Quantum Technologies II: Electron Microscopes, Quantum Computing and Society

Seeing smaller than light allows

In The Wave Nature of Light you saw that diffraction blurs images: a microscope cannot show details much smaller than about half the wavelength of the light it uses. With visible light (400 nm to 700 nm), the best optical microscopes resolve about 200 nm. That is enough for cells and bacteria, but most viruses (about 20 nm to 300 nm) are a blur or invisible, and individual molecules are hopeless.

de Broglie's equation offers a way out. Electrons accelerated through tens of thousands of volts have wavelengths of a few picometres, about 100 000 times shorter than visible light. Use electrons instead of light, and magnetic coils as lenses (moving charges are deflected by magnetic fields, as you learned in Gravitational, Electric and Magnetic Fields), and you can image far finer detail.

Electron microscopes: TEM and SEM

• A transmission electron microscope (TEM) sends a beam of electrons through a very thin slice of the sample. Magnetic lenses focus the transmitted electrons onto a detector. TEMs show internal structure: cell organelles, crystal defects, the arrangement of atoms in a material.
• A scanning electron microscope (SEM) scans a fine electron beam across a sample's surface. Electrons knocked out of the surface are counted to build a striking, three-dimensional-looking image of insects' eyes, pollen grains or computer-chip circuits.

Both need a vacuum (air would scatter the electrons), and samples must be specially prepared.

Canadian connection: in 1938, graduate students James Hillier and Albert Prebus, working under Eli Franklin Burton at the University of Toronto, built the first practical electron microscope in North America. Hillier later helped develop the first commercial electron microscopes in the United States.

Impact: electron microscopes let scientists see viruses for the first time, study materials atom by atom and inspect computer chips. A recent technique, cryo-electron microscopy (samples flash-frozen; recognized by the 2017 Nobel Prize in Chemistry), maps the 3-D shapes of proteins. It was used in 2020 to map the spike protein of the virus that causes COVID-19, which helped vaccine and drug design.

Quantum computing

An ordinary computer stores information in bits, each exactly 0 or 1. A quantum computer uses qubits: two-level quantum systems such as tiny superconducting circuits, trapped ions, or photons.

• Superposition: a qubit can be in a combination of 0 and 1 at the same time, described by a wave function. Measuring it gives 0 or 1, with probabilities set by the state (the probability interpretation from lesson 11).
• Entanglement: qubits can be linked so their measurement results are correlated in ways no classical bits can be.
• Interference: a quantum algorithm is designed so that the probability waves for wrong answers cancel and those for the right answer add up, so measurement is likely to give the right answer.

The description of n qubits needs 2ⁿ numbers. 300 qubits would need 2³⁰⁰ ≈ 10⁹⁰ numbers, more than the estimated number of atoms in the observable universe (about 10⁸⁰). That is why ordinary computers cannot simulate large quantum systems, and why a quantum computer could help with problems such as designing new molecules, materials and medicines.

Where things stand (2026): machines with hundreds of qubits, and a few with more than a thousand, exist, but qubits are fragile: heat, vibration and stray fields cause errors. Most superconducting machines must be cooled to a few thousandths of a degree above absolute zero. Researchers have demonstrated quantum error correction, combining many physical qubits into more reliable "logical" qubits, and building large error-corrected machines is the main challenge today. The 2025 Nobel Prize in Physics went to John Clarke, Michel Devoret and John Martinis for experiments showing quantum tunnelling and quantized energy levels in an electric circuit large enough to hold in your hand, the physics behind superconducting qubits.

Encryption, risks and society

Much online security (banking, email, shopping) uses encryption that relies on how hard it is to factor very large numbers. In 1994 Peter Shor showed that a large, error-corrected quantum computer could factor them quickly. No existing quantum computer can do this yet, but data stolen today could be decrypted in the future ("harvest now, decrypt later"). In 2024 the U.S. National Institute of Standards and Technology published the first standards for post-quantum cryptography, and governments and banks, including in Canada, are working to switch over.

Quantum physics also offers new security: quantum key distribution uses single photons, so any eavesdropper disturbs them (measurement changes a quantum state) and can be detected.

Canada is a world centre for quantum research. The Institute for Quantum Computing (University of Waterloo) and the Perimeter Institute for Theoretical Physics (Waterloo) were founded around the turn of the century; D-Wave, founded in British Columbia, sold one of the first commercial quantum computers in 2011; Xanadu, founded in Toronto, builds photonic (light-based) quantum computers; and the federal government launched a National Quantum Strategy in 2023. The United Nations declared 2025 the International Year of Quantum Science and Technology, 100 years after the first papers of modern quantum mechanics.

Questions society faces: Who pays for and owns very expensive quantum machines, and who benefits? How quickly must privacy protections change? Will Canada keep its researchers and companies, or lose them to other countries? How do we avoid hype (overstated claims) while investing sensibly? Thinking through such questions is part of being scientifically literate.