What Is Quantum Information Science?

  • No math. No equations or messy formulas. Or math symbols. No matrices or vectors.
  • No Greek symbols.
  • No German. No long words that begin with “eigen”.
  • No physics jargon. Except to explain some of the terms, but in plain language.
  • No long list of famous names from physics.
  • No pictures or diagrams. Keep things simple.
  1. Quantum computing — includes hardware (quantum computers), software, algorithms, and applications.
  2. Quantum communication — includes quantum networking, quantum Internet, quantum cryptography, and quantum information theory.
  3. Quantum metrology and quantum sensing — includes detection of objects.
  • Quantum computing alone. This isn’t ideal, but it is a common usage.
  • Quantum computing and quantum communication together, but excluding quantum metrology and quantum sensing.
  1. Quantum mechanics.
  2. Quantum effects — see Quantum mechanics, but summarized here, later.
  3. Quantum physics — see Quantum mechanics.
  4. Quantum chemistry and Quantum computational chemistry (and here).
  5. Quantum biology.
  • Quantum information processing — not just quantum computing, but quantum communication, quantum networking, and quantum metrology and quantum sensing, or any subfield concerned with capturing, storing, manipulating, or communicating quantum information (quantum state).
  • Quantum information processing system — commonly a quantum computer, but generally any hardware system which is capable of processing quantum information.
  • Quantum-based technology — a loose reference to any technology which is based in whole or in significant part on some aspect of quantum information science.
  • Quantum technologies — sometimes used as a synonym for quantum information science.
  • Quantum technology, quantum technologies — another loose reference to any technology which is based in whole or in significant part on some aspect of quantum information science.
  • Quantum information technologies — ditto.
  • Quantum applications — It is ambiguous whether quantum applications are included under quantum information science specifically since the term quantum information science and technology is sometimes used when applications are to be included.
  • Quantum science — vague term which may may simply be a synonym for quantum information science, or refer to applications of quantum information science for the natural sciences, such as simulation of physics, chemistry, or biology. Or, it may simply be a synonym for quantum physics or quantum mechanics. It all depends on the context in which it is used.
  1. What is quantum information science?
  2. What’s so special about quantum information science?
  3. QIS
  4. What disciplines are involved with quantum information science?
  5. What is quantum?
  6. Quantum mechanics
  7. Quantum physics
  8. Quantum chemistry
  9. Quantum computational chemistry
  10. Quantum biology
  11. Quantum field theory
  12. Quantum theory
  13. Quantum system
  14. Isolated quantum system
  15. Quantum effects
  16. Quantum resource
  17. Quantum state
  18. Wave function
  19. Linear algebra
  20. Quantum information
  21. Measurement
  22. Qubit
  23. Quantum bit
  24. Qutrits, qudits, and qumodes
  25. Phase
  26. Interference
  27. Environmental interference
  28. Stationary qubits and flying qubits
  29. Quantum error correction (QEC)
  30. Logical and physical qubits
  31. Quantum programs, quantum logic gates, and quantum circuits
  32. Unitary transforms
  33. Quantum algorithms
  34. Algorithmic building blocks
  35. Hybrid quantum/classical algorithms
  36. Variational quantum algorithms
  37. Quantum computer as a coprocessor
  38. Quantum advantage and quantum supremacy
  39. Exponential speedup
  40. Quantum parallelism
  41. Quantum communication
  42. Quantum networking
  43. Quantum internet
  44. Quantum channel
  45. Quantum teleportation
  46. Quantum key distribution (QKD)
  47. Alice and Bob
  48. Quantum storage
  49. Quantum metrology and quantum sensing
  50. Quantum sensors
  51. Quantum-enabled sensors
  52. Quantum detection
  53. Quantum sensing and detection
  54. Quantum simulators
  55. Quantum-inspired computing
  56. Theory and practice
  57. Science and engineering
  58. Hardware and software
  59. Device
  60. NISQ device
  61. Fault-tolerant quantum computer
  62. Applications
  63. Algorithms
  64. Quantum simulation
  65. Natural sciences and quantum simulation
  66. What are the biggest factors holding back quantum computing?
  67. When will quantum computing finally take off for practical applications?
  68. Quantum cryptography and post-quantum cryptography
  69. QIST — Quantum information science and technology
  70. Experimentation and prototyping vs. development and production
  71. Quantum computer science
  72. Quantum software engineering
  73. Standardization
  74. Education and training
  75. History
  76. Quantum information science is a misnomer
  77. Glossary
  78. What’s next?
  • The term “quantum information science” means the use of the laws of quantum physics for the storage, transmission, manipulation, computing, or measurement of information.
  1. Quantum computing offers much greater performance than classical computing through quantum parallelism which offers an exponential speedup — evaluating many (all) possibilities in parallel, in a single calculation.
  2. Quantum communication offers inherent security through quantum entanglement — also known as spooky action at a distance, in contrast to security as a problematic afterthought for classical communication and networking.
  3. Quantum metrology and quantum sensing offer much greater accuracy and precision for measurements of physical quantities and detection of objects.
  • Physics — especially quantum mechanics
  • Physical science — anything relying on quantum effects, such as chemistry
  • Materials science
  • Materials engineering
  • Mathematics
  • Computer science
  • Software development
  • Software engineering — in theory, eventually
  • Applications development
  • Electrical engineering
  • Computer engineering
  • Mechanical engineering
  1. Discrete rather than continuous values for physical quantities.
  2. Quanta for discrete values. The unit for discrete values. Technically, quantum is a singular unit and quanta is the plural of quantum (just as with data and datum.)
  3. Particle and wave duality. Particles have wave properties and behavior, and waves have particle properties and behavior. For example, a photon can act as a particle as well as a wave, and an electron can act as a wave as well as a particle.
  4. Probabilistic rather than strictly deterministic behavior.
