Quantum Essentials · Module 1 · Introduction
What is quantum technology, and why now?
You're probably holding several quantum devices right now. Let's find them.
The short answer (tap to open)
Quantum technology uses the rules of the very small to do things ordinary physics can't. You already use the first wave every day: chips, LEDs, lasers, GPS clocks and MRI scanners. The new wave controls single atoms and particles of light to build quantum computers, precise sensors and secure communication. Governments are now spending billions on it.
Predict
How many parts of your phone only work because of quantum physics?
After this page you can
- name at least five quantum technologies you already use;
- say what's different about the new wave;
- name the three families: computing, sensing and communication;
- give three reasons this is happening now.
Part A
What quantum technology do you already use?
Quantum physics is the set of rules that atoms, electrons and light follow. Physicists worked those rules out between 1900 and 1927. Engineers then spent the next hundred years building with them. Your phone is full of the results.
Tap a glowing spot on the phone.
All six, in words
The chip: transistors.
The quantum idea: electrons in a solid can only have certain energies.
Your phone's processor holds billions of transistors. Each one is a tiny switch that lets current through or blocks it. Silicon makes a good switch because of a quantum rule: its electrons sit in bands of allowed energy, with a gap between them. Add a trace of the right impurity and you control which electrons can move. Ordinary physics can't explain why silicon behaves like this. Quantum physics can. Bell Labs built the first transistor in 1947, and every computer since depends on it.
The screen: light of an exact colour.
The quantum idea: when an electron drops to a lower energy, it gives off light of one exact colour.
Each pixel in your screen holds tiny light sources, LEDs or OLEDs. Inside them, electrons fall from a higher energy level to a lower one. Each fall releases a particle of light, called a photon. The size of the drop sets the colour. Engineers choose materials with exactly the drops they need for red, green and blue.
The camera: counting light.
The quantum idea: light arrives in packets, called photons.
Each pixel in your camera sensor is a tiny bucket for light. When a photon hits the silicon, it can knock an electron loose. The sensor counts the electrons, and that count becomes the brightness of the pixel. Albert Einstein explained this in 1905. It's what his Nobel Prize was for, not relativity.
Your location: atomic clocks in space.
The quantum idea: atoms switch between two energy levels at a fixed, exact rate.
Your phone finds you by timing signals from GPS satellites. Light travels about 30 centimetres in a billionth of a second, so the timing has to be extremely precise. Each satellite carries atomic clocks. They count the steady switching of caesium or rubidium atoms between two energy levels. No pendulum or crystal comes close.
Storage: crossing a wall.
The quantum idea: an electron can pass through a barrier it doesn't have the energy to climb. Physicists call this tunnelling.
Your photos sit in flash memory. To store a bit, the chip pushes electrons through a thin layer of insulator and traps them on the other side. By the rules of everyday physics they can't get through. By quantum rules they sometimes can, and engineers have learned to control how often.
Face unlock: a tiny laser.
The quantum idea: one photon can trigger an atom to release a second, identical photon.
Face unlock projects thousands of invisible dots from a tiny laser. A laser works because a photon passing an excited atom can trigger it to release an identical photon, in step with the first. Einstein predicted this in 1917. The first laser shone in 1960. Lasers now carry your broadband through optical fibre, read barcodes and cut steel.
6 of 6. And it isn't only your phone. MRI scanners read the magnetism of protons in your body. Solar panels turn photons into current. All of this is quantum technology.
Part B
So what is quantum physics?
What are the rules of the very small?
Quantum physics is the most precisely tested theory in science. Some of its predictions match experiment to better than one part in a billion. It isn't vague and it isn't mystical. It's a set of rules, and they're explainable.
Three ideas carry most of this course:
- Things come in steps. An electron in an atom can't have any energy it likes. It sits on one of a set of levels, like rungs on a ladder. That's why atoms give off exact colours, and why atomic clocks keep exact time. Chapter 1.
- Before you measure, you can only know the odds. A quantum system can be in a state that gives, say, a 70% chance of one result and 30% of another. Measure it and you get one result. Repeat the experiment a thousand times and the results match the odds exactly. Chapters 2 and 3.
- You can link two systems. Measure one and you learn something certain about the other, however far apart they are. You can't use this to send a message. You can use it for computing and for security. Chapter 5.
Why the rules feel unfamiliar. Everyday objects hold trillions upon trillions of atoms. Their quantum behaviour averages out into the smooth physics you see. The rules don't change at large sizes. They just get hidden in the crowd. Quantum technology works by keeping a few particles out of the crowd.
Part C
What changed? From crowds to single particles
What is the second quantum revolution?
Everything in Part A uses quantum effects in bulk. A chip moves billions of electrons at once. A laser beam holds countless photons. Engineers never needed to control any single one.
The new wave is different. It controls one atom, one electron or one photon at a time, and keeps its quantum state intact while it works. That's much harder. A single atom loses its state the moment heat, light or a stray magnetic field disturbs it. So the machines run colder than deep space, inside vacuums, or with light guided through chips.
Physicists call this the second quantum revolution. The first gave us the transistor and the laser. The second gives us three new families of technology.
How did we get here?
1900
Max Planck: energy comes in steps
Planck solved a puzzle about glowing objects by assuming energy comes in small fixed packets. Quantum physics starts here.
The whole timeline, in words
- 1900. Max Planck: energy comes in steps. Planck solved a puzzle about glowing objects by assuming energy comes in small fixed packets. Quantum physics starts here.
- 1905. Einstein: light comes in photons. Einstein explained how light knocks electrons out of metal. Your camera works the same way.
- 1925 to 1927. The full rules. Heisenberg, Schrödinger, Born and others wrote the complete theory. 2025 marked its hundredth year.
