Quantum 101 » Sydney Quantum Academy

April 15 2026

Quantum Glossary

The Quantum 101 Glossary is your beginner-friendly guide to the fascinating world of quantum technology.

Quantum technology harnesses the unique properties of quantum mechanics to create groundbreaking innovations in computing, communication, sensing, cryptography, and beyond. Whether you’re new to the field or looking to deepen your understanding, this glossary will guide you through the essential terms and concepts of quantum technology.

Algorithm: A set of steps using coded instructions to solve a problem. Quantum algorithms use quantum properties such as superposition and entanglement to reduce the number of steps. Key areas where quantum algorithms are being investigated include cryptography and cybersecurity, chemistry simulation, materials and drug discovery, machine learning, optimisation problems, financial modelling and risk assessment. As quantum computing advances, researchers are actively exploring new quantum algorithms and applications across various domains.

Atom: The basic building block of all elements. An atom consists of protons and neutrons in a nucleus, and electrons around it. Atoms combine to form molecules and crystals, comprising all matter – including ourselves.

Atomic Clocks: Atomic clocks keep time by monitoring the electromagnetic signals that electrons in atoms emit when they change energy levels. This can be done very precisely, leading to very good clocks.

Bit: An abstraction for the smallest piece of information in classical computing, which can be either 0 or 1. Often realised as two different voltage levels in an electronic circuit.

Bloch Sphere: A 3D representation of a qubit’s state, where the spherical coordinates indicate the degree of superposition between 0 and 1 and the phase between them.

Circuit: A sequence of operations (gates, measurements, resets) performed on qubits to perform computation.

Classical Computer: A regular computer like the ones you use daily. Classical computers process information using combinations of bits. Everything you do on your computer is made possible by processing combinations of these bits in strings of zeroes and ones.

Code: In quantum computing, a code refers to a mathematical scheme where something useful and precious, i.e., some amount of quantum information, is hidden inside a bigger quantum system consisting of many small systems. It is widely used to correct errors in quantum computing.

Coherence: A measure of how well a quantum system can maintain its uniquely quantum properties, which is necessary for outperforming classical systems. Longer coherence is crucial for e.g. complex computations.

Decoherence: When a quantum system loses its uniquely quantum properties, usually due to interference from the environment. This interaction causes the system to behaviour more and more like a classical state, losing any quantum advantage it may have had . Understanding and mitigating this process is crucial for quantum technologies.

Deutsch’s Algorithm: One of the first examples demonstrating that quantum computers can solve certain problems faster than classical computers. It was proposed by physicist David Deutsch from University of Oxford.

Dirac Notation: A widely used notation in the mathematics of quantum mechanics and quantum technologies. It was introduced by theoretical physicist, Paul M. Dirac, one of the founders of quantum mechanics.

Double-Split Experiment: This experiment is a is a cornerstone example in quantum mechanics that demonstrates the wave-particle duality of light and matter. It highlights the key role that interference plays in quantum processes.

Electron: A subatomic particle found in all atoms. It has several properties that can be used as a qubit in quantum information, e.g. a “spin” of up or down.It is (negatively) charged and interacts strongly with other charges, which can be good for operations but bad for decoherence.

Eigenstate: A stable quantum state that remains unchanged when a measurement is made. Eigenstates are essential in understanding key differences between classical and quantum systems.

Entanglement: A quantum phenomenon where two or more particles become interconnected in such a way that the state of the pair cannot be described as a pair of states – the whole is in some sense more than the sum of its parts. This can lead to unintuitive behaviour, such as instaneous influences between paticles regardless of distance. Entanglement can often (but not always) be viewed as the resource that allows quantum technologies to outperform their classical counterparts – for example, it can be used to make more accurate measurements of gravitational waves. Interesting fact: Einstein coined the now popular phrase “spooky action at a distance” when describing entanglement.

Error Correction: A set of methods used in computing to protect information from errors caused by unwanted disturbances. This is especially important for quantum information, because of the susceptibility of quantum systems to decoherence. The fact that quantum error correction is possible is a key result that makes quantum technologies feasible.

