DID YOU KNOW? Unlike electrons, photons – as used in quantum cryptography and perhaps future computers – have zero mass
Introducing the people who dared to think the unthinkable, laying the foundations of quantum technology
Albert Einstein 1905 Einstein explained the photoelectric effect by suggesting that light took the form of discrete bundles called photons. This seemed at odds with light’s wave nature.
Louis de Broglie 1923 French physicist Louis de Broglie expanded on previous discoveries by proposing that all tiny particles can behave as waves, and vice versa.
I
Austrian physicist Erwin Schrödinger’s paper describing the motion of an electron as a wave function was a defining moment in quantum mechanics.
Werner Heisenberg 1925-1927 Alongside Niels Bohr, Werner Heisenberg suggested that subatomic particles only adopt a particular state when observed.
Alexander Holevo 1973 Russian mathematician Alexander Holevo was one of several researchers to lay down the theoretical foundations of quantum mechanics.
WWW.HOWITWORKSDAILY.COM
“The difference between classical physics and quantum mechanics is absolutely staggering”
Quantum concepts Examining the bizarre quantum effects that underpin quantum technology
Superposition Erwin Schrödinger 1926
Prize-winning physicist Niels Bohr is on record as saying “If anybody says he can think about quantum theory without getting giddy, it merely shows that he hasn’t understood the first thing about it.” We’ll look at some of these concepts in more detail in the boxout below, but, having made such an astonishing claim, it’s surely only appropriate to provide a couple of examples of apparently impossible quantum behaviour. Perhaps one of the most bizarre things that can happen in the subatomic realm is that objects such as electrons or photons can be in two places at the same time or in two different states at once – a so-called state of superposition.
A particle in superposition is in two states at once, so it could represent both a binary 0 and 1. Think of a coin: if it’s spinning you can see heads and tails simultaneously.
Entanglement Two entangled particles are strangely linked, so the fate of one affects the other. If you observe one particle this will cause its superposition to be lost, and the same will happen to its entangled twin.
CLASSICAL PHYSICS
QUANTUM PHYSICS
Heads OR tails
Heads AND tails
QUANTUM PHYSICS HEADS + HEADS HEADS + TAILS TAILS + HEADS TAILS + TAILS N quantum bits or qubits
2n possible states
Observation Observing a particle in superposition causes it to adopt a single state. Any interaction with the environment does the same. The more entangled the particles, the harder it is to maintain superposition.
Observation or noise
DIGITAL COMPUTING No cloning Making a copy of a particle in superposition also causes the superposition to be lost. This makes designing a quantum computer tricky, but, in quantum communications, it alerts the sender to the presence of an eavesdropper.
Copy or eavesdrop © Shutterstock; WIKI
The pioneers of quantum mechanics
t might be a term that trips off the tongue, and it may suggest a field of study dominated by the scientific elite, but quantum mechanics – or quantum physics if you prefer – is largely a mystery to the layperson. Surprisingly, therefore, it couldn’t be much simpler to sum it up, even though understanding it is considerably more difficult. Quantum mechanics is concerned with the behaviour of atoms, photons and the various subatomic particles, and it contrasts with classical physics, which describes the behaviour of everyday objects that are large enough to see. The difference between classical physics and quantum mechanics is absolutely staggering. The objects that we see in the world around us behave in a way that seems intuitive, but once we start to consider very small objects, intuition and common sense have to be abandoned. Instead, when we consider them individually, atoms, electrons and photons behave in a way that most people would be inclined to describe as impossible. That perception of impossibility isn’t a naive view either. Even the eminent Nobel
QUANTUM COMPUTING Copy or avesdrop How It Works | 013