- 1947. The transistor. Bell Labs built the first transistor. The computer age begins.
- 1960. The laser. Theodore Maiman fired the first laser.
- 1970s. MRI. Scanners start reading the magnetism of protons inside the body.
- 1978. GPS satellites. The first GPS satellites launch with atomic clocks on board.
- 1994. Shor's algorithm. Peter Shor shows a quantum computer could break the encryption that protects the internet. The race begins.
- 1995. The first quantum logic gate. A team at NIST in the US runs the first quantum logic operation on single trapped atoms.
- 2012. Nobel Prize. Serge Haroche and David Wineland, for measuring and controlling single quantum systems.
- 2019. "Quantum supremacy". Google's Sycamore chip finishes one narrow task faster than the best supercomputers could. Chapter 11 looks at the arguments that followed.
- 2022. Nobel Prize. Alain Aspect, John Clauser and Anton Zeilinger, for experiments with linked (entangled) photons.
- 2024. Error correction works. Google's Willow chip shows errors falling as its error-correcting code grows. NIST publishes the first post-quantum encryption standards.
- 2025. Nobel Prize, and the International Year of Quantum. John Clarke, Michel Devoret and John Martinis, for quantum behaviour in an electric circuit big enough to see. Their work underpins today's superconducting quantum computers.
- 2026. The UK commits up to £2 billion. The government announces up to £2 billion for quantum, aiming to make and deploy quantum computers at scale in the UK by the early 2030s.
Part D
What are the three families of quantum technology?
The second revolution splits into three families. They use the same physics in different ways, and they're at very different stages.
Quantum computing: what is it for?
What it does: a quantum computer stores information in qubits, which can hold quantum states, not just 0 or 1. For certain problems, it can reach the answer in far fewer steps than any ordinary computer.
Which problems: simulating molecules and materials, which nature does in quantum terms; breaking some kinds of encryption; and some search and optimisation tasks. It is not faster at everything. It won't replace your laptop.
Where it stands: today's machines are small and make frequent errors. In 2024 Google showed that error correction can work at scale: errors fell as the code grew. Researchers are still testing whether one can beat ordinary computers on a useful real-world problem. Chapters 7 to 11.
Quantum sensing: what can it measure?
What it does: a single atom or electron reacts to the smallest change around it. Quantum sensors turn that sensitivity into measurement.
Examples: atomic clocks; gravimeters that sense rock, water or tunnels underground; magnetometers in wearable brain scanners, developed in the UK, that read the brain's tiny magnetic fields; and navigation that works when GPS is jammed.
Where it stands: the most mature of the three. Atomic clocks have run the world's timekeeping for decades, and quantum gravimeters are on sale today. Chapter 12.
Quantum communication: what does it protect?
What it does: it uses single photons to share secret keys. Any eavesdropper disturbs the photons and gets caught.
Where it stands: working links exist. China built a 2,000-kilometre network between Beijing and Shanghai and launched a quantum satellite, Micius, in 2016. Networks are still short and expensive.
The twist: the main defence against quantum attack isn't quantum at all. It's new ordinary maths, called post-quantum cryptography, that quantum computers can't break. The US standards body NIST published the first three standards in August 2024. Chapter 13.
Now, next, later or never?
Now
Next
Later
Never
Atomic clocks keep GPS working
The answers, in words
- Atomic clocks keep GPS working: Now. Running since the first GPS satellites in 1978.
- A quantum sensor maps what's under a road before digging: Next. Quantum gravity sensors are on sale and in field trials; one found a hidden tunnel under a road in 2022. Routine road surveys come next.
- Banks link two offices with quantum-secured keys: Now, small scale. Short links exist. Wide networks don't yet.
- A quantum computer designs a new medicine: Later. The strongest long-term case, but it needs large error-corrected machines.
- A quantum computer breaks today's internet encryption: Later. Not possible yet. Estimates of what it would take keep falling, so the switch to new encryption has started already.
- A quantum computer replaces your laptop: Never. It solves certain problems, not everyday ones. You'll use it, if at all, through the cloud.
Part E
Why is this happening now?
What's changed in the last few years?
- Control got good enough. For decades, single atoms and photons lost their quantum states too fast to compute with. Better materials, lasers and cooling have pushed error rates down, and error correction has started to work. Three Nobel Prizes since 2012 mark the progress.
- The money arrived. In March 2026 the UK announced up to £2 billion for quantum, aiming to make and deploy quantum computers at scale by the early 2030s. Investors put about $12.6 billion into quantum start-ups in 2025, more than six times the year before, according to McKinsey. The US, the EU, China, Japan and others run their own national programmes.
- There's a deadline. Someone can record encrypted data today and decrypt it once a big enough quantum computer exists. Security experts call this "harvest now, decrypt later". So organisations are switching to post-quantum encryption now. The UK's National Cyber Security Centre has set the timeline: plan by 2028, move the most important systems by 2031, finish by 2035.
- A hundred years on. 2025 marked a century since physicists wrote the full rules. The UN named it the International Year of Quantum Science and Technology. Public attention followed.
Your route
What brings you here?
Myths and media
Media check
Right, half right or wrong? Call it first.
Card 1 of 3
A product label: "Quantum" shampoo, a "quantum" car, a "quantum" supplement.
The claim: It uses quantum physics.
Check
Three quick ones
Collect
Your aha card
Quantum is already everywhere.
The new part is controlling single atoms and photons, for computing, sensing and communication.
Next page · Chapter 1
Why does the small world come in steps?
Atomic clocks, lasers and LEDs all rest on one idea. Next, we see why energy comes in steps.
Next page