Quantum Programming and Quantum programming languages: the myth, reality, and possibilities (Cont'd).
Felix Wejeyan
Theoretical & Mathematical Physicist PhD Researcher | Quantum Computation Researcher.
If you missed the first part of this newsletter, please read for continuity: https://www.dhirubhai.net/pulse/quantum-programming-languages-myth-reality-felix-wejeyan-s3c7c
One important question at this point is: what is an idealistic quantum program? An ideal quantum program are combinations or sets of instruction in a quantum programming language designed for a quantum computer to execute. The next puzzle from this definition is, what is a quantum programming language? An ideal quantum programming language is composed of syntaxes and semantics usually defined by the laws of quantum mechanics or even worst, quantum mechanical probability amplitude. What are quantum syntaxes? Quantum semantics? Quantum mechanical probability amplitude? If you feel like your head is spinning, it is because just like you, we all are trying to bite our tail; the theory isn’t complete.
If there is one thing the theoretician has been able to establish with all forms of quantum programming language is the fact that whatever might be going on in the “head” of any quantum computer is highly probabilistic and completely unknown to us. This is because of the limitations of the way we “know”. All we can do, and all that we try to do, is to try to control and define the prevailing conditions of operations of the quantum computer, and leave the computing beast to use these prevailing conditions to do whatever it thinks is best and how it thinks is best based on the specific algorithm we are able to translate to it to implement and based on what we know about an isolated quantum system in the established condition. This is unlike our classical computer, which we actually do “know” what is going on in its head and are able to control how it thinks through a processor. A smart idea would be, let us create a quantum processor, right? This should solve the problem.
Please be patient, let us try to bite our tail one more time. What is a quantum processor? The ideal quantum processor is the brain or “head” of the quantum computer that controls how it solves quantum algorithmic problems. Wait a minute! I thought we just agreed that we do not know and cannot control whatever might be going on in the head of a quantum computer? Confused? Do not worry, we all are, every one of us. There are lots of tech companies clamoring and fighting to design a quantum processing unit (QPU), and they all agree about one thing; the currently designed quantum processing unit doesn’t actually control anything. As a matter of fact, they actually have to be controlled themselves. Moreover, we are still trying to design a quantum algorithmic problem that we can feed into a quantum computer for it to solve.
Let us try to put all of our confusions into one basket: maybe this would help. The theoreticians has tried to explain timelessly that we do not have a proper understanding about many phenomenon we have slammed with the word “quantum”. We are still trying to understand the syntaxes and semantics that we can use to properly translate the laws of quantum mechanics and probability amplitude into executable commands and algorithmic problems for a quantum computer to process and solve. While at the same time, we do not know how a quantum computer processes its algorithms. Some say it is through the manipulation of the quantum bit (qubit), but that is another confusion of its own.
What then are pseudo-quantum programs and programming languages? And, what then do we actually know about quantum computation? Shor’s algorithm has proven unequivocally that a digital computing device cannot simulate a quantum probabilistic event. Factoring integers and finding discrete logarithms are two problems that are generally considered to be difficult for classical computers: this knowledge has been used for encryption technologies in the global digital security systems. Shor’s algorithm hypothetically redefines what the mathematical implication of a computing device should be from the classical Church-Turing thesis into an extended version that a Turing machine is unable to simulate: thus, this extends the meaning of “compute” for any mechanical computing device. In other words, if all classical computing devices are limited by the Church-Turing thesis, then a quantum computing device can simulate problems that a classical computer can, and as well those that it cannot. This is regarded as quantum supremacy.
Quantum supremacy is still at its infancy stage, and every quantum programming languages out there is only trying to use Shor’s algorithm to extend their meaning of computation into a dimension where they can understand and control what computation means for a quantum computer, and translate this meaning into a classically digitized signal. The signals they are getting from these quantum computers based on all current approach to the problem are filled with random and probabilistic data they regard as noise or errors, so they believe they would need a quantum error correction system. A quantum error correction system is a problem for another day.
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A purely quantum computational device cannot be understood or simulated by a classical computational device at all times, but we are hoping that it can be somehow controlled by it. This is the logical foundations that makes every current quantum programming language pseudo-quantum. We can delve further and deeper into its implications by looking at the structure of quantum logic circuits and gates, the Toffoli gate for instance; but we would find ourselves still trying to bite our tails again.
All current quantum programming software and programming languages uses a classical approach to solve Shor’s algorithm, and are thus classically bounded. This is why there have been many papers published that imply that all current quantum computers can be simulated by a Turing machine, and are thus bounded by classical computation. A pure quantum programming language has no classical equivalence, but in itself encompasses and supersedes the computational abilities of all classical Church-Turing computational devices. The biggest problem with quantum computation is finding a syntax and a quantum semantic structure to form questions and solutions of problems like Shor’s algorithms. And this further boils down to our ability to create an ideal quantum processor, and eventually an ideal quantum computer. ?
We’ve always thought of computers and its accruing computational capabilities and software as tools with which to explore deeper into the unknown and bizarre aspects of our reality, but with quantum computers, we are in for a great surprise. We should come to the acceptance that when quantum supremacy is achieved, it would be something that we had never anticipated. It would not conform to our needs, or answer questions that we have considered for a long time as important or imperative to the advancement of our science or existence; rather it will be uncompromising and have a “will” of its own. The only thing we are somewhat certain about and can maybe control is our ability to define its outlining and existing parameters, and thus confining its sample and integrating space within predefined predictable dimensions.
In order to achieve this control, we would need a means of communicating with these quantum computers in a pure quantum programming language; and a sophisticated means at that. It is this control we hope to have that we would be able to digitize, manipulate and program into a software so that the quantum computer would be able to limit its computational potentials to the set of algorithms we want to implement, thus minimizing the noise and errors received and translated from quantum computational results of the quantum computer. To be able to define a precise computational tactics with which to predict and control how a quantum computer should and would carry out its computation is still by all means beyond our theoretical capabilities. As soon as they are within our capability, a whole new world of computational possibilities would be opened for us to explore.
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Next week’s publication: PHENOMENOLOGY: THE PHYSICIST’S “SUPERPOWER” OVER THE MATHEMATICIAN IN THE BATTLE FOR OUR UNDERSTANDING OF QUANTUM FIELD THEORIES.
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