Celebrating the First Century of Quantum Physics and Preparing for the Next One

A century ago, pioneering scientists, including Wolfgang Pauli, Werner Heisenberg, and Erwin Schrödinger, laid the foundational principles of quantum mechanics. To mark this milestone, the Editors of the Physical Review journals have curated a collection of landmark papers that shaped the field. The whole collection is accessible at this link.

The collection begins with the following editorial by Dagmar Bruß from Heinrich Heine University Düsseldorf.

Physical Review Letters’ Editorial

In this International Year of Quantum Science and Technology, we celebrate the centenary of quantum physics. The anniversary marks the theoretical developments—including Heisenberg’s and Schrödinger’s formulations of quantum mechanics—that swiftly unfolded starting in 1925, building on earlier seminal contributions that established essential quantum concepts [1–5].

One hundred years span about three human generations. Similarly, I view the last century of quantum physics as progressing through three consecutive but intertwined generations. The first quantum generation was an era of understanding and mysteries. The groundbreaking works of this period introduced a formal quantum-mechanical description of physical reality. At the same time, this era saw researchers trying to cope with the counterintuitive phenomena—including entanglement and the related nonlocality—resulting from the quantum formalism.

The second quantum generation was one of consolidation and applications. This era brought about the “first quantum revolution”—a series of technological breakthroughs that have made quantum effects a part of our daily lives. Lasers, magnetic resonance imaging, and integrated circuits are all examples of quantum-enabled technologies. Quantum theory also started to reshape fields such as chemistry, materials science, astrophysics, and cosmology. This period came with a gradual acceptance of the peculiar effects emerging in the quantum regime.

The characteristic feature of the third quantum generation is the link with information science. Having come to terms with quantum weirdness, scientists realized that the quantum world has great, inherent power for quantum information processing. Harnessing the quantum laws of nature, they devised ways to perform computing, communication, simulation, and sensing with unmatched efficiency and security. Efforts to implement these disruptive technologies lie at the heart of contemporary research.

This collection brings together papers playing a foundational role within each of these three quantum generations. In the first generation, the development of the theory [6–17] went hand in hand with the discussion of doubts, paradoxes, and possible interpretations of quantum mechanics [18–22].

During the second quantum generation, pioneering contributions included insights into topological effects [23,24], as well as the conception of experiments for proving debated quantum-mechanical properties such as nonlocality [25–27], contextuality [28], and particle-wave duality [29]. These ideas were successfully tested in experiments when suitable technology became available [30–34].

The third quantum generation was opened up by papers that built the foundations of quantum information science. The “no-cloning theorem” [35] showed the possibility of achieving unbreakable security in quantum communication [36]. Other landmark papers pointed out the possibility of building a universal quantum computer [37] and of achieving a quantum computing advantage in practical applications [38]. In parallel to quantum information science, foundational research started to pursue new and alternative directions [39].

As we enter a new century of quantum science, we wonder how disruptive quantum information technologies will be, and on what timescales their full impact will be felt. But future quantum research will need to tackle much more than technology development. After 100 years of quantum mechanics, several fundamental issues remain partially or fully unresolved. Can we understand the boundary between the quantum and the classical world? How can the laws of classical thermodynamics emerge from quantum mechanics? Can gravity be quantized, and how can experiments look for signatures of quantum gravity? Many more questions will arise that we cannot even imagine today.

Certainly, research on foundational aspects of quantum physics will be as necessary in the future as it was in its first century. And as history has amply shown, so-called “quantum leaps” in technology are by and large the fruit of fundamental advances.

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Featured image: Max Planck and Albert Einstein (Hebrew University of Jerusalem).