  5. Uncertainty of exact value or measurement. More than just uncertainty of any measurement, there is uncertainty in the actual value of any property, as a fundamental principle of quantum mechanics. A given property of a given quantum system may have a range of values, even before the property is measured. For example, a particle or wave can be at two — or more — positions at the same moment of time.
  6. Superposition of states — can be in two states at the same time.
  7. Entanglement — the same quantum state can exist at two physically separated locations at the same time.
  8. Spooky action at a distance — popular reference to entanglement.
  9. Phase — the complex or imaginary part of the probability amplitude of a quantum state. The notion of cyclical or periodic behavior or a fraction of a single cycle of a wave or circle. Measured either in radians (two pi radians in a circle or cycle) or a fraction between 0.0 and 1.0, where 1.0 corresponds to a full, single cycle or circle (two pi radians.)
  10. Interference — cancellation or reinforcement of the complex or imaginary part of the probability amplitude of two quantum states (phases). Useful for quantum computing — it enables quantum parallelism. Not to be confused with environmental interference which disrupts the operation of a quantum system.
  11. Wave function is used to fully describe the state of a particle or wave (technically, an isolated quantum system) based on the probabilities of superposed and entangled states. The sum of the basis states of the quantum system, each weighted by its probability amplitude. Linear algebra is the notation used to express a wave function.
  12. Probability amplitude — a complex number with both real and imaginary parts. Square it and then take the square root to get the probability for a particular basis state.
  13. Basis state — the actual numeric value of a single quantum state, comparable to a binary 0 or 1.
  14. Computational basis state — the combined basis states of a collection of qubits. A collection of strings of 0’s and 1’s, each string having a probability amplitude as its weight in the wave function. Essentially each string is an n-bit binary value.
  15. Quantum state — the state of an isolated quantum system described by its wave function. Alternatively, a single basis state.
  16. Collapse of wave function on measurement, where the probabilities of superposed states will influence but not completely determine the observed value. Measurement always causes the wave function of a quantum system to collapse.
  17. Measurement — the process of observing a quantum system. By definition, measurement causes collapse of the wave function, and will always produce a single basis state (0 or 1) or computational basis state (string of 0’s and 1’s) regardless of any superposition or entanglement which may be defined by the wave function of the quantum system.
  18. Tunneling — the ability of a subatomic particle or wave such as an electron to appear to be able to move through a solid barrier as if it weren’t there. In actuality, quantum mechanics dictates that a particle or wave has a probability to be at any given location, so that a particle or wave can have a probability of being at either side of the barrier at a given moment, allowing the particle or wave to appear to skip over or through the barrier in the next moment. An example would be electrons and a Josephson junction used in a superconducting transmon qubit.
  1. The quantum state is described by a wave function.
  2. The individual possible states are known as basis states. Such as a 0 and a 1.
  3. Each basis state in a wave function occurs with some probability.
  4. A basis state can also have a complex or imaginary component, known as a phase, which is periodic or cyclical. This is exploited in quantum computing to enable quantum parallelism using interference of the phase of a potentially large number of quantum states.
  5. The probability and phase are combined into a single, complex value, called the probability amplitude, where the probability is the square root of the absolute value (or modulus) of the complex number.
  6. The basis states and their probability amplitudes are combined to form the wave function.
  7. If the probability of a basis state is other than 0.0 or 1.0, the two basis states are superposed.
  8. The quantum states of two separate particles or waves — two isolated quantum systems — can be shared or entangled.
  1. Time
  2. Distance
  3. Acceleration
  4. Momentum
  5. Angular velocity
  6. Mass
  7. Energy
  8. Electromagnetic radiation — frequency, intensity
  9. Gas concentration
  10. Magnetic fields
  11. Electric fields, charge
  12. Temperature
  13. Pressure
  14. Gravity, gravity waves
  1. The desired quantum computer is not readily available due to scheduling, demand, or cost.
  2. It is not yet practical to design and build the desired quantum computer.
  3. Debugging of quantum programs is needed, which is not possible on a real physical quantum computer.
  4. An audit log of the operations of a quantum program are needed, which is not possible on a real physical quantum computer.
  5. It is desirable to do many runs of a quantum program during development and testing, without the overhead of gaining access to a real physical quantum computer for each run.
  1. An electronic component.
  2. A computer.
  3. A digital electronic component such as a gate or flip flop.
  4. A quantum computer. Such as a so-called NISQ device.
  5. A qubit.
  6. A sensor.
  7. A quantum sensor.
  1. Quantum physics.
  2. Quantum chemistry. Known also as quantum computational chemistry.
  3. Quantum biology. Any process which involves chemical reactions and the exchange or transfer of energy.
  1. Experimentation. Staff are simply familiarizing themselves with the new technology, software, and tools. Staff may actually be using the new technology, but not for actual production deployment — or anything even close.
  2. Prototyping and mockups. Staff are doing preliminary implementations of capabilities to see how well they work, how users respond to them, and what issues crop up, but nothing suitable for production.
  3. Development. Having identified all issues and having come up with proposed solutions, staff is now executing the engineering tasks needed to develop full-scale, production-ready solutions. Including testing, well before actual deployment.
  4. Deployment and production. The development of solutions has been completed, but rolling solutions out to users, testing with real users, training users on the new technology, and transitioning from existing solutions to the new solutions can be a tedious, difficult, and time-consuming array of tasks. Parallel use of the old and the new solutions may be necessary for an extended period until the new solutions have proved themselves in the full range of production scenarios, including peak periods and outages which could impact the new solutions.


