The field of quantum technologies is comprised of quantum communication, quantum simulation, quantum computation, quantum sensing and metrology. Technologies are being developed that address individual quantum states and use quantum properties such as superposition and entanglement. This cluster of topics relate to quantum technology applications outside of quantum computing. Quantum technology is expected to have applications in personalized medicine, natural resource exploration, environmental monitoring and secure communications. For topics specific to quantum computing topics please see Cluster: Quantum Computing.

## Quantum Technology Basics

The following are common and/or foundational terms and concepts related to quantum technology.

- Bell's Theorem
- Coherence
- Integrated quantum photonics
- Loop quantum gravity
- Nanolaser
- Quantum actuator
- Quantum algorithm
- Quantum entanglement
- Quantum field theory (QFT)
- Quantum gravity
- Quantum key distribution
- Quantum mechanics
- Quantum photonics
- Quantum random number generator
- Quantum simulator
- Quantum superposition
- qubits
- Richard Feynman

## Quantum technology materials and fabrication

Quantum technologies utilize quantum superposition and entanglement. Only certain materials allow these fragile quantum phenomena to last long enough or be sufficiently controllable to be useful for encoding or processing information. The following materials are of interest in quantum technology because they allow electron spin to be manipulated and measured.

- Diamonds with nitrogen-vacancy (NV) centers, also called nitrogen-vacancy (NV) color centers
- Diamond metalens
- Graphene
- hexagonal boron nitride
- materials modified by doping
- materials with point defects
- Silicon: linking spin qubits associated with luminescent defects in silicon with photon qubits
- Twistronics
- Two-dimensional (2D) materials

### Filters for superconducting quantum circuits

Superconducting quantum circuits are sensitive to electromagnetic interference and thermal radiation, leading to quantum decoherence, an undesirable phenomenon. The following materials are of interest as filters because they decrease coherence times and are compact.

- carbon nanotubes in a lossy transmission line filter

### Quantum dots

Quantum dots (QDs) are semiconducting nanocrystals lacking toxic heavy metals. QDs are efficient light emitters that may be used in displays, solar cells and light-emitting diodes. The small size of quantum dots is about 1-100 nanometers and they are composed of a core and shell or multiple shell layers.

- Cadmium selenide , found in LED and other lighting applications
- cadmium telluride
- colloidal quantum dots
- DNA-functionalized quantum dots
- electron beam lithography
- gallium arsenide

- InP/ZnSe/ZnS quantum dot light-emitting diodes
- Luminescent quantum dots (LQDs)
- Molecular beam epitaxy
- II-V-semiconductors: made of elements of main group III of the periodic table (boron, aluminium, gallium, indium) and main group V (nitrogen, phosphorus, arsenic, antimony, bismuth)
- II-VI- semiconductors: made of elements of transition metal group II (zinc, cadmium) and main group VI (oxygen, sulphur, selenium, tellurium)
- semiconductor quantum dots
- Silicon (SiQDs)
- Zinc oxide

## Quantum communication and cryptography

In communication, transmittance of information such as data or video calls can be packaged and secured using quantum methods. Quantum communication generates and uses quantum states and resources for communication protocols with applications in secure communication, long-term secure storage, cloud computing and other cryptography-related tasks. Quantum communication also applies to a secure future ‘quantum web’ involving quantum resources like entanglement, nonlocality, randomness and connecting remote devices and systems. Typically, protocols are built on quantum random number generators (QRNG) for secret keys and quantum key distribution (QKD) for their secure distribution.

- cryptography
- Device-independent quantum cryptography
- Device-independent quantum key distribution
- quantum cryptography
- Quantum encryption
- Quantum key distribution
- Quantum resistant ledger
- Three-stage quantum cryptography protocol

## Quantum optics

Quantum optics is the study of the quantum properties of light. Quantum technologies as a scientific field came from quantum optics, which provided the tools to study the foundations of quantum mechanics with precision. Many ideas were tested through the interaction between an isolated atom and a light field. Quantum optics combined fundamental physics with applications to technology. As a candidate to implement quantum technology photons have the advantage of not requiring cryogenic temperatures and the environment does not affect them very much. They do require precise alignment of an optical setup.

- Atom optics: A branch of quantum optics that aims to use quantum coherences of atomic motion with applications in sensors, accelerometers and atomic clocks
- Cavity quantum electrodynamics (cavity QED)
- Gaussian states
- Integrated photonic circuits (photonic chips or photonic integrated circuits)
- Integrated quantum photonics
- The Jaynes–Cummings model (JCM)
- Quantisation of energy
- Quantum photonics
- Photon
- Sir Peter Knight
- Spontaneous parametric down-conversion (also known as SPDC, parametric fluorescence or parametric scattering)
- Squeezed state of light

## Quantum sensors and measurement

Quantum sensors may be used to measure electric, magnetic or gravitational fields, as well as other properties including temperature, acceleration, rotation or pressure. Gravimeters are a type of quantum sensor that uses cold atoms to measure the strength of gravity and can be used for sensing what is underground with applications in surveying for oil, minerals, monitoring volcanoes and construction. Quantum sensors are also used in diagnostics such as clinical breath analysis and environmental monitoring.

- lidar for self-driving cars
- quantum accelerometer
- quantum cascade laser
- quantum dots
- quantum gravity sensor (gravimeter) or cold atom gravity sensor
- Quantum-logic clock (NIST)
- Magnetic Resonance Imaging (MRI)
- rubidium
- Strontium clock (NIST)
- superconducting quantum interference device (SQUID)

## Imaging

Cameras that detect single photons efficiently are able to “see” around corners by using laser pulses which scatter and bounce off objects and re-enter the camera’s field of view. Images are then built up indirectly based on the returning photon patterns.

- Entanglement-enhanced microscope
- Ghost imaging

## Companies

## Quantum photonics

### Research groups and initiatives

- The Cold Atom Laboratory (CAL)
- The Gravity Pioneer project (UK consortium of scientific and engineering companies and university researchers)
- InfiniQuant
- MEXT Q-LEAP (Japan)
- NASA
- National Innovation and Science Agenda (Australia)
- The National Quantum Initiative (NQI) (USA)
- NIST Post-Quantum Cryptography Standardization project
- Quantum sensors group (NIST)
- The Quantum Technologies Flagship (European Union)
- Russian Quantum Center
- Transformative Quantum Technologies (TQT) - University of Waterloo

## Investment

- Lux Capital
- Quantonation
- QuantumX
- Pascal Capital

## Timeline

## People

## Further reading

The quantum technologies roadmap: a European community view

Antonio Acín, Immanuel Bloch, Harry Buhrman, Tommaso Calarco, Christopher Eichler, Jens Eisert, Daniel Esteve, Nicolas Gisin, Steffen J Glaser, Fedor Jelezko, Stefan Kuhr, Maciej Lewenstein, Max F Riedel, Piet O Schmidt, Rob Thew, Andreas Wallraff, Ian Walmsley, Frank K Wilhelm

Journal