The quantum in your pocket
Lesson 5 of 23 in the course “Quantum”. Free, with animations and a quiz.
Your phone is a quantum device
Quantum physics isn’t only about the future. Without it there’d be no smartphone. The chip, storage, camera, screen, Face ID and GPS all run on effects only quantum physics explains: energy steps, tunnelling, photons. Engineers have used these rules for 70 years. Next we’ll go through each part and see why the qubit is the next step, not sci-fi out of nowhere.
The transistor: 19 billion taps
A transistor is a tiny tap for electrons: open means 1, closed means 0. Apple’s A17 Pro chip has 19 billion of them. Why can silicon sometimes conduct and sometimes not? Ordinary physics can’t explain it. Quantum theory gave the answer: electrons in a crystal have allowed and forbidden energy bands, the same steps from the first lesson. Without that theory there wouldn’t be a single computer. By the way, a transistor’s ordinary bit is exactly the 0 or 1 we’ll compare the qubit with.
Lasers and Face ID
In 1917 Einstein noticed that a photon can “persuade” an excited atom to release an identical photon, same colour, same direction. In 1960 the first laser was built on that idea. An ordinary bulb shines photons every which way; a laser gives an army of identical ones. Where you’ll find it: the barcode scanner at the checkout, fibre-optic internet and Face ID. Face ID projects more than 30,000 invisible laser dots onto your face and builds a 3D map from them.
GPS runs on atomic clocks
Your phone finds you using satellite signals: it compares when each signal left and when it arrived. Light travels 300 metres in one millionth of a second. So the clocks have to be insanely precise. Satellites carry atomic clocks: they count an electron’s jumps between steps in a caesium or rubidium atom. Since 1967 the second has officially equalled 9,192,631,770 cycles of caesium radiation. Without quantum steps, navigation would miss by kilometres.
The hospital, the bulb, the TV
An MRI sees organs through the hydrogen nuclei in your body. Each nucleus has spin, a quantum property that acts like a tiny magnet. A superconducting magnet lines the spins up, and radio waves make them “ring”. The blue LED, without which there’d be no white LED bulbs or screens, won Japanese scientists the 2014 Nobel. And quantum dots in QLED TVs glow in pure colours; they earned the 2023 Nobel Prize in Chemistry.
The first and second quantum revolutions
Everything we’ve covered is the first quantum revolution. Transistors, lasers and clocks use quantum laws for huge crowds of particles at once. The second one is happening now: scientists have learned to control individual atoms, photons and electrons one by one, keep them in superposition and entangle them. That’s where quantum computers, quantum communication and ultra-precise sensors come from. In level two you’ll build a qubit yourself, apply gates and see interference in a trainer.
Check yourself
- Which of these works thanks to quantum physics?
Correct answer: All of them: the chip, Face ID and GPS. The chip’s transistors rely on quantum energy bands, Face ID on a laser, GPS on atomic clocks. The quantum has long been in your pocket, not just in the future. - Why can’t GPS do without atomic clocks?
Correct answer: An error of a millionth of a second is already 300 m. Position is worked out from the signal’s travel time. Light covers 300 m in a millionth of a second, so the clocks must be millions of times more precise than ordinary ones. - How is the second quantum revolution different from the first?
Correct answer: We control single particles and their superposition. The first revolution used quantum laws for crowds of particles. The second works with each particle individually: superposition, entanglement, qubits.