Quantum Technology: Applications and Implications

- Quantum and Quantum Theory

Very small particles and light behave differently from objects we encounter in normal life, which are described by classical mechanics and classical electrodynamics. The mechanics of light and matter at the atomic and subatomic scale are described by quantum theory, which forms the underlying principles of chemistry and most of physics. In its first centennial of existence quantum theory has already brought us the information age with its disruptive technologies of transistors, lasers, nuclear power, and superconductivity.

In physics, a quantum (plural quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a physical property can be "quantized" is referred to as "the hypothesis of quantization". This means that the magnitude of the physical property can take on only discrete values consisting of integer multiples of one quantum. 

For example, a photon is a single quantum of light (or of any other form of electromagnetic radiation). Similarly, the energy of an electron bound within an atom is quantized and can exist only in certain discrete values. (Atoms and matter in general are stable because electrons can exist only at discrete energy levels within an atom.) Quantization is one of the foundations of the much broader physics of quantum mechanics. Quantization of energy and its influence on how energy and matter interact (quantum electrodynamics) is part of the fundamental framework for understanding and describing nature.

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- Quantum Technology

Quantum technology is a class of technology that works by using the principles of quantum mechanics (the physics of sub-atomic particles), including quantum entanglement and quantum superposition. You don’t need to know exactly what quantum technology is to make use of it. Your smartphone is a type of quantum technology – its semiconductors use quantum physics to work – but neither you or the engineer who designed it need to know the ins and outs of quantum mechanics.

Quantum technology promises improvements to a vast range of everyday gadgets, including:

- Quantum Entanglement

Quantum entanglement is when two atoms are connected, or entangled, despite being separated. If you change the properties of one of them, the other changes instantly. In theory, this would be the case even if the entire universe separates the entangled atoms. If that wasn’t spectacular enough, quantum mechanics says simply observing an atom changes its properties. 

One possibility this creates is in enhancing the security of communication through quantum protected cipher keys. You can use entangled atoms to detect whether someone has interfered with the transmission of data. 

For example, you can have two entangled atoms with clockwise and anticlockwise ‘spins’. One atom is sent with the encryption key and if an eavesdropper intercepts the transmission, this causes a change in the ‘spin’ of the atom, affecting the overall quantum state of the system and resulting in the detection of the eavesdropping attempt.

- Quantum Superposition

The feature of a quantum system whereby it exists in several separate quantum states at the same time. For example, electrons possess a quantum feature called spin, a type of intrinsic angular momentum. In the presence of a magnetic field, the electron may exist in two possible spin states, usually referred to as spin up and spin down. Each electron, until it is measured, will have a finite chance of being in either state. Only when measured is it observed to be in a specific spin state. In common experience a coin facing up has a definite value: it is a head or a tail. Even if you don’t look at the coin you trust that it must be a head or tail. In quantum experience the situation is more unsettling: material properties of things do not exist until they are measured. Until you “look” (measure the particular property) at the coin, as it were, it has no fixed face up.

Quantum superposition is the theory that sub-atomic particles exist in multiple states simultaneously. It’s the crux of the Schrodinger’s Cat thought experiment - a cat, a flask of poison and a radioactive source are in a sealed box. If a Geiger counter detects radioactivity, it shatters the flask, releasing the poison and killing the cat. Since the radioactivity detection is a statistical process, the cat can be both alive and dead while the box is sealed, with the outcome only confirmed when you open the box and observe the cat to be in one state or the other. 

The practical application of this mind-bending version of reality is most obvious in quantum computers. While digital computers store data as bits (the ones and zeros of binary), quantum computers use qubits that exist as a one, zero or both at the same time. This superposition state creates a practically infinite range of possibilities, allowing for incredibly fast simultaneous and parallel calculations.

One of the properties that sets a qubit apart from a classical bit is that it can be in superposition. Superposition is one of the fundamental principles of quantum mechanics. In classical physics, a wave describing a musical tone can be seen as several waves with different frequencies that are added together, superposed. Similarly, a quantum state in superposition can be seen as a linear combination of other distinct quantum states. This quantum state in superposition forms a new valid quantum state.

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