Quantum computing definitions
Quantum computing is a newer form of computing that uses the principles of quantum mechanics to perform computing tasks. The following definitions will help you find your way around the strange but fascinating new world of quantum computing.
- Quantum mechanics: A different kind of physics than classical mechanics, which is what people encounter in their daily lives and expect from typical computers, known as classical computers. Quantum mechanical principles typically apply to very small particles, such as atoms, electrons, and photons. It works also with certain materials under extremes of temperature and pressure, such as certain metals when they’re supercooled (chilled to temperatures very near absolute zero) and arranged to alternately block or allow a current.
- Coherence: When matter that can operate under quantum mechanical principles is not directly observed, measured, or placed in contact with larger amounts of matter, it’s coherent: able to demonstrate quantum mechanical, rather than classical, properties such as superposition, entanglement, and tunneling.
- Superposition: A coherent particle can be in a multitude of states at the same time, and not in a definite state until it is measured. For instance, an electron in a state of superposition can have a spin — a magnetic property — that is neither up (1) nor down (0) until the spin is measured, at which point it takes on a spin of either 1 or 0, with equal probability.
- Entanglement: When two coherent particles are entangled, the state of one and the state of the other are linked, across all relevant measurements. For instance, if two electrons are entangled, measuring one of them and finding it at a state of 0 tells the experimenter that the other electron is at a state of 1, whether the other electron is very close or very far away.
- Tunneling: A coherent particle can tunnel, which means that it can appear in one place at a given instant and then appear at another place, potentially fairly distant in the very next instant. The particle does not pass through the space between the two locations. A tunneling particle is not affected or impeded by barriers placed between its initial location and its next location.
- Supercooling: Chilling certain materials, such as some metals or ceramics, very close to absolute zero can put them in what is called a supercooled state. In this state, the material has zero resistance to conducting a current and can demonstrate quantum mechanical properties, even though the material may be made up of millions or billions of atoms.
- Bose-Einstein Condensate: A Bose-Einstein condensate (BEC) is a gas under extreme pressure, or reduced to an extremely cold temperature, or both such that it demonstrates quantum mechanical behavior, even though the gas may be made up of millions or billions of atoms.
Kinds of Quantum Computing
Quantum computing today comes in several different flavors, each of which may be part of your journey into this new world of technology:
- Quantum simulator: A quantum simulator running on a classical computer — usually available through a cloud service online — can give you a running start into quantum computing at low or no cost.
- Quantum-inspired computing: Powerful high-performance computers (HPCs) running software algorithms that borrow ideas and approaches from the world of quantum computing are delivering useful results today, as “real” quantum computers gradually grow in capability.
- Quantum annealing: A quantum annealer is a less powerful type of quantum computer that is easier to build and run. It can handle a more limited range of problems than a gate-based quantum computer.
- Gate-based quantum computer: A gate-based quantum computer uses logic gates, like a classical computer, but of a different kind that performs quantum mechanically savvy steps.
Qubit types
Qubits are tiny bits of matter that display quantum mechanical properties and have control mechanisms, such as laser beams, microwave radiation, or magnetic fields.
The control mechanisms allow the qubit to be initialized (to an indeterminate quantum state), manipulated through programming steps (called logic gates in gate-based computing), and measured to produce a result, either 0 or 1 for each qubit.
Qubits can be placed in a state of superposition, can be entangled with one another, and can exhibit tunneling.
Following, are the types of qubits used in logic-gate quantum computers that have the most development, investment, and use today.
- Superconducting qubits: A superconducting qubit has at its core tiny bits of metal (but still containing a large number of atoms). The bits of metal are supercooled (chilled to very close to absolute zero). Microwaves and lasers are used for control. Quantum computers with superconducting qubits have the highest qubit counts, up to the low hundreds of qubits as of this writing.
- Trapped ion qubits: An atom that initially has a neutral electrical charge is ionized, that is, an electron is added or removed, giving the ion a positive charge (if an electron, which has a negative charge, is removed) or a negative charge (if an electron has been added). Having a charge makes the atom easy to trap using magnetic fields, with lasers also used for control. Quantum computers with trapped ion qubits have demonstrated high degrees of fidelity (accuracy in completing programming steps) and stability.
- Cold and neutral atom qubits: Non-ionized atoms can also be used as qubits by using lasers as the control mechanism.
- Photonic qubits: Photons — the energetic, massless particles that make up light — can be used as qubits by using lasers and other techniques as a control mechanism.
- Silicon spin: Electrons are trapped in tiny vacancies in silicon called quantum dots and are controlled by lasers and magnetic fields.
Learn more in online classes
Online classes teach quantum computing basics, quantum computer programming, and other valuable skills in quantum computing. Here are some leading options:
MIT Quantum Information Sciences: The online version of a class from the renowned Massachusetts Institute of Technology (MIT).
Quantum Cryptography: An affordable online class from the widely known California Institute of Technology (Caltech).
The Quantum Internet and Quantum Computers: How Will They Change the World?: An online course for beginners from Delft University in the Netherlands. Taught in English.
Understanding Quantum Computers: An online course covering fundamentals and mostly avoiding math.
Quantum Quest: A course for high-school students that uses the Discord online platform for course communications.
Quantum Machine Learning: A hands-on programming course from the University of Toronto.
Quantum Computing: Less Formulas — More Understanding: A solid introductory course from St. Petersburg University in Russia, taught in multiple languages.
Black Opal: A course from quantum computing company Q-Ctrl focusing on job training with a certification option.
