User:Manonpbart/Quantum sensor

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The field of quantum sensing deals with the design and engineering of quantum sources (e.g., entangled) and quantum measurements that are able to beat the performance of classical strategies in a number of technological applications. This can be done with photonic systems or non-photonic systems such as solid state systems.

Quantum sensing utilizes properties of quantum mechanics, such as quantum entanglement, interference and quantum state squeezing, that have optimized precision and beat current limits in sensor technology and evade the Heisenberg uncertainty principle.

''Photonic quantum sensing leverages entanglement, single photons and squeezed states to perform extremely precise measurements. Optical sensing makes use of continuous variable quantum systems such as different degrees of freedom of the electromagnetic field, vibrational modes of solids, and Bose-Einstein condensates. These quantum systems can be probed to characterize an unknown transformation between two quantum states. Several methods are in place to improve photonic sensors such quantum illumination of targets which has been used to improve detection of weak signals by the use of quantum correlation. ''

In photonics and quantum optics, quantum sensors are often built on continuous variable systems, i.e., quantum systems characterized by continuous degrees of freedom such as position and momentum quadratures. The basic working mechanism typically relies on  using  optical states of light, which have often involving quantum mechanical properties such as squeezing or two-mode entanglement. These states are particularly sensitive to record physical transformations that are finally detected by interferometric measurements.

Quantum sensing can also be utilized in non-photonic areas such as spin qubits, trapped ions, and flux qubits. These systems can be compared by physical characteristics to which they respond, for example, trapped ions respond to electrical fields while spin systems will respond to magnetic fields. ''Trapped Ions are useful in their quantized motional levels which are strongly coupled to the electric field. They have been proposed to study electric field noise above surfaces, and more recently, rotation sensors. ''

In solid-state physics, a quantum sensor is a quantum device that responds to a stimulus. Usually this refers to a sensor which has quantized energy levels, uses quantum coherence to measure a physical quantity, or uses entanglement to improve measurements beyond what can be done with classical sensors. There are 4 criteria for solid-state quantum sensors:
 * 1) The system has to have discrete, resolvable energy levels.
 * 2) You can initialize the sensor and you can perform readout (turn on and get answer).
 * 3) You can coherently manipulate the sensor.
 * 4) The sensor interacts with a physical quantity and has some response to that quantity.

Ongoing Research and Applications
Quantum Sensors have applications in a wide variety of fields including microscopy, positioning systems, communication technology, electric and magnetic field sensors, as well as geophysical areas of research such as mineral prospecting and seismology. Many measurement devices utilize quantum properties in order to probe measurements such as atomic clocks, superconducting quantum interference devices, and nuclear magnetic resonance spectroscopy. With new technological advancements, individual quantum systems can be used as measurement devices, utilizing entanglement, superposition, interference and squeezing to enhance sensitivity and surpass performance of classical strategies.

The Defense Advanced Research Projects Agency (DARPA) launched a research program in optical quantum sensors that seeks to exploit ideas from quantum metrology and quantum imaging, such as quantum lithography and the NOON state, in order to achieve these goals with optical sensor systems such as lidar.

''For photonic systems, other current areas of research consider feedback and adaptive protocols. This is an active area of research in discrimination and estimation of bosonic loss. ''

Quantum sensor is also a term used in other settings where entangled quantum systems are exploited to make better atomic clocks or more sensitive magnetometers.

A good example of an early quantum sensor is an APD avalanche photodiode ''(ADP). APDs have been used to detect entangled photons.and in fact With additional cooling and sensor improvements, APDs can be used where in place of PMTs, in fields such as once ruled the market such as'' medical imaging. APDs in the form of 2-D and even 3-D stacked arrays, can be as a direct replacement for conventional sensors based on silicon diodes.

''Injecting squeezed light into interferometers allows for higher sensitivity to weak signals that would be unable to be classically detected. A practical application of quantum sensing is realized in gravitational wave sensing. Gravitational wave detectors, such as LIGO, utilize squeezed light to measure signals below the standard quantum limit . Squeezed light has also been used to detect signals below the standard quantum limit in plasmonic sensors and atomic force microscopy .''

''Quantum sensing also has the capability to overcome resolution limits, where current issues of vanishing distinguishability between two close frequencies can be overcome by making the projection noise vanish. The diminishing projection noise has direct applications in communication protocols and nano-Nuclear Magnetic Resonance. ''

Review by J Hernandez, Research was well done, but there were some grammatical errors here and there. Overall, great organization and structure, very well done.