quantum sensor

In photonics and quantum optics, photonic quantum sensing leverages entanglement, single photons and squeezed states to perform extremely precise measurements. Optical sensing makes use of continuously variable quantum systems such as different degrees of freedom of the electromagnetic field, vibrational modes of solids, and Bose–Einstein condensates.{{Cite journal|last1=Adesso|first1=Gerardo|last2=Ragy|first2=Sammy|last3=Lee|first3=Antony R.|date=June 2014|title=Continuous Variable Quantum Information: Gaussian States and Beyond|journal=Open Systems & Information Dynamics|language=en|volume=21|issue=1n02|pages=1440001|doi=10.1142/S1230161214400010|arxiv=1401.4679|s2cid=15318256}} These quantum systems can be probed to characterize an unknown transformation between two quantum states. Several methods are in place to improve photonic sensors' quantum illumination of targets, which have been used to improve detection of weak signals by the use of quantum correlation.{{cite journal | last1=Gallego Torromé | first1=Ricardo | last2=Barzanjeh | first2=Shabir | title=Advances in quantum radar and quantum LiDAR | journal=Progress in Quantum Electronics | date=2023 | volume=93 | doi=10.1016/j.pquantelec.2023.100497 | page=100497| arxiv=2310.07198 }}{{Cite journal|last1=Tan|first1=Si-Hui|last2=Erkmen|first2=Baris I.|last3=Giovannetti|first3=Vittorio|last4=Guha|first4=Saikat|last5=Lloyd|first5=Seth|last6=Maccone|first6=Lorenzo|last7=Pirandola|first7=Stefano|last8=Shapiro|first8=Jeffrey H.|date=2008-12-18|title=Quantum Illumination with Gaussian States|journal=Physical Review Letters|volume=101|issue=25|pages=253601|doi=10.1103/PhysRevLett.101.253601|pmid=19113706|arxiv=0810.0534|bibcode=2008PhRvL.101y3601T|s2cid=26890855}}{{Cite journal|last1=Shapiro|first1=Jeffrey H|last2=Lloyd|first2=Seth|date=2009-06-24|title=Quantum illumination versus coherent-state target detection|journal=New Journal of Physics|volume=11|issue=6|pages=063045|doi=10.1088/1367-2630/11/6/063045|arxiv=0902.0986|bibcode=2009NJPh...11f3045S|s2cid=2396896}}{{Cite journal|last1=Barzanjeh|first1=Sh.|last2=Abdi|first2=M.|last3=Milburn|first3=G. J.|last4=Tombesi|first4=P.|last5=Vitali|first5=D.|date=2012-09-28|title=Reversible Optical-to-Microwave Quantum Interface|journal=Physical Review Letters|language=en|volume=109|issue=13|pages=130503|doi=10.1103/PhysRevLett.109.130503|pmid=23030075|arxiv=1110.6215|bibcode=2012PhRvL.109m0503B|s2cid=6470118}}{{Cite journal|last1=Guha|first1=Saikat|last2=Erkmen|first2=Baris I.|date=2009-11-10|title=Gaussian-state quantum-illumination receivers for target detection|journal=Physical Review A|language=en|volume=80|issue=5|pages=052310|doi=10.1103/PhysRevA.80.052310|arxiv=0911.0950|bibcode=2009PhRvA..80e2310G|s2cid=109058131}}

Quantum sensors are often built on continuously 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 optical states of light, often involving quantum mechanical properties such as squeezing or two-mode entanglement. These states are sensitive to physical transformations that are detected by interferometric measurements.

Quantum sensing can also be utilized in non-photonic areas such as spin qubits, trapped ions, flux qubits, and nanoparticles.{{Cite journal|last1=Kustura|first1=K.|last2=Gonzalez-Ballestero|first2=C.|last3=De los Ríos Sommer|first3=A.|last4=Meyer|first4=N.|last5=Quidant|first5=R.|last6=Romero-Isart|first6=O.| date=2022-04-07|title=Mechanical Squeezing via Unstable Dynamics in a Microcavity|journal=Physical Review Letters|language=en|volume=128|issue=14|pages=143601|doi=10.1103/PhysRevLett.128.143601|pmid=35476467 |arxiv=2112.01144|bibcode=2022PhRvL.128n3601K |s2cid=244799128 }} 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,{{Cite journal|last1=Brownnutt|first1=M.|last2=Kumph|first2=M.|last3=Rabl|first3=P.|last4=Blatt|first4=R.|date=2015-12-11|title=Ion-trap measurements of electric-field noise near surfaces|journal=Reviews of Modern Physics|language=en|volume=87|issue=4|pages=1419–1482|doi=10.1103/RevModPhys.87.1419|arxiv=1409.6572|bibcode=2015RvMP...87.1419B|s2cid=119008607}} and more recently, rotation sensors.{{Cite journal|last=Campbell|first=W|date=2017-02-23|title=Rotation sensing with trapped ions|journal=Journal of Physics B |volume=50|issue=6|page=064002|doi=10.1088/1361-6455/aa5a8f|arxiv=1609.00659|bibcode=2017JPhB...50f4002C|s2cid=26952809}}

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 or entanglement to improve measurements beyond what can be done with classical sensors. There are four criteria for solid-state quantum sensors:

1. The system has to have discrete, resolvable energy levels.
2. The sensor can be initialized into a well-known state and its state can be read out.
3. The sensor can be coherently manipulated.
4. The sensor interacts with a physical quantity and has some response to that quantity.

