Quantum Glossary

Anyon – A type of quasiparticle that occurs in 2D systems and exhibits unique quantum statistics distinct from fermions and bosons. Anyons play an important role in topological quantum computing.

Attoscale – Intervals on the order of 10⁻¹⁸, which is vital for studying some quantum phenomena.

Automatic polarization compensation – A technique that adjusts and stabilizes the polarization state of photons and/or quasiparticle spins to ensure optimal performance.

Bell’s Theorem – The idea that no theory based on local hidden variables can reproduce all predictions of quantum mechanics, implying that quantum correlations (entanglement) cannot be explained classically.

Bloch sphere – A visual representation of a qubit’s state in quantum mechanics. Points on the sphere represent different quantum states to provide a simplified visualization of qubit behavior.

Boson – A type of particle in quantum physics that follows Bose-Einstein statistics. A boson can occupy the same space and energy state as other bosons, enabling phenomena such as superfluidity and laser action. When two identical bosons are exchanged, the overall quantum wave function is unchanged, distinguishing them from fermions and anyons.

Braiding – The process of intertwining sets of quasiparticles (e.g., non-Abelian anyons) to manipulate their quantum states. Braiding is essential for achieving fault-tolerant quantum computations for some technology platforms.

Broadband polarization – The varying polarization states of light across a wide range of frequencies, important for enhancing communication and sensing technologies.

Chandelier – A type of optical experiment configuration used to study quantum phenomena and enhance measurement precision, often involving multiple light paths or beams. (Also known as a specialized wiring structure used to connect and cool a quantum processor inside a dilution refrigerator.)

Chiral edge modes – 1D states that exist at the boundaries of certain 2D materials. These modes allow current to move in only one direction.

Classical – Systems, concepts and theories based on traditional, non-quantum physics with rules of nature that apply to objects heavier than the mass of electrons.

Coherence – The synchronization between quantum states that enable superposition and interference, which are critical for quantum computation and secure communication.

Commute – Refers to the order of operations. When two actions commute, their sequence doesn’t affect the outcome, which is key in understanding quantum states and measurements.

Conserved quantity – A property (e.g., energy, momentum) that remains constant in an isolated system. Conserved quantity plays a key role in understanding fundamental interactions and behaviors.

Dark matter – An unseen form of matter that does not emit light or energy but still exerts gravitational effects. Dark matter plays a key role in shaping the universe and its overall structure.

Decoherence – Occurs when a quantum system interacts with its environment, causing it to lose its quantum characteristics and behave more like a classical system, which can hinder quantum technologies.

Degradation – The deterioration in quality or effectiveness of quantum states and systems over time. Degradation adversely affects the performance of quantum computing, communication, and sensing. Closely related to decoherence.

Degrees of freedom – The independent variables that characterize a quantum system’s state (e.g., position, momentum, or spin). These variables are essential for analyzing a quantum system’s behavior and properties.

Dilution refrigerator – A specialized cooling device that achieves ultra-low temperatures—close to absolute zero—which is critical for exploring quantum effects and operating superconducting qubits.

Dynamical decoupling – A special pulse sequence used for removing low-frequency noise from a qubit and extending its effective decoherence time.

Edge computing – Performing data processing near the point of data generation (at or near deployed quantum sensors), which minimizes delay, improves efficiency, reduces data transmission, and ensures timely analysis.

Entanglement – A quantum phenomenon in which the states of two or more particles become quantumly correlated in such a way that the state of each particle cannot be described independently of the others, even when separated by large distances.

Entanglement distribution – The process or mechanism of creating, distributing, and maintaining entangled states over distances, usually through the use of quantum repeaters. It involves the practical steps taken to generate and share entanglement and is used in quantum communication and networking.

Error correction – A method to detect and fix errors in quantum states caused by noise or environmental disturbances. Error correction ensures accurate computations and reliable quantum information processing.

Evolution – How a quantum system changes over time, as described by its wave function. This process reveals the dynamics and interactions of particles in quantum mechanics.

