum error correction is the key to make the result of quantum computer credible.

3.2.Disadvantages: The main problem of quantum computer is that it is hard to improve the coherence time of quantum system. As quantum state is very feasible, it is easy to be influenced by the environment. Coherence makes quantum computer superior to traditional computer, although there are some methods such as cavity quantum electrodynamics theory that are introduced into the superconducting system to solve the decoherence time problem. In addition, as mentioned above, the problem decoherence time has not been completely solved. And other important problems of the superconducting system come from Josephson junction. For instance, it is very difficult to reach the absolute zero, so the Josephson junction can not be a non-dissipative component. And it will influence the stability of quantum computer. Therefore, there are many problems need to be solved to realize superconducting quantum computer.



If you interest in Rydberg qubits, knowing about their progress and challenges, this paper will be good:

Quantum computing with atomic qubits andRydberg interactions: Progress and challenges

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