Over time, de jure standardization (formal standards) for quantum information science and its subfields will become more common, more formal, and more rigorous, but for now, the field is too dynamic and changing too rapidly for de jure standardization to have much appeal or traction.

Education and training

This paper won’t delve deeply into education and training for quantum information science, but simply provide a high-level view. Education and training are essential, for any new field of any significant complexity.

  1. Both formal education and informal education, which is sometimes referred to as simply training.
  2. Undergraduate. Both minor and major in quantum information science or one or more of its subfields, especially quantum computing.
  3. Graduate. Both focus on quantum information science or one or more of its subfields, especially quantum computing, and some degree of exposure to quantum information science for degrees in other fields.
  4. PhD. Same as for graduate, but with a greater degree of specialization.
  5. Certificate programs for professionals who already have degrees, but not in quantum information science. May range from one-month to six-week to one-year programs. May include summer programs and summer schools.
  6. Seminars and boot camps on various aspects of quantum information science. May range from one hour to half a day, two days, three days, to a full week, or maybe two.
  7. On-the-job training. By the employer, possibly outsourced.
  8. Vender-specific training.
  9. Lifelong learning. The field is evolving rapidly and continuously, so there is literally no end to either education or training.
  10. Retraining of displaced workers.
  11. High school. Exposure to basic quantum information science concepts in math, science, and computer science or other STEM courses, including some hands-on use.
  12. Interdisciplinary. Especially for applications in areas where technical expertise is not as deep as required for quantum information science.