Excited state – When a quantum system (e.g., atom or molecule) is in a higher energy configuration than its ground state. It plays a key role in phenomena such as light emission and chemical reactions.

Exciton condensate – A state of matter formed when excitons (see bound electron-hole pairs) condense at low temperatures and exhibit unique quantum behaviors such as superfluidity in semiconductors.

Fault-tolerant – Fault-tolerant refers to systems that can continue functioning correctly even when some qubits have errors. Fault tolerance is crucial for reliable quantum computing, in which errors often arise from decoherence and noise.

Fermion – Particles (e.g., electrons, quarks) that have half-integer spins. Unlike bosons, fermions cannot occupy the same quantum state  (e.g., position, momentum, and spin).

Fidelity – The measurement of how closely a quantum state resembles a target or ideal state. Fidelity describes the precision of quantum operations and the quality of information processing in quantum systems.

Flow – The movement of particles or information in quantum systems, particularly in phenomena such as quantum entanglement or superfluidity. Flow highlights dynamic behaviors.

Gates – Fundamental operations that manipulate qubits. Gates are analogous to logic gates in classical computing and enable complex calculations and quantum algorithms.

Good quantum number – A property that remains unchanged during the evolution of a quantum system, helping to simplify calculations and understand the system’s symmetries and conserved quantities.

Ground state – The lowest energy configuration of a quantum system (e.g., atom or molecule). Ground is the most stable state, and electrons reside here until energy is added to excite them.

Grover’s algorithm – A quantum algorithm that provides a quadratic speedup for searching an unstructured database. This algorithm can find a marked item significantly faster than classical methods.

Hamiltonians – Key mathematical operators in quantum physics that represent a system’s total energy and are crucial for predicting how quantum states change and evolve over time.

Heterodyne detection – A technique that mixes a signal with a local oscillator to convert it to a more manageable frequency, thereby allowing precise measurement of signals in quantum optics and communications.

Heterostructures – The combination of different materials used to control the interaction between component material or to induce new emergent phenomena at the boundary of the layered materials.

Hyperentanglement – A phenomenon in which particles are entangled across several properties (degrees of freedom), such as polarization and momentum, enhancing quantum communication and computing capabilities.

Ion trap – A device that uses electromagnetic fields to confine and manipulate charged particles, called ions (typically atomic or molecular ions), within a small space.

Josephson junctions – Thin layers of insulating (non-superconducting) material sandwiched between two superconductors. At these junctions, the Josephson effect produces unique current-voltage relationships and behaviors that enable quantum devices.

Key generation – The process of creating secure encryption keys by using quantum principles and ensuring security through methods such as quantum key distribution.

Lattice – A structured arrangement of points in space commonly used to represent the layout of atoms in solids and to study particle interactions in condensed matter physics.

Majoranas – Particles that are their own antiparticles, theorized in quantum physics for robust qubits, and offer potential for topological quantum computing and fault tolerance.

Many-body systems – Systems with multiple interacting particles, the collective behaviors of which can lead to complex phenomena such as quantum phase transitions and emergent states.

Measurement – The process of observing a property of a quantum system—a process that also affects its state. Measurement collapses the wave function, thereby determining outcomes such as position or momentum.

Metastructure – Engineered materials with designed properties at various scales and often used to control light and wave behavior in quantum technologies, thereby enhancing sensors and communication devices.

Microring resonator – A small, circular waveguide that traps light to enable enhanced interaction with photons. A mircoring resonator is used in quantum optics, photonic circuits, and integrated optical systems.

Nanometrology – The measurement science focused on the nanoscale. Nanometrology is essential for advancing quantum science and technology by ensuring accuracy in the study of quantum materials and systems.

Nanoscale – The range of 1 to 100 nanometers (a nanometer is 1-billionth of a meter, or 10-9 meters), at which materials show unique quantum behaviors. The nanoscale is essential for creating cutting-edge quantum technologies and devices.

Nanostructure – A material or device with dimensions on the nanoscale, often exhibiting unique properties that are vital for advancements in quantum technology and next-generation applications.