Fault Tolerance: Fault tolerance in quantum computing refers to a system's ability to perform accurate quantum computations even in the presence of noise. It requires that error-correction and related techniques can avoid and/or detect and correct errors 'faster’ than the faults naturally occur. Fault-tolerant systems allow for the execution of complex algorithms over extended periods without the accumulation of errors that would otherwise render the computation incorrect.

Gate: Basic building blocks of circuits – for quantum computers, operations on qubits that alter their state. Quantum gates are reversible and usually operate on one or two qubits at a time.

Grover’s Algorithm: A key example of a useful quantum algorithm, it allows one to find items in a database more quickly (in fewer steps) than classical search algorithms.

Hadamard Gate: A quantum gate that puts a qubit into superposition of 0 and 1.

Hilbert Space: The type of mathematical space which is used to describe quantum states and operations.

Interference: When two waves overlap, they can reinforce or cancel each other out, creating interference patterns. We observe this phenomenon in relatively special circumstances classically (e.g. in fluids), but in quantum mechanics it is raised to a fundamental feature of all forces and particles. This is evident in the famous double-slit experiment, where particles exhibit both wave and particle behaviours.

Measurement: The process of observing a property of a system. In quantum mechancis measurements are associated with a set of particular states (eigenstates), each with a definite value for the observable property, for example checking if a qubit is in the state 0 or 1. The act of measurementforces quantum systems to randomly “collapse” into one of that observable’s eigenstates”, with a probability dictated by the pre-measurement state of the system. This discontinuous collapse behaviour differs markedly from quantum systems’ continuous behaviour when not observed, spurring debates amongst experts to this day on the special role of measurements in quantum mechanics.

Nanotechnology: The science, engineering, and application of materials and devices with structures, properties, and behaviours controlled at the nanoscale (typically between 1 to 100 nanometres). At this scale, materials can exhibit unique properties that differ significantly from their larger-scale counterparts, including enhanced strength, conductivity, reactivity, and optical characteristics. Interesting fact – an ant is about 5 million nanometres long. Nanotechnology is used to create advanced materials, such as stronger, lighter composites and more efficient energy storage systems, and in drug delivery, enabling targeted treatments at the cellular level. It also plays a significant role in quantum computing and sensing technologies, where quantum effects at the nanoscale improve performance and capabilities beyond classical systems.

Noise: Noise refers to any unwanted interaction or disturbance that disrupts the quantum state of qubits. This can arise from external environmental factors, such as temperature fluctuations, electromagnetic interference, or imperfections in the quantum system itself. Noise leads to errors and decoherence.

NISQ: Stands for "Noisy Intermediate-Scale Quantum." Refers to the current state of quantum computing, where full quantum error correction is not yet applied.

Photon:  A quantum of light, or more generally electromagnetic radiation; it is the basic unit that carries electromagnetic force.

Quantum Advantage: Quantum advantage refers to the point where a quantum computer outperforms classical computers in terms of speed or resource efficiency. In other words, solving problems that classical computers can't handle or solving problems more accurately with fewer resources.

Quantum Algorithm: A quantum algorithm is a sequence of quantum operations or instructions designed to solve specific computational problems by exploiting quantum mechanical properties like superposition and entanglement, allowing for faster solutions than classical algorithms for certain tasks.

Quantum Chemistry: Quantum chemistry is a branch of chemistry that applies the principles of quantum mechanics to study and understand the behavior of atoms, molecules, and chemical reactions at a microscopic level. It combines the concepts of quantum mechanics and chemical theory to explain the structure, properties, and reactivity of molecules enabling advancements in fields like material science, drug design, and nanotechnology. It also aids in understanding complex chemical reactions, enhancing the development of new materials, catalysts, and environmentally sustainable solutions.

Quantum Communication: A field within quantum physics that deals with the transmission of information encoded in quantum states of particles. It offers several advantages over classical communication, primarily in terms of security

Quantum Computing: A new type of computing that uses quantum bits (qubits) to process information in ways that classical computers cannot. Unlike classical bits, qubits don't just represent 0 or 1. Thanks to a property called quantum superposition, qubits can be in multiple states simultaneously. This means a qubit can be 0, 1, or both at the same time. This is what gives quantum computers the ability to process massive amounts of data and information simultaneously.