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.{{Cite journal|last1=Pezzè|first1=Luca|last2=Smerzi|first2=Augusto|last3=Oberthaler|first3=Markus K.|last4=Schmied|first4=Roman|last5=Treutlein|first5=Philipp|date=2018-09-05|title=Quantum metrology with nonclassical states of atomic ensembles|journal=Reviews of Modern Physics|language=en|volume=90|issue=3|pages=035005|doi=10.1103/RevModPhys.90.035005|arxiv=1609.01609|bibcode=2018RvMP...90c5005P|s2cid=119250709}} 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.

A good example of an early quantum sensor is an avalanche photodiode (APD). APDs have been used to detect entangled photons. With additional cooling and sensor improvements can be used where photomultiplier tubes (PMT) in fields such as medical imaging. APDs, in the form of 2-D and even 3-D stacked arrays, can be used as a direct replacement for conventional sensors based on silicon diodes.{{Cite journal|last=Campbell|first=Joe C.|date=January 2007|title=Recent Advances in Telecommunications Avalanche Photodiodes|journal=Journal of Lightwave Technology|volume=25|issue=1|pages=109–121|doi=10.1109/jlt.2006.888481|bibcode=2007JLwT...25..109C|s2cid=1398387|url=https://zenodo.org/record/896867 }}

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,{{cite journal | doi = 10.1103/PhysRevLett.112.103604 | pmid=24679294 | bibcode=2014PhRvL.112j3604I | volume=112 | issue=10 | pages=103604 | title=Supersensitive Polarization Microscopy Using NOON States of Light | year=2014 | journal=Physical Review Letters | last1 = Israel | first1 = Yonatan}} in order to achieve these goals with optical sensor systems such as lidar. {{cite journal | last1=Gallego Torromé | first1=Ricardo | last2=Barzanjeh | first2=Shabir | title=Advances in quantum radar and quantum LiDAR | journal=Progress in Quantum Electronics | date=2023 | volume=93 | doi=10.1016/j.pquantelec.2023.100497 | page=100497| arxiv=2310.07198 }}[https://www.darpa.mil/sto/space/qsp.html DARPA Quantum Sensor Program].[https://www.fbo.gov/index?id=9bafd20629bf798e1b084fb2582a4b34 BROAD AGENCY ANNOUNCEMENT (BAA) 07-22 Quantum Sensors]{{Cite journal|last1=Zhuang|first1=Quntao|last2=Zhang|first2=Zheshen|last3=Shapiro|first3=Jeffrey H.|date=2017-10-16|title=Entanglement-enhanced lidars for simultaneous range and velocity measurements|journal=Physical Review A|volume=96|issue=4|pages=040304|doi=10.1103/PhysRevA.96.040304|arxiv=1705.06793|bibcode=2017PhRvA..96d0304Z|s2cid=54955615}} The United States judges quantum sensing to be the most mature of quantum technologies for military use, theoretically replacing GPS in areas without coverage or possibly acting with ISR capabilities or detecting submarine or subterranean structures or vehicles, as well as nuclear material.{{cite report |author=Kelley M. Sayler |date=June 7, 2021 |title=Defense Primer: Quantum Technology |url=https://fas.org/sgp/crs/natsec/IF11836.pdf |publisher=Congressional Research Service |access-date=July 22, 2021}}

;Photonic quantum sensors, microscopy and gravitational wave detectors

For photonic systems, current areas of research consider feedback and adaptive protocols. This is an active area of research in discrimination and estimation of bosonic loss.{{Cite journal|last1=Laurenza|first1=Riccardo|last2=Lupo|first2=Cosmo|last3=Spedalieri|first3=Gaetana|last4=Braunstein|first4=Samuel L.|last5=Pirandola|first5=Stefano|date=2018-03-01|title=Channel Simulation in Quantum Metrology|journal=Quantum Measurements and Quantum Metrology|volume=5|issue=1|pages=1–12|doi=10.1515/qmetro-2018-0001|arxiv=1712.06603|bibcode=2018QMQM....5....1L|s2cid=119001470}}