Neutrinos – Tiny, electrically neutral particles that interact weakly with matter. Neutrinos play a key role in quantum physics and astrophysics and are pivotal in studying fundamental forces and cosmic events.

No Cloning Theorem – The idea that it is impossible to create an identical copy of an unknown quantum state. This principle ensures the security of quantum information and underlies quantum computing.

Noise – Fluctuations that interfere with measurements and signals, thereby impacting the performance and accuracy of quantum technologies and experiments.

Non-Abelian – A type of quasiparticle that arises in certain 2D quantum systems (see Anyon), the exchange of which (braiding) leads to changes in the system’s quantum state—changes that depend on the order of the exchanges and cannot be described by simple phase factors.

Operator – A mathematical tool that changes quantum states to provide measurable properties (e.g., position, energy) and is essential for analyzing and predicting quantum behavior.

Photonic – Relates to the use of photons, or light particles and/or waves. In quantum technologies, photons are often crucial for quantum communication, computing, and sensing.

Polarization splitter-rotator – A device that manipulates polarization of light by separating or rotating different polarization states, which is vital for controlling quantum bits in photonic quantum systems.

Probes – Tools or particles used to investigate quantum systems and provide insights about their properties and behaviors through measurement and interaction.

Quantum advantage or quantum supremacy – Proof that a programmable quantum device solves a well-defined task faster or with fewer resources than any known classical method.

Quantum algorithm – A set of step-by-step instructions designed to perform a specific computation on a quantum computer that utilizes the principles of quantum mechanics, such as superposition and entanglement, to solve a set of complex problems more efficiently than traditional methods.

Quantum annealing – An optimization technique that uses quantum fluctuations to find the lowest energy state of a system.

Quantum channel – A medium through which quantum information is transmitted, such as photons in optical fibers (or free space) or superconducting qubits in microwaves.

Quantum circuit compilation – A process that translates high-level quantum algorithms into sequences of operations on qubits to optimize them for execution on quantum devices.

Quantum compression – Techniques used to reduce the amount of quantum information transmitted without loss of fidelity, thereby enhancing the efficiency of quantum communication and storage systems.

Quantum computer – A type of computer that uses the principles of quantum mechanics to perform calculations to solve a set of complex problems more efficiently than classical computers.

Quantum cryptography – A secure communication method that uses quantum mechanics to protect information and ensure privacy through principles such as entanglement and the unpredictability of quantum states.

Quantum Key Distribution (QKD) – A secure communication method that uses quantum mechanics to share encryption keys, thereby ensuring that eavesdropping can be detected.

Quantum materials – Materials for which classical and effective theories fail and quantum mechanics is required to understand behavior at the macroscale. These include topological materials, some 2D materials, and correlated materials such as superconductors, for which  electron-electron interactions produce collective behaviors.

Quantum optimization – A process that seeks to find the best solution among many possible options by using quantum algorithms, which promise significant speedups over classical methods.

Quantum phenomena – Observable events or behaviors (e.g., entanglement, superposition) that showcase the unique properties of quantum systems.

Quantum process tomography – A technique that reconstructs the quantum state transformations of a system by analyzing measurement outcomes based on various input states to provide insights into quantum operations.

Quantum Processing Unit (QPU) – The core component of a quantum computer. QPUs perform quantum computations by manipulating qubits through quantum gates. Often used in the context of a large quantum computer (akin to a CPU in a classical computer) or as an accelerator in classical computing (like a GPU).

Quantum randomness – The inherent unpredictability in and non-deterministic properties of quantum measurements, which are utilized in secure communications and random number generation.

Quantum repeater – A device that boosts quantum signals over long distances. Repeaters are crucial for creating reliable quantum networks by enabling entanglement distribution between nodes.

Quantum sensors – Devices that utilize quantum phenomena (e.g., superposition, entanglement) to achieve ultra-high precision measurements to outperform classical sensors in various applications.

Quantum spin liquid – Materials in which magnetic orientations remain disordered and vary even at extremely low temperatures because of quantum fluctuations. These materials could lead to unique properties that are useful for quantum computing and materials science.

