Despite the dramatic advances of quantum computing in recent years, I find it odd that there are no 40-qubit quantum algorithms or even 32-qubit quantum algorithms, even though there are several real quantum computers with more than 50 qubits and we have 40-qubit simulators. This informal paper will explore the merits and issues related to 40-qubit quantum algorithms.

Current classical quantum simulators are capable of simulating 40 qubits, but how come we are not seeing published algorithms exploiting 40 or even 32 qubits?

Toy algorithms (fewer than 24 qubits) are great to prove that basic hardware features of a quantum…


How can the designer of a quantum algorithm know that the algorithm will work for far more qubits than it has been tested or far more qubits than can be simulated (50 qubits max)? This informal paper proposes a model for design and testing of scalable quantum algorithms.

The ambitious goal of quantum computing is dramatic quantum advantage, where a quantum algorithm can outperform a comparable classical algorithm by a truly amazing factor. Not just a factor of 2X, 10X, 100X, 1,000X, or even 1,000,000X, but far more than even a factor of a billion or a trillion times the…


There is more than one reason to simulate execution of a quantum circuit on a classical computer. This informal paper proposes a model of five distinct major use cases and a variety of access patterns for a classical quantum simulator. The goal is to complement real quantum computers to enable a much more productive path to effective quantum computing.

First, here’s a brief summary of the kinds of use cases and access patterns for simulation of quantum circuits on classical computers:

  1. Simulate simply because a real quantum computer is not yet available. Or that available real quantum computers are insufficient…

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…

Jack Krupansky

Freelance Consultant

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