It was late 2019 when Google first claimed having achieved “supremacy” in quantum computing. The controversial claim was politely questioned by some scientists, publicly scorned by others, and downright ridiculed by its archrival, IBM. According big blue, the problem posed for the experiment by Google’s quantum computer, named Sycamore, was comparatively simple and could have been solved with a classical digital computer, although it must be recognized that in a much longer period. In fact, as things stand, any computational problem can be solved with a classical computer if given enough time to complete the task, but that could take thousands of years and would therefore be inherently useless.

And that’s the problem: in any computational problem in quantum computing, “quantum supremacy” – a term first coined in 2012 and which several companies have boasted about at every opportunity since – refers to the repeatable demonstration of the solution. using a programmable quantum device. to a problem that no classical computer, of any size, could solve in a practically feasible period of time. In other words, finding a verifiably correct answer in less than ‘n’ period, where ‘n’ can be anything between one human generation or less, or tens of millennia or more.

Critics say that the very term “quantum supremacy” infers a state of complete ascendancy of the technology and its ability to solve a specific, but not necessarily relevant or significant, problem faster than a classical computer and is therefore too enthusiastic and triumphalist. Another, less pejorative, term is “quantum advantage,” which is considerably more subtle than the notion of “supremacy,” because it implies that a quantum computer can solve a real-world problem better than any binary-based classical computer.

TelecomTV has been talking about quantum supremacy and other quantum computing issues with author and scientist Lawrence Gasman, former senior telecommunications researcher at the Washington DC-based think tank the Cato Institute, and the founder and president of the house research and consulting firm Inside Quantum. Technology.

He is a man who knows his quantum problems (so to speak) and who maintains that quantum supremacy “is a very unpleasant term… quantum advantage is less aggressive.” And so it is, but that has not prevented Google from returning four years later to claim, for the second time, that it has achieved this through the latest version of its Sycamore quantum processor, which works at 70 qubits instead of 53 qubits. of the machine used in the 2019 test.

As the addition of new qubits, the building blocks of quantum computers, exponentially increases the powers of quantum devices, the latest version of Sycamore is 241 times more powerful than 2019’s Sycamore. This, Google says, puts it “ beyond the capabilities of existing classical supercomputers.”

The Google paper “Phase Transition in Random Circuit Sampling”, which is published on the open access scientific website ArXivclaims that Hewlett Packard’s Frontier supercomputer would take 47.2 years to perform the same calculation and produce the same result that the new Sycamore achieved virtually instantaneously.

Even though Google’s latest test served no purpose other than to serve as a demonstration to support a claim of quantum supremacy, and did nothing of practical use or apply the kind of high-level bug fixes that will be vital to allowing Quantum computers provide answers to significant real-world problems, as an exercise it is flashily impressive in the same way as a fireworks display: entertaining but expensive and achieving little lasting value or significance.

Or, as Gasman puts it, “quantum supremacy could mean that we’ve built a problem that no one gives a damn about, but we can show that the problem can’t be solved in a reasonable amount of time with a classical computer, but it can be solved. with a quantum computer, and that proves something.”

He added: “Researchers view quantum supremacy primarily as a scientific goal, with relatively little immediate influence on the future commercial viability of quantum computing. Due to potentially unpredictable improvements in classical computers and algorithms, quantum ‘supremacy’ may be temporary or unstable, placing potential achievements under significant scrutiny.”

racehorses

Current quantum computers are “noisy”, error-prone and fault-intolerant and it is clear that the future of computing will not be a one-horse race but a matter of “horses for races”. Quantum machines will be of immense importance and value, but they cannot and will not do everything. The power and speed of classic computers continue to increase and each time a new record is achieved for one of them it is quickly surpassed by another.

Thus, for eight months last year, between March and November 2022, Hewlett Packard Enterprise’s (HPE) “Frontier” exascale supercomputer was the fastest in the world. Then, in November, it was surpassed by the “Flatiron” supercomputer, which is owned by the Simons Foundation’s internal research division and serves five computational science centers. You can bet it won’t be the world’s fastest classical computer for long either.

What is certain is that for many computing applications, the classical computer will not only continue to coexist with quantum computing but will also dominate it in many application areas. Quantum computing, due to its dependence on quantum physics concepts and other technological limitations, will for the foreseeable future be mainly limited to certain application areas such as artificial intelligence (AI), chemical engineering, cryptography, finance, logistics and the materials. science, climate systems modeling, pharmaceutical research and drug discovery, as well as subatomic physics and simulation of quantum and other systems and problems.

This is because quantum computers are excellent at solving complex problems through statistical approximation and optimization. The structure and properties of qubits allow them to manage such processes much faster and more efficiently than classical computers, and that is because they process data in a fundamentally different way than binary computers.

In classical computing, a “bit” comprises the set values of a “zero” or a “one”, but in quantum computing the quantum property of superposition is simultaneously exploited to store data in qubits with an indeterminate value which can be a zero or any combination of the two. The ability to hold two bits of information at the same time means that a quantum computer can work on multiple problems simultaneously. It is also a property that allows large amounts of data to be stored in a much smaller space than is possible for a classical binary computer, and to store it in a much shorter time.

What is needed is to move to what is called “utility quantum computing,” where devices with thousands of qubits will provide solutions to some pressing real-world problems at a speed much faster than any classical computer could achieve. However, that will depend on quantum machines being built with enough redundancy to allow an increasing number of qubits to work together instantaneously to correct the propagation of errors that currently and inherently inhibit the devices from working long enough to solve real problems. world problems before breaking down and stopping the execution of a program.

Quantum computers are extremely sensitive to noise and errors caused by interactions with their environment, and it could be something as simple as a stray ray of light. As a program progresses, errors accumulate and degrade the calculation. Quantum systems do not lend themselves well to being in a defined state, even for a very short period of time, and therefore a quantum system will very quickly drift out of phase, decohere, become entangled, and collapse.

Most quantum scientists consider error correction as the central problem that must be solved before practically useful quantum computers can be built and operated.

In the second part of this report, TelecomTV will cover the main challenges currently facing quantum computing and some of the proposed solutions to them, and will analyze what Gasman considers to be the imminent threat to public key encryption (PKE), cryptography asymmetric that has, so far, kept systems and networks (including the world’s telecommunications networks) secure for a generation, but perhaps not for much longer.

And finally, a short quantum joke: Schrodinger goes for a Sunday walk along a country road. The car raises a cloud of dust and provokes the suspicions of a traffic police officer. He stops Schrodinger, looks at his driver’s license and insurance details, and then asks for the trunk to be opened. Schrodinger pulls the trigger, the cop looks inside, then walks around the car and says, “Sir, do you know you have a dead cat in the trunk?” Schrodinger replies, “Well, I wasn’t, but now I am.”

*– Martyn Warwick, Editor-in-Chief, TelecomTV*