The "Philosophical debate to quantum technological revolution" pipeline

The “Philosophical debate to quantum technological revolution” pipeline

Introduction

What is real? And why does Quantum Mechanics - one of the most accurate physical theories - sometimes only offer probabilistic results at best? Questions like these brought forth the quantum technological breakthrough. It is a great example of how asking the right questions and addressing the elephant in the room led to real progress. From the very abstract to the very real.

At the beginning of the previous century, it became clear that quantum mechanics could explain experimental data with remarkable accuracy. Great scientists of the period contemplated the meaning of this in relation to our understanding of the world. Figuring out what quantum theory meant was more important than ever, because Quantum theory contrasted common logic and day-to-day experience like no other.

EPR’s objection to Quantum Theory

One of the firmest critics of Quantum theory was Einstein, whose theory of relativity was still new at the time. At first, it really seems like these two theories contradict each other. Relativity allows only local interactions, and quantum mechanics (QM) seems to allow extremely non-local phenomena.

But what is considered “local” in physics? Simply put, local interactions happen from one point to the other, meaning that if two systems interact from a distance, the space between them is affected too. Conversely, a non-local interaction would be an event in point (A) affecting point (B), which can be as far as it may, without affecting the intermediate space.

Quantum mechanics is imbued in non-local interactions, and for Einstein, that was its main weak point. In fact, he, along with Podolsky and Rosen, published the infamous EPR paper in 1935, which made the extreme non-locality of QM crystal clear. For them, that, along with a couple more arguments about the nature of probabilities in QM, conflicted with their definition of reality itself… Indeed, that paper starts by defining what is to be considered real.

Of course, the experimental data aligned with the QM results, so EPR did not argue that QM is wrong, but…incomplete. They believed that a wavefunction does not provide a full description of a system (which is what QM argues), but an alternative theory that does provide the full picture is possible. Their argument was later refined and passionately supported by Bohm, who proposed a hidden variable theory.

On a side note, a lot more happened in between, as with any major advancement in science, but a complete historical analysis is beyond the scope of this blog. Key events are:

• Einstein tried making his own hidden variable theory, but withdrew his paper before publishing, probably because he realized that his version also allowed non-local phenomena, in contrast to what he wanted to achieve.

• De Broglie comes up with the infamous pilot wave interpretation of QM, which is also a hidden variable theory, but after receiving criticism at the Congress, and especially by Pauli, he abandoned his theory..

• Bohm’s hidden variable theory accidentally came to the same result (and went beyond) De Broglie’s pilot-wave theory, and thus this alternative interpretation of QM is called De Broglie-Bohm.

Bell saves the day

The response to the issues raised by EPR came from John Bell in 1964, where he proved that local hidden variable theories cannot reproduce the results of quantum mechanics. That paper shaped the understanding of quantum mechanics for many reasons:

• The proof of the main point is general: it applies to all hidden-variable theories that try to equip quantum mechanics with locality. It could be argued that Bell did not prove the misalignment of QM and hidden variable theories, but QM and locality itself. (which is a little ironic given that EPR’s problem with QM is the lack of locality)
• It allowed for an experimental verification of the very nature of probabilities of quantum mechanics (experimental data confirmed Bell’s theorem and the relative work was awarded by the Physics Nobel prize of 2022 (RIP Bell, you would have loved your Nobel prize award…on a second thought, it makes sense since it is called the no-bel prize…okay I shut up))
• It shut down once and for all the argument that, since QM is non-local, it cannot be complete.
• It put the notion of entanglement in the spotlight.

The last characteristic of Bell’s paper is one no one saw coming. At that point, entanglement was a known part of the Quantum theory, but its significance wasn’t fully understood yet.

The birth of Quantum Information Science and Applications

Entanglement, along with superposition, allowed for new ways of analyzing, harnessing, and transmitting information and gave birth to a new field of science called Quantum Information Science. Quantum algorithms were invented by theoretical research in this field, which promise computational advantage over classical computation, which is to be realized once the quantum hardware infrastructure gets up to speed.

The most promising applications of these quantum algorithms are:

• Fast and accurate simulations of complex quantum systems, which would revolutionize all of material science (from pharmaceutical discoveries to finding room-temperature superconductors to unlocking the mysteries of bacteria to achieve eco-friendly fertilizer production, etc.)
• Surpassing classical computation in optimization problems and stochastic processes with applications in financial modelling, machine learning, weather forecasting, climate change, and many more.
• Breaking current cryptography by extremely efficient integer factorization, a threat so real that measures for quantum-safe cryptography methods have already been discovered and are being implemented slowly.

Conclusion

Achieving quantum advantage would change the trajectory of human history. And if the applications of quantum algorithms sound truly insane … that’s because they are. From the very beginning, quantum mechanics hasn’t stopped being mind-bending. It all started with asking:

What is real?

“If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.” - Niels Bohr