This informal paper documents my thoughts in recent months on IBM’s quantum hardware roadmap which they published on September 15, 2020, as well as their quantum software development and ecosystem roadmap published on February 4, 2021. This paper focuses primarily on the former — the hardware — more than the latter, although a future paper may delve into the latter and there is a section on the latter at the end of this paper.

Overall, we can all be grateful that IBM is giving us a view into their future, unfortunately it raises more questions than it answers. The roadmap…


The great promise of quantum computing is that an application running on a quantum computer should have a truly dramatic and compelling performance advantage over a comparable application running on a classical computer, not merely a minor to moderate performance advantage, but what defines dramatic? The ideal for quantum advantage is a so-called exponential speedup. This informal paper explores and sets out a model for judging how dramatic an advantage a quantum solution has over a classical solution.

There is no standard definition for what constitutes either quantum advantage or dramatic quantum advantage or how they should be measured, but…


For convenient reference, this informal paper presents the timeline of the notable computers during the early history of classical computing in the 20th century. I compiled this timeline due to my interest in the rapidly developing field of quantum computing, to assess what parallels might exist, now and in the future — after all, we’re supposed to learn lessons from history, lest we be doomed to repeat the mistakes of the past.

There is also a section at the end summarizing some of the early application milestones for early classical computers.

What’s not included

This timeline excludes most precursors to modern computing, including…


Qubit fidelity is an urgent matter for quantum computing. Even with a large enough number of qubits, the fidelity of the qubits is a key gating factor in how useful a quantum computer can be. This informal paper will discuss the terminology used to discuss qubit fidelity as well as the many issues which arise around qubit fidelity. Nines are a shorthand and simply defer to orders of magnitude, powers of ten. Actually, nines are the order of magnitude of the inverse of the error rate. …


We need decent terminology and scales of distance when discussing the interconnection of quantum computing elements, whether they be individual qubits, lattices of qubits, chips of qubits, modules of qubits, subsystems of quantum computers, complete quantum computers, or networked quantum computer systems, from 1 angstrom to millions of miles. This informal paper scopes out the magnitude of the distance scales for interconnecting quantum computing elements. These concepts also apply to quantum sensing, and quantum storage.

The goal here is that when someone speaks about quantum connections, modular quantum computers, quantum networking, and distributed quantum processing, we need to understand what…


NISQ has been a great way to make a lot of rapid progress in quantum computing, but its limitations, particularly its noisiness and lack of robust, automatic, and transparent error correction, preclude it from being a viable path to true, dramatic, and compelling quantum advantage for compute-intensive applications which can be developed by non-elite developers which would simply not be feasible using classical computing. Absent perfect qubits, automatic and transparent quantum error correction (QEC) is needed to achieve fault-tolerant qubitslogical qubits — to support fault-tolerant quantum computing (FTQC.) …


Living in Washington, DC, it was easy for me to swing over to the U.S. Capitol to attend President Trump’s first impeachment trial in the Senate back in 2020. Now that Trump is on trial for impeachment again, I figured that my experiences might be of interest. This informal paper is a compilation of my contemporaneous Facebook posts from late January and early February of 2020.

  • For the most part, my writing here is strictly apolitical, merely describing my experiences and direct observations, with no partisan political interpretation. The only possible exception is the postscript sections with my views on…

Here are my top wishes for developments in quantum computing for Christmas in 2020. Okay, that’s too tall an order with too little time left, so this informal paper lists the quantum computing developments I really want to see in the coming year, 2021. It’s a fun list, but it’s also a real list — these are advances that have a realistic chance of occurring over the coming year.

For reference, here’s my Christmas wish list from last year:

I still want everything from my 2019 wish list…


Phase is central to quantum computing, but there is a risk that algorithm designers may lean too heavily on fine granularity or gradations of phase, seeking a precision that just isn’t there in the theory or actual physics or engineering of real qubits. This informal paper will explore the phase property of qubits, with an eye on the limits of precision or granularity of phase.

Unfortunately, this paper may provide much more in the way of questions than in actionable answers, but coming up with deep and clear questions is the first step to getting answers that are both meaningful…


The IBM paper which introduced the notion of quantum volume as a metric for the power of a quantum computer has the odd caveat that it applies only to quantum computers of “modest size”, up to approximately 50 qubits. Why this odd limitation? Simple: because IBM’s method requires classical simulation of randomly-generated quantum circuits, which is exponential in the number of qubits, so 2⁵⁰, which is roughly one quadrillion (1,000,000,000,000,000 — a million billion) is considered the limit of the number of quantum states which can be represented and simulated on a current classical computer. …

Jack Krupansky

Freelance Consultant

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