Injecting squeezed light into interferometers allows for higher sensitivity to weak signals that would be unable to be classically detected.{{Cite journal|last1=Li|first1=Dong|last2=Gard|first2=Bryan T.|last3=Gao|first3=Yang|last4=Yuan|first4=Chun-Hua|last5=Zhang|first5=Weiping|last6=Lee|first6=Hwang|last7=Dowling|first7=Jonathan P.|date=2016-12-19|title=Phase sensitivity at the Heisenberg limit in an SU(1,1) interferometer via parity detection|journal=Physical Review A|language=en|volume=94|issue=6|pages=063840|doi=10.1103/PhysRevA.94.063840|arxiv=1603.09019|bibcode=2016PhRvA..94f3840L|s2cid=118404862}} A practical application of quantum sensing is realized in gravitational wave sensing.{{cite book |last1=Barsotti |first1=Lisa |author-link1=Lisa Barsotti|chapter=Quantum Noise Reduction in the LIGO Gravitational Wave Interferometer with Squeezed States of Light |title=CLEO: Applications and Technology 2014 |date=2014 |page=AW3P.4 |doi=10.1364/CLEO_AT.2014.AW3P.4 |isbn=978-1-55752-999-2|s2cid=28876707}} Gravitational wave detectors, such as LIGO, utilize squeezed light to measure signals below the standard quantum limit.{{Cite journal |last1=Yu |first1=Haocun |last2=McCuller |first2=L. |last3=Tse |first3=M. |last4=Kijbunchoo |first4=N. |last5=Barsotti |first5=L. |last6=Mavalvala |first6=N. |date=July 2020|title=Quantum correlations between light and the kilogram-mass mirrors of LIGO|journal=Nature|language=en|volume=583|issue=7814|pages=43–47|doi=10.1038/s41586-020-2420-8|pmid=32612226|arxiv=2002.01519|bibcode=2020Natur.583...43Y|s2cid=211031944}} Squeezed light has also been used to detect signals below the standard quantum limit in plasmonic sensors and atomic force microscopy.{{Cite journal|last1=Pooser|first1=Raphael C.|last2=Lawrie|first2=Benjamin|date=2015-05-20|title=Ultrasensitive measurement of microcantilever displacement below the shot-noise limit |journal=Optica|language=en|volume=2|issue=5|pages=393|doi=10.1364/OPTICA.2.000393|arxiv=1405.4767|bibcode=2015Optic...2..393P|s2cid=118422029}}

;Uses of projection noise removal

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.{{Cite journal|last1=Nair|first1=Ranjith|last2=Tsang|first2=Mankei|date=2016-11-04|title=Far-Field Superresolution of Thermal Electromagnetic Sources at the Quantum Limit |journal=Physical Review Letters|volume=117|issue=19|pages=190801|doi=10.1103/PhysRevLett.117.190801|pmid=27858425|arxiv=1604.00937|bibcode=2016PhRvL.117s0801N|s2cid=25870660}}{{Cite journal|last1=Tsang|first1=Mankei|last2=Nair|first2=Ranjith|last3=Lu|first3=Xiao-Ming|date=2016-08-29|title=Quantum Theory of Superresolution for Two Incoherent Optical Point Sources |journal=Physical Review X|language=en|volume=6|issue=3|pages=031033|doi=10.1103/PhysRevX.6.031033|arxiv=1511.00552|bibcode=2016PhRvX...6c1033T|s2cid=32680254}} The diminishing projection noise has direct applications in communication protocols and nano-Nuclear Magnetic Resonance.{{Cite journal|last1=Maze|first1=J. R.|last2=Stanwix|first2=P. L.|last3=Hodges|first3=J. S.|last4=Hong|first4=S.|last5=Taylor|first5=J. M.|last6=Cappellaro|first6=P.|last7=Jiang|first7=L.|last8=Dutt|first8=M. V. Gurudev|last9=Togan|first9=E.|last10=Zibrov|first10=A. S.|last11=Yacoby|first11=A.|date=October 2008|title=Nanoscale magnetic sensing with an individual electronic spin in diamond |journal=Nature|language=en|volume=455|issue=7213|pages=644–647|doi=10.1038/nature07279|pmid=18833275|bibcode=2008Natur.455..644M|s2cid=136428582}}{{Cite journal|last1=Kong|first1=Xi|last2=Stark|first2=Alexander|last3=Du|first3=Jiangfeng|last4=McGuinness|first4=Liam P.|last5=Jelezko|first5=Fedor|date=2015-08-06|title=Towards Chemical Structure Resolution with Nanoscale Nuclear Magnetic Resonance Spectroscopy |journal=Physical Review Applied|volume=4|issue=2|pages=024004|doi=10.1103/PhysRevApplied.4.024004|arxiv=1506.05882|bibcode=2015PhRvP...4b4004K|s2cid=172297}}

