My first encounter with quantum physics was in a college survey course many years ago. The course took a historical approach, exploring groundbreaking experiments that introduced concepts of uncertainty, quantization, and probability. Einstein’s challenging Gedankenexperimente—thought experiments that continue to provoke our interpretations of physical reality—dominated our discussions. While these concepts seemed abstract and lacking immediate practical value, they highlighted the profound departure of quantum mechanics from classical thinking.
As part of my studies for my first physics degree at Grenoble, I mastered the Dirac notation—also known as bra-ket notation—well enough to apply it to simple experiments in optical spectroscopy. This experience clearly demonstrated the power of mathematical methods that sidestep philosophical questions to generate accurate results using elegant linear equations. I then used these techniques for my graduate research on quasi-molecules formed during noble-gas atom collisions.
After my PhD, my career took a different direction, and I focused on inventing and developing optical instruments to measure distances and surface shapes with high precision. As years turned into decades, I found myself far removed from the world of quantum physics, no longer calculating expectation values with Pauli matrices or debating the fate of Schrödinger’s cat.
Then last year, while heading down the escalators at the Moscone Center for the SPIE Photonics West trade show, I decided to turn left instead of going straight, and paid a visit to Quantum West. And there they were, my old quantum mechanical friends, Bra and Ket. What they were up to after many years of being out of touch astonished me.
Today, what were once fanciful thought experiments are being applied in groundbreaking quantum technologies. Blackboard puzzles like the Elitzur-Vaidman “undetected photon” paradox have become the foundations for ghost-imaging techniques and quantum encryption. Perhaps the most dramatic advance has been the rise of quantum computing. The idea that we can manipulate optical and semiconductor qubits, modify their wavefunctions, and entangle them to perform probabilistic calculations seems far-fetched, until you see it done.
“Seeing it done” in quantum experiments would seem out of reach for most of us, given the need for exotic hardware and liquid helium supercooling. Thanks to cloud-based computing and accessible software development kits, today, anyone can program quantum computers. Just for fun, I can now design circuit models of single-photon interferometry experiments and run them on real quantum computers, remotely, from my desktop. Optics and photonics play essential roles in this modern-day magic, from the fiber cables that connect us to the internet, to the laser traps that arrange neutral-atom qubit arrays, and the photons that tease out the answers to questions we didn’t even think to ask.
As I wander the Quantum West trade show floor this year, I reflect on how far SPIE has come. Founded in 1955 to support engineers in the niche field of photographic instrumentation, SPIE now serves industries as diverse as biomedical instrumentation and commercial sensing. In 2025, seventy years after its founding, SPIE is one of the partners administering the first International Year of Quantum Science and Technology (IYQ). In June, SPIE will once again host the Photonics for Quantum conference in Waterloo, Canada.
My recent rediscovery of quantum mechanics proves to me once again that it pays to explore outside of one’s specialization at SPIE conferences to gain inspiration from the ever-expanding boundaries of optics and photonics.
Peter de Groot
2025 SPIE President
