quantum photonics (original) (raw)

Definition: the science and technology using quantum optics for applications like quantum communications, quantum computing and quantum metrology

Categories: photonic devices, quantum photonics

• photonics
  • silicon photonics
  • quantum photonics
    * quantum communications
    * quantum information processing
    * quantum cryptography
    * quantum key distribution
    * quantum computing
    * quantum simulation
    * quantum sensing
    * quantum lithography
  • quantum electronics
  • space photonics
  • astrophotonics

Related: photonicsquantum opticsphotonsquantum information processingquantum cryptographyquantum key distributionsingle-photon sourcesquantum light sourceslasers for quantum photonics

Page views in 12 months: 997

DOI: 10.61835/9qk Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn

Content quality and neutrality are maintained according to our editorial policy.

📦 For purchasing quantum computers, use the RP Photonics Buyer's Guide — an expert-curated directory for finding all relevant suppliers, which also offers advanced purchasing assistance.

Contents

What is Quantum Photonics?

Quantum Information Processing

Applications of Quantum Photonics

Quantum Communications

Quantum Computing

Quantum Simulation

Quantum Sensing

Quantum Lithography

Technical Aspects

Key Devices and Functions

Integrated Quantum Photonics

Levels of Maturity

Frequently Asked Questions

Summary:

This article provides an overview of quantum photonics, the field leveraging principles from photonics and quantum optics for technological applications. It explains the fundamentals of quantum information processing, where qubits and entanglement are used to perform computations via quantum gates.

Key applications are detailed, including secure quantum communication via quantum key distribution, high-speed quantum computing, the simulation of complex quantum systems, and ultra-sensitive quantum sensing that can surpass the standard quantum limit.

The text also covers the essential hardware, such as single-photon sources, specialized lasers, and detectors, highlighting the crucial role of light-matter interactions and the trend towards miniaturization with integrated quantum photonics.

(This summary was generated with AI based on the article content and has been reviewed by the article’s author.)

What is Quantum Photonics?

Quantum photonics is a branch of science and technology that harnesses the principles of photonics and specifically of quantum optics to enable applications where quantum phenomena play a crucial role. The term quantum photonics is mostly used in the context of technological applications rather than pure fundamental research; it may also be called applied quantum optics.

Quantum Information Processing

In different fields of application, quantum photonics involves techniques of quantum information processing:

• Generally, qubits (bits of quantum information) are represented by superpositions of quantum states, with quantum entanglement often playing a crucial role.
• Based on some inputs, one usually starts with generating suitable quantum states carrying quantum information.
• One then exploits the evolution of such states, e.g. by sending photons through optical elements like beam splitters and waveplates, and using interactions of photon quantum states in interferometers. Such operations can implement quantum gates, which process one or more qubits much like classical logic gates process bits in conventional computers. For example, quantum gates can perform quantum bit flips and rotations, or generate entanglement between qubits.
• After some coherent evolution of qubits, quantum states are often projected via measurements, e.g. by detecting photons destructively.

See the article on quantum information processing.

Applications of Quantum Photonics

Quantum Communications

Quantum communication utilizes quantum effects to transmit information with strong security guarantees. Techniques such as quantum key distribution leverage quantum principles such as the no-cloning theorem to prevent undetected eavesdropping. Other notable methods include quantum teleportation (which also finds use in quantum computing), for example for quantum repeaters: While classical optical telecom signals can be sent through erbium-doped fiber amplifiers, for example, the preservation of quantum states requires more sophisticated technology based on quantum entanglement. Generally, one utilizes various methods of quantum information processing (see above).

See the articles on quantum cryptography and quantum key distribution.

Quantum Computing

In quantum computing, one encodes information with quantum bits, in short qubits, as linear superpositions between two states of a single quantum object, for example of a photon or an atom. Sometimes, quantum information is represented by quantum-entangled states of multiple quantum objects. In contrast, a classical bit can always be only in one of the two states, not in a superposition.