Quantum Cryptography: Leverages the principles of quantum mechanics to create unbreakable encryption methods and secure communications. Quantum cryptography can revolutionise how we secure online communications, such as emails, video calls, and financial transactions. Governments, military organisations, and corporations can use quantum cryptography to ensure that their communications cannot be intercepted or tampered with.

Quantum Key Distribution (QKD): A cryptographic protocol based on the uncertainty principle, where two parties exchange quantum states instead of electronic signals. QKD keeps information secure, even against an attack from a quantum computer.

Quantum Mechanics: Quantum Mechanics is the area of physics that studies the behaviour and interactions of particles at the smallest scales, such as atoms and subatomic particles. The principles of quantum mechanics are utilised in quantum computing for information processing.

Quantum Metrology: The science and practice of making highly accurate measurements based on quantum principles. It focuses on developing techniques and technologies to achieve measurements with unprecedented precision and accuracy. Quantum metrology has applications across various fields, including navigation, timekeeping, communication, and fundamental research.

Quantum Sensing: The precise measurement and detection of physical quantities using quantum systems, such as atoms, ions, or photons, to measure physical quantities with extremely high precision. These physical quantities could include magnetic fields, electric fields, gravitational fields, or even time itself. Quantum sensing takes advantage of the fundamental principles of quantum mechanics, such as superposition and entanglement, to achieve measurements that surpass the limitations of classical sensing methods. Examples of quantum sensing technologies include atomic clocks, magnetometers, and gravitational wave detectors.

Quantum Simulation: A technique used in quantum physics to simulate the behaviour of quantum systems using another controllable quantum system. It involves replicating the dynamics of a complex quantum system that is difficult to study directly, such as a large molecule or a condensed matter system, using a simpler, more controllable quantum system that can be manipulated in a laboratory setting. By engineering the interactions between the simulated system and the controllable quantum system, researchers can study the properties and behaviour of the simulated system under various conditions. Quantum simulation has the potential to provide insights into fundamental questions in physics, chemistry, and materials science, such as the behaviour of strongly correlated electron systems, the dynamics of chemical reactions, and the properties of exotic materials like high-temperature superconductors. It also plays a crucial role in the development of quantum technologies, such as quantum computers and quantum simulators, by providing a platform for testing and validating quantum algorithms and protocols.

Quantum Supremacy: When a quantum computer does something that a classical computer practically can’t.

Quantum Teleportation: A means of exchanging information over big distances, using particles that have been quantum entangled. Quantum teleportation has the ability to provide quantum connectivity securely between geographically distant nodes.

Qubit: A quantum bit or qubit is the basic unit of quantum information. Just like classical bits, a quantum bit must have two distinct states: one representing “0” and one representing “1”. Unlike a classical bit, a qubit, can exist as 0, 1, or both at the same time due to a phenomenon called superposition, and can even be entangled with other quantum bits. This ability to be in multiple positions at once is one of the reasons quantum computing holds the promise to be so powerful.  

Schrödinger’s Cat: A thought experiment derived by Austrian-Irish physicist Erwin Schrödinger to explain the concept of superposition. In this scenario, a cat is sealed inside a box with a device that has a 50% chance of killing the cat. Until the box is opened and the cat is observed, it exists in a superposition- both alive and dead at the same time. The cat’s state "collapses" to either alive or dead only once it is observed.

Superposition: A fundamental quantum principle where a quantum particle can exist in multiple states or positions simultaneously, rather than being limited to just 0 or 1. The state remains in superposition until a measurement is made, at which point it “collapses” into a specific state based on the type of measurement.

Teleportation: In the quantum world, teleportation isn’t science fiction; it’s a real phenomenon. It involves the transmission of quantum information from one location to another without physical movement.

Trapped-ion technology: A quantum computing approach using electromagnetic fields to trap charged ions (atoms) for information processing.

Tunnelling: Quantum particles can “tunnel” through energy barriers that classical physics suggests should be impenetrable. This phenomenon is critical in explaining how particles like protons can fuse in the sun despite lacking sufficient kinetic energy. Think “wormhole”

Wavefunction: A mathematical function that describes the quantum state of a system, like a blueprint for its behaviour, it contains all the information of a particle, such as its position, momentum, time and/or spin.