For historical reference, a workshop on quantum information science was held by the National Science Foundation (NSF) over twenty years ago, on October 28–29, 1999 in Arlington, Virginia:

  • Quantum information science (QIS) is a new field of science and technology, combining and drawing on the disciplines of physical science, mathematics, computer science, and engineering. Its aim is to understand how certain fundamental laws of physics discovered earlier in this century can be harnessed to dramatically improve the acquisition, transmission, and processing of information. The exciting scientific opportunities offered by QIS are attracting the interest of a growing community of scientists and technologists, and are promoting unprecedented interactions across traditional disciplinary boundaries. Advances in QIS will become increasingly critical to our national competitiveness in information technology during the coming century.
  • The information technology revolution of the past several decades has been driven by steady advances in the miniaturization of electronic circuitry on silicon chips, allowing performance to double roughly every 18 months (“Moore’s law”). But in fewer than 20 years, this shrinkage will reach atomic dimensions, necessitating a new paradigm if progress is to continue at anything like the rate we have become used to. Accordingly, considerable thought and long-range planning are already being devoted to the challenges of designing and fabricating devices at the atomic scale and getting them to work reliably, a field broadly known as nanotechnology.
  • However, it has long been known that atoms and other tiny objects obey laws of quantum physics that in many respects defy common sense. For example, observing an atom disturbs its motion, while not observing it causes it to spread out and behave as if it were in several different places at the same time. Until about five years ago, such quantum effects have mostly been seen as a nuisance, causing small devices to be less reliable and more error-prone than their larger cousins.
  • What is new, and what makes QIS a single coherent field despite spanning several traditional disciplines, is the realization that quantum effects are not just a nuisance, but in fact can be exploited to perform important and otherwise impossible information-processing tasks. Already quantum effects have been used to create unbreakable codes, and a quantum computer, if one can be built in the future, could easily perform some computations that would take longer than the age of the universe on today’s supercomputers. The way in which quantum effects speed up computation is not a simple quantitative improvement, like solving a hard problem more quickly by using a faster processor or many processors working in parallel. Rather it is a qualitative improvement, like the improvement one gets from calculating with decimal instead of Roman numerals. For the first time, the physical form of information has a qualitative rather than merely a quantitative bearing on how efficiently the information can be processed, and the things that can be done with it.
  • The term “quantum information science” means the use of the laws of quantum physics for the storage, transmission, manipulation, computing, or measurement of information.

Quantum information science is a misnomer

Quantum information science is a misnomer on many levels.