If a combination of ($N$) qubits is used, that can be in a superposition of ($2^N$) states. The coherent evolution of such qubits under well controlled conditions depends on all involved quantum states and can thus be used to perform certain operations with far higher speed than is possible with classical computers. For example, it should be possible to efficiently perform certain operations like prime factorization; that would allow one to crack current cryptography systems which would appear to be completely safe against the use of conventional (classical) technologies. Quantum computing includes both digital realizations, such as quantum logic gates and measurements, and analog approaches, such as quantum simulation, annealing, or adiabatic quantum computing.

Photonics is considered a promising platform alongside alternative technologies such as superconducting circuits.

Quantum Simulation

Quantum simulation is the use of quantum systems — either digital quantum computers or specialized analog devices — to model and analyze the behavior of complex quantum phenomena, which are often intractable for classical computers. This capability leverages key quantum principles such as superposition, entanglement, and quantum interference.

Many natural and engineered systems follow the laws of quantum mechanics, including molecules, materials, condensed matter systems, atomic nuclei, and high-energy physics phenomena. As these systems grow in size, the number of possible quantum states increases exponentially, and essentially this is why the capabilities of classical computers for exact simulations are rapidly overwhelmed.

Richard Feynman famously proposed that the best way to simulate quantum systems is with quantum hardware itself. Here, the quantum system used for simulation may be of very different nature from that to be simulated; yet, it may well capture the essential structure of a quantum problem, and may be far more convenient concerning practical implementation.

Quantum simulations are also made with software tools running on classical processors, but these can only emulate quantum algorithms for small quantum systems. They can be useful for prototyping, testing and debugging quantum algorithms, but are limited by exponential memory requirements to a few dozen qubits.

Quantum Sensing

Various types of measurements are fundamentally limited in sensitivity by quantum effects. Traditional technical approaches e.g. in interferometry often do not reach the fundamental quantum-mechanical limits, but are rather stuck at the standard quantum limit (SQL).

Quantum sensing aims to overcome these constraints by actively manipulating quantum states and utilizing effects such as entanglement, superposition, and quantum correlations.

A prominent example is the use of squeezed states of light, where quantum noise in one observable (e.g., optical phase) is reduced below the SQL at the expense of increased noise in the conjugate variable (e.g., amplitude). When these states are injected into interferometers, the phase measurement sensitivity can be enhanced — enabling the detection of extremely weak signals that would be obscured by quantum noise in conventional systems. The practical impact of quantum sensing is particularly evident in advanced gravitational wave detectors, such as LIGO and Virgo, where squeezed light has enabled unprecedented sensitivity to extremely weak spacetime distortions.

Beyond gravitational wave astronomy, quantum sensing methods are being developed and applied in various other fields:

• Ultra-precise optical clocks can reach further performance advances utilizing quantum techniques. For example, one considers using many-body entangled states of large ensembles of atoms in an optical clock, and the use of squeezed light for preparing spin-squeezed atoms.
• Magnetometry can utilize quantum correlations to map ultra-weak magnetic fields.
• In some medical imaging and spectroscopy techniques, enhanced performance can be achieved with quantum strategies.
• Force and displacement sensors, reaching into domains limited only by fundamental quantum mechanics, may also be improved.

Quantum Lithography

The spatial resolution of optical lithography is normally limited by diffraction to about half the optical wavelength. The traditional way of improving resolution is thus essentially to use shorter and shorter wavelengths — already in the extreme ultraviolet (EUV) region.

Quantum lithography is an emerging area investigating how quantum techniques could enable substantial quantum-superresolution beyond the classical diffraction barrier. In principle, using entangled ($N$)-photon quantum states (such as NOON states), one could achieve a theoretical resolution of approximately ($\lambda/2N$). Realizing this improvement, however, presents significant challenges: It requires the development of bright, well-controlled quantum light sources with suitable properties, and of photoresists engineered for multiphoton absorption (remaining insensitive to single-photon or lower-order absorption processes). Moreover, practical applications would necessitate the ability to generate arbitrary, complex two-dimensional patterns — not just simple lines or spots.