Quantum volume – A metric that measures a quantum computer’s capability by considering both the number of qubits and how effectively they can interconnect and operate.

Quasiparticles – Entities that arise in a medium and behave like particles. Quasiparticles play key roles in the properties of quantum materials.

Qubit (or quantum bit) – The basic unit of quantum information (akin to a classical bit) that can exist in two states simultaneously due to superposition.

Qubit recycling – A technique that reuses qubits during computation to improve resource efficiency and increase the performance of quantum computations.

Qudit – A quantum system composed of more than two states that can exist in a superposition. Qudits enable richer information encoding and processing in quantum systems.

Rashba states – Specialized energy levels for different electron spins created by strong spin-orbit coupling in materials. Rashba states enable precise spin manipulation in spintronics and quantum technologies.

Semiconductor – A material with electrical conductivity between that of conductors and insulators. Semiconductors are essential for building components of quantum devices.

Sensitivity – The minimum external signal that can be measured by a quantum sensor in 1 second.

Shor’s algorithm – A quantum algorithm used to efficiently factor large numbers. Developed in 1994 by Peter Shor, it is one of the most famous quantum algorithms.

Skyrmion – Tiny, stable, and whirlpool-like configurations of magnetic spins in materials. Skyrmions could be leverages for efficient data storage and transmission in some quantum applications.

Spectroscopy – A method for studying matter and/or particles by examining the interactions with electromagnetic radiation (often lasers) to help improve the understanding of quantum states and energy levels.

Spin – An intrinsic form of angular momentum carried by quantum particles (e.g., electrons). Spin is crucial for encoding information in quantum computing and technology.
State preparation – The process of setting a quantum system into a specific, desired state. State preparation is crucial for experiments in quantum computing and quantum communication to enable control over quantum properties.

Superconductor – A material that can conduct electricity without resistance when cooled below a certain temperature. This unique property stems from quantum mechanics.

Superfluidity – A state of matter in which liquids flow without viscosity at extremely low temperatures, revealing unique quantum properties that may advance technology and our understanding of physics.

Superposition – The phenomenon in quantum mechanics in which a quantum system exists simultaneously in multiple possible states until measured or observed.

Surface code – An error-correcting method that uses qubits arranged on a 2D lattice. This is the leading architecture for large-scale, fault-tolerant qubits and enables more robust quantum computations and communication.

Teleportation – Quantum teleportation is a process that transfers an unknown quantum state from one location to another by using entanglement and classical communication without physically moving the particles themselves.

Topological materials – Materials with special characteristics that arise from their quantum-level structure, making them valuable for cutting-edge technologies such as quantum computing and energy-efficient devices.

Topology – Properties of materials that remain unchanged under continuous transformations. Topology is crucial for understanding quantum phases and sophisticated quantum computing systems.

Trapped ion – Charged atoms or molecules held in place by electromagnetic fields. Trapped ions are used in quantum computing for storing and processing information by leveraging their precise control and coherence properties. Also seen in spectroscopy, quantum networking, quantum sensing, and clock applications.

Uncertainty Principle – States that certain pairs of physical properties (e.g., position, momentum) cannot be precisely measured simultaneously, highlighting quantum limits to our knowledge of the physical world.

Vortex – A swirling motion in superfluids or Bose-Einstein states. The flow is organized in distinct, fixed patterns and exhibits unique properties at low temperatures.

Wavelength – The distance between consecutive peaks of a wave. Wavelength is important in quantum contexts for describing the properties of light and other electromagnetic radiation.

X-basis – A set of quantum states defined by the superposition of traditional computational states. The X-basis is useful for describing and understanding many quantum algorithms.

Young’s double-slit experiment – This experiment reveals that light and particles act like waves when not observed but behave like particles when measured. The experiment highlights the oddities of quantum mechanics.

Z-basis – A set of quantum states usually associated with the spin or polarization of particles. The Z-basis is commonly used in quantum computing and information to represent qubits.

Zeno effect – A phenomenon in which frequent measurements prevent a quantum system from evolving, effectively “freezing” its state. This demonstrates the impact of observation on quantum systems.