  1. Science and engineering are usually treated separately in the classical world, but are merged in quantum information science. The hardware engineering of quantum devices is included under quantum information science.
  2. In the classical world, electrical engineering and computer engineering are treated as separate from computer science, while in the quantum world the notion of engineering is subsumed under science — under quantum information science, that is.
  3. There is no quantum computer science as a direct analog to the computer science of the classical world. Any notion of quantum computer science is nebulously covered under the broad umbrella of quantum computing, which includes hardware, unlike the classical world where computer engineering is considered a specialized field of engineering rather than being covered by computer science.
  4. Quantum information science suggests a strong parallel with classical information science, but that is far from true. Information science classically is about information alone in an abstract sense, divorced from hardware and the physical means by which information is represented and transmitted. But quantum information science includes the hardware and physical aspects of capturing, storing, organizing, accessing, analyzing, manipulating, and communicating information. As of this moment there is no accepted umbrella term under quantum information science that serves as the analog to classical information science.
  5. All of quantum computing is included under quantum information science, while the vast bulk of classical computing is NOT included under classical information science.
  6. Quantum communication is covered by quantum information science, whereas the physical aspects of communication are covered under engineering and information theory in the classical world. Quantum information theory, the direct analog of classical information theory (ala Claude Shannon) is covered by quantum information science, while classical information theory is NOT considered part of information science in the classical world.
  7. All of quantum metrology and quantum sensing are covered by quantum information science, and while portions are indeed under science (physics) in the classical world, a substantial fraction belongs more properly under engineering.
  8. Quantum information is an ill-defined, vague, and ambiguous term. Granted, I do offer my own, clear definition in this paper, but my definition is not binding on others, and in fact is not fully representative of current usage by others. Sure, quantum information is the quantum analog of information in the classical world, but that is too vague. Does it refer to qubits, alone? Unclear. Does it refer to quantum state, alone? Again, unclear. Does it refer to superposition and entanglement of qubits, alone? Does it refer to wave functions, alone? Still unclear. Does it refer to basis states, alone? No clarity. And what about phase (imaginary part of probability amplitude)? No clarity. Does it refer to computational basis states, alone? No clarity at all. Is quantum information discrete as in the classical world, or continuous (rotations of the three-dimensional Bloch sphere)? So confusing. Given superposition and entanglement, is there actually a unit of quantum information? Not so clear. And then there are qutrits and qudits as well. And then photonic quantum computing introduces are qumodes. And squeezed states. Some combination of all of the above? Okay, sure, I guess, but that hardly seems like a sound basis for something worthy of being called a science.
  9. The hardware devices for holding, storing, and manipulating quantum informationqubits — are fully covered by quantum information science, while the hardware devices for holding, storing, and manipulating classical information — flip flops, logic gates, memory cells, and storage media — are NOT considered under classical information science, since they are covered by electrical engineering and computer engineering.
  10. There’s no notion of software engineering (or quantum software engineering) included under quantum information science. You could argue that it is or should be under quantum computing, but that belies its significance and importance.
  11. There is no notion of whether applications are included under quantum information science, or whether quantum information science is simply the raw underlying technology, the platform, and applications are built on top of quantum information science. Again, clarity is needed.
  12. Numerous entities refer to quantum information science and technology as if there are some aspects which are not considered directly under the main umbrella of quantum information science. I surmise that some writers are excluding applications and commercial products and services, trying to treat quantum information science as more of an R&D research effort. For example, the National Quantum Initiative Act of Congress: “The purpose of this Act is to ensure the continued leadership of the United States in quantum information science and its technology applications by… supporting research, development, demonstration, and application of quantum information science and technology…”. And, USC: “Quantum information science and technology is an emerging interdisciplinary academic discipline concerned with the study of the new possibilities quantum mechanics offers for the acquisition, transmission, and processing of information.” And, Japan: “we have witnessed the growing interest and rapid progress of quantum information science and technology around the world. In Japan, the early basic research in this field has mainly been supported by a unique program…” And, Berkeley: “CS C191. Quantum Information Science and Technology… This multidisciplinary course provides an introduction to fundamental conceptual aspects of quantum mechanics from a computational and informational theoretic perspective, as well as physical implementations and technological applications of quantum information science.” And, the White House: “The SCQIS assesses the national portfolio using seven broad categories: four in fundamental science (S1-S4) and three in technological development (T1-T3). … These seven areas represent the broad foundation necessary to support a full industrial and Governmental effort in quantum information science and technology.” And, University of Illinois Urbana-Champaign: “Illinois Quantum Information Science and Technology Center”. And, Princeton: “The initiative comes at a time of national momentum for quantum sciences at the University, government and industry level. In 2018, the federal government established the National Quantum Initiative to energize research and training in quantum information science and technology.” And, Los Alamos National Laboratory: “This roadmap has been formulated and written by the members of a Technology Experts Panel… whose membership of internationally recognized researchers … in quantum information science and technology (QIST) held a kick-off meeting…” And, University of Cologne: “In the scope of the Cluster of Excellence “ML4Q”, courses in Bonn and Cologne from the following list can be taken to be acknowledged in the area of “Quantum Information Science and Technology”.” And, National Academies of Sciences, Engineering, and Medicine: “Foundations of Quantum Information Science and Technology”. Just to mention a few.
  13. It is ambiguous whether quantum applications are included under quantum information science, or more properly belong under QIST — quantum information science and technology, unlike classical computer science which does NOT include applications.


My own glossary of quantum computing terms includes many of the terms related to the other subfields of quantum information science as well:

What’s next?

More work is needed:

  1. Next level of detail for quantum computing — but still at a reasonably high level.
  2. Next level of detail for quantum communication — but still at a reasonably high level.
  3. Next level of detail for quantum metrology and quantum sensing — but still at a reasonably high level.
  4. Define personas, use cases, and access patterns for quantum information science overall, and for quantum computing, quantum communication, and quantum metrology and quantum sensing in particular.
  5. Vast amounts of research and technology development in all three subfields of quantum information science.



Freelance Consultant

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