Technical Aspects

Quantum photonics involves the generation, manipulation, and detection of light, frequently using single photons. Interactions between light and matter — such as those between photons and atoms or ions trapped in optical potentials, or between photons and quantum dots — are often essential for processing quantum information. Photons, relative to atoms or ions, are less susceptible to decoherence from external fields and are readily manipulated, though interactions with matter remain vital for certain quantum tasks.

Key Devices and Functions

Some critical devices for quantum photonics are:

• Single-photon sources are a kind of quantum light sources that can reliably produce individual photons on demand. They are essential for quantum communication and computing.
• Photon pair sources generate pairs of photons, i.e., with linked quantum states. The photon states can be entangled.
• Various kinds of lasers are required, often with special performance specifications, for example with ultra-low laser noise and tailored emission wavelengths.
• Single-photon detectors can register single photons, e.g. for photon counting. Some types of photodetectors can resolve photon numbers. Detectors are important for measuring quantum states and for quantum key distribution in quantum cryptography. A crucial quality in that context is a very high quantum efficiency.
• Photons can be made to interact with single atoms or ions, or with quantum dots, which are somewhat similar to atoms or ions in terms of their excited levels. Such interactions may be used to manipulate quantum information.
• Some types of optical resonators (some micro- or nano-resonators on photonic integrated circuits) are suitable for storing photons for a certain period, also for enhancing light-matter interactions. They may thus be used for controlling and manipulating quantum states.
• Various nonlinear materials can be utilized, for example for generating photon pairs or squeezed states of light.
• Many other types of components are also utilized, although not being specific for quantum photonics; examples are waveguides including optical fibers, beam splitters and dichroic mirrors.

Integrated Quantum Photonics

While fundamental experiments often employ large-scale setups of bulk components, the realization of practical quantum photonic technologies will depend on developing miniaturized solutions: photonic integrated circuits that process quantum information in a compact and scalable form. Achieving high-fidelity on-chip sources of single and entangled photons, robust quantum gates and low-loss propagation presents substantial technical challenges.

Levels of Maturity

Some areas of quantum photonics, especially quantum communication (notably quantum cryptography), have already seen real-world deployment in early stages — for example, with banks starting to utilize quantum-secure information transfer. Other sectors, such as photonic quantum computing, remain active topics of investigation, with significant advances but uncertain timelines for the realization of large-scale, practical quantum computers. Progress is rapid, but it is hard to anticipate how and when powerful photonic quantum computers will be built.

Frequently Asked Questions

This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).

What is quantum photonics?

Quantum photonics is a field of science and technology that uses the principles of photonics and quantum optics for applications where quantum phenomena are essential. It is often considered to be applied quantum optics.

What are the main applications of quantum photonics?

Key applications include quantum communication for secure data transfer, quantum computing for solving complex problems, quantum simulation of physical systems, and quantum sensing for highly precise measurements.

How does quantum communication improve security?

It utilizes techniques such as quantum key distribution (QKD), which leverages quantum principles like the no-cloning theorem to make undetected eavesdropping impossible.

What is the goal of quantum sensing?

Quantum sensing aims to overcome the standard quantum limit (SQL) in measurement sensitivity by using quantum effects like entanglement and squeezed states of light, enabling the detection of extremely weak signals.

What key devices are used in quantum photonics?

Why is integrated quantum photonics important?

For practical applications, quantum technologies need to be miniaturized and scalable. Photonic integrated circuits provide a platform to process quantum information in a compact and robust form.

Bibliography

(Suggest additional literature!)

Questions and Comments from Users

Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.

Please do not enter personal data here. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him, e.g. via e-mail.

By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.