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Published 14 June 2024 by Andrei Mihai

Unlocking the Quantum World: Theory, Technolgy, and Hype

Inside the Quantum Lab. Photo/Credit: John D/iStockphoto

Quantum Physics and Quantum Technologies are among the key themes of this year’s 73rd Lindau Nobel Laureate Meeting. A discussion of the status quo, including prospects and questions to be discussed as part of the programme.

Quantum mechanics, the science of the very small, has been both exciting and contentious ever since its inception. Unlike classical physics, which deals with predictable and intuitive phenomena, quantum mechanics is notorious for its counterintuitive principles. For instance, particles can exist in multiple states simultaneously, a phenomenon known as superposition; they can also become entangled, meaning the state of one particle instantly influences another, no matter the distance separating them.

Although some of its core phenomena have been robustly proven, reconciling quantum mechanics with general relativity has proven immensely difficult. This has big implications for our understanding of the universe and suggests something may be missing from this understanding – but let us leave the abstract universe aside for a bit. Quantum physics has also inspired several promising technologies with a much more tangible side.

Some of this progress comes from the work of 2022 Nobel Laureates in Physics: Alain Aspect, John F. Clauser and Anton Zeilinger. The three Laureates conducted experiments using the key quantum property of entanglement, in which what happens to one particle affects another, even if they are separated by a distance. “The ineffable effects of quantum mechanics are starting to find applications,” noted the Nobel Prize announcement – and indeed, they are.

Quantum Sensors and Medicine

The word “quantum” has become used in many different contexts. In some instances, it is a hype word, but the quantum world also carries definite potential for real-world technologies (as discussed in Tuesday’s panel at #LINO24). Literally, the term “quantum” originates from the Latin word for “how much”. It refers to the smallest possible discrete unit of any physical property, such as energy or matter (called a quanta).

In real-life technologies, “quantum” refers to the application of principles from quantum mechanics to create innovative devices and systems. For example, quantum computing leverages quantum bits (qubits) that can exist in multiple states simultaneously, vastly increasing computing power and solving complex problems faster than traditional computers. Quantum cryptography utilizes quantum principles to develop secure communication methods, ensuring that any attempt at eavesdropping can be detected. Additionally, quantum sensors and imaging technologies enhance precision in measurements and medical imaging, leading to advancements in fields like healthcare, navigation, and environmental monitoring.

Some technologies that use quantum effects have been around for some time.

Take Magnetic Resonance Imaging (MRI) technology, for instance. MRIs utilize quantum effects primarily through the principles of nuclear magnetic resonance (NMR). In MRI, powerful magnetic fields and radiofrequency waves are applied to the human body. Hydrogen nuclei, which are abundant in the body’s water and fat molecules, have a quantum property called “spin” that makes them behave like tiny magnets. When placed in a strong magnetic field, these spins align with the field. Radiofrequency pulses then knock the spins out of alignment, and as they return to their original state, they emit signals. These emitted signals are detected and translated into detailed images of the body’s internal structures. The quantum behaviour of nuclear spins, such as their quantized energy levels and interactions with magnetic fields, is fundamental to the operation of MRI, allowing for non-invasive and highly precise medical imaging.

Quantum dot is a semiconductor crystal of nanometre dimensions with distinctive conductive properties determined by its size.
Colloidal quantum dots irradiated with a UV light. Differently sized quantum dots emit different colors of light due to quantum confinement. Photo/Credit: Tayfun Ruzgar/iStockphoto

Other medical sensors also use quantum effects and practices used in biological research proceed in the same way, so if we are looking for established quantum technology, the medical field is actually a good place to start.

But other fields have produced less tangible results.

Quantum Cryptography

Perhaps the most tantalizing quantum technology is quantum cryptography.

Our entire society relies on secure communication, but it is becoming increasingly difficult to keep communication systems secure. This is where quantum mechanics could make a world of a difference, offering unparalleled security for communications. If the process of key exchange (the core of cryptography) uses quantum states, these states cannot be copied or measured without altering their state and alerting the parties involved. This leverages one of the fundamental properties of the quantum world, and it means that eavesdropping on communications can be immediately detected. This can be further enhanced by quantum entanglement which could create encryption keys that are theoretically unbreakable.

Despite this promise, however, implementing quantum cryptography poses major technical challenges.

For starters, it requires advanced technology, such as single-photon sources and detectors, which are still in the experimental stage and can be difficult to integrate into existing communication infrastructures. Quantum signals are highly susceptible to loss and noise over long distances. Current quantum cryptography systems struggle with maintaining signal integrity over more than a few hundred kilometers without the aid of quantum repeaters, which are still under development.

The cost, scalability and sensitivity to environmental impact are all problems that need to be overcome. Investments are coming in to address these issues; in one project alone, the EU investing € 18 billion, and several national and international projects are on the billion-dollar scale. Despite all this progress, however, scalable quantum cryptography is still not in sight, though big breakthroughs seem to be right around the corner.

Then, of course, there are computers.

Quantum Computers

Quantum computers use the principles of quantum mechanics to process information in fundamentally different ways compared to classical computers. They utilize quantum bits, or qubits, instead of the classical bits.

A futuristic glowing quantum computer unit, 3d render
Model of a quantum computer. Photo/Credit: bpawesome/iStockphoto

These qubits can exist in multiple states simultaneously (superposition) and can be entangled with each other, allowing quantum computers to perform some types of complex calculations at unprecedented speeds.

This capability makes quantum computers particularly important for solving problems that are currently intractable for classical computers, such as factoring large numbers, optimizing complex systems, and simulating molecular and quantum interactions for drug discovery and materials science. Some quantum computers have already been developed, though we have not yet reached the full potential of a mature quantum computer.

For now, classical computers still outperform quantum computers for all real-world applications, and serious hardware problems remain (particularly for scaling quantum architecture). Nevertheless, this is another field in which quantum technologies promise to be revolutionary, even though not quite yet.

Quantum Technologies Are Opening Up

There are several other quantum technologies currently being developed. Take quantum radars, for instance, which use entangled microwaves to detect low-reflectivity objects at room temperature. Such radars may not only be used in conventional radar applications, but also as medical imaging systems. Quantum sensors with applications from GPS to brain scanners are also being developed, often with tangible progress.

We may not understand all the quantum secrets of the universe, but thanks to the work of pioneers like Aspect, Clauser, and Zeilinger, and to the many researchers and engineers building on their work, we have access to an array of new technologies – and we are still only scratching the surface of what the quantum world has to offer.

Quantum mechanics has given us a lot, both in terms of our understanding of the universe and in terms of the innovative technologies it inspires.

In 1918, the Nobel Prize in Physics was awarded to Max Planck, for his “discovery of energy quanta.” Less than two decades later, in 1932, Werner Heisenberg received the same honour for “creating quantum mechanics.” Several other Nobel Prizes in Physics have been awarded the prize for contributions to the quantum world, including Max Born and Richard Feynman, as well as Tuesday’s panelist Serge Haroche and the 2022 Laureates, Aspect, Clauser and Zeilinger.

Undoubtedly, the quantum world has given us a lot – and we are still only scratching the surface. While “quantum” may sometimes be overused as a buzzword and the journey to fully integrate these quantum technologies is still ongoing, the promise for tangible technologies is undeniable.

Andrei Mihai

Andrei is a science communicator and a PhD candidate in geophysics. He co-founded ZME Science, where he tries to make science accessible and interesting to everyone and has written over 2.000 pieces on various topics – though he generally prefers writing about physics and the environment. Andrei tries to blend two of the things he loves (science and good stories) to make the world a better place – one article at a time.

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