;Other uses of entanglement

Entanglement can be used to improve upon existing atomic clocks{{cite journal|last1=Bollinger|first1=J. J .|last2=Itano|first2=Wayne M.|last3=Wineland|first3=D. J.|last4=Heinzen|first4=D. J.|date=1996-12-01|title=Optimal frequency measurements with maximally correlated states|journal=Physical Review A|volume=54|issue=6|pages=R4649–R4652|doi=10.1103/physreva.54.r4649|pmid=9914139|bibcode=1996PhRvA..54.4649B}}{{cite journal|last1=Marciniak|first1=Christian D. |last2=Feldker|first2=Thomas |last3=Pogorelov|first3=Ivan|last4=Kaubruegger|first4=Raphael|last5=Vasilyev|first5=Denis V.|last6=Van Bijnen|first6=Rick|last7=Schindler|first7=Philipp|last8=Zoller|first8=Peter|last9=Blatt|first9=Rainer|last10=Monz|first10=Thomas|date=2022-03-23|title=Optimal metrology with programmable quantum sensors|journal=Nature|volume=603|issue=7902 |pages=604–609|doi=10.1038/s41586-022-04435-4|pmid=35322252 |arxiv=2107.01860 |bibcode=2022Natur.603..604M |s2cid=245837971 }}{{Cite journal |last1=Franke |first1=Johannes |last2=Muleady |first2=Sean R. |last3=Kaubruegger |first3=Raphael |last4=Kranzl |first4=Florian |last5=Blatt |first5=Rainer |last6=Rey |first6=Ana Maria |last7=Joshi |first7=Manoj K. |last8=Roos |first8=Christian F. |date=2023-08-30 |title=Quantum-enhanced sensing on optical transitions through finite-range interactions |url=https://www.nature.com/articles/s41586-023-06472-z |journal=Nature |volume=621 |issue=7980 |pages=740–745 |language=en |doi=10.1038/s41586-023-06472-z |pmid=37648868 |arxiv=2303.10688 |bibcode=2023Natur.621..740F |s2cid=257632503 |issn=0028-0836}} or create more sensitive magnetometers.{{cite journal|last1=Auzinsh|first1=M.|last2=Budker|first2=D.|last3=Kimball|first3=D. F.|last4=Rochester|first4=S. M.|last5=Stalnaker|first5=J. E.|last6=Sushkov|first6=A. O.|last7=Yashchuk|first7=V. V.|date=2004-10-19|title=Can a Quantum Nondemolition Measurement Improve the Sensitivity of an Atomic Magnetometer?|journal=Physical Review Letters|volume=93|issue=17|page=173002|arxiv=physics/0403097|doi=10.1103/physrevlett.93.173002|pmid=15525071|bibcode=2004PhRvL..93q3002A|s2cid=31287682}}{{cite journal|last1=Guillaume|first1=Alexandre|last2=Dowling|first2=Jonathan P.|date=2006-04-27|title=Heisenberg-limited measurements with superconducting circuits|journal=Physical Review A|volume=73|issue=4|page=040304(R)|arxiv=quant-ph/0512144|doi=10.1103/physreva.73.040304|bibcode=2006PhRvA..73d0304G|s2cid=33820154}}

;Quantum radars

Quantum radar is also an active area of research. Current classical radars can interrogate many target bins while quantum radars are limited to a single polarization or range.{{Cite journal|last=Lanzagorta|first=Marco|date=2011-10-31|title=Quantum Radar|journal=Synthesis Lectures on Quantum Computing|language=en|volume=3|issue=1|pages=1–139|doi=10.2200/S00384ED1V01Y201110QMC005|s2cid=27569963 }} A proof-of-concept quantum radar or quantum illuminator using quantum entangled microwaves was able to detect low reflectivity objects at room-temperature – such may be useful for improved radar systems, security scanners and medical imaging systems.{{cite news |title=Scientists demonstrate quantum radar prototype |url=https://phys.org/news/2020-05-scientists-quantum-radar-prototype.html |access-date=12 June 2020 |work=phys.org |language=en}}{{cite news |title="Quantum radar" uses entangled photons to detect objects |url=https://newatlas.com/physics/quantum-radar-entangled-photons/ |access-date=12 June 2020 |work=New Atlas |date=12 May 2020}}{{cite journal |last1=Barzanjeh |first1=S. |last2=Pirandola |first2=S. |last3=Vitali |first3=D. |last4=Fink |first4=J. M. |title=Microwave quantum illumination using a digital receiver |journal=Science Advances |date=1 May 2020 |volume=6 |issue=19 |pages=eabb0451 |doi=10.1126/sciadv.abb0451 |pmid=32548249 |pmc=7272231 |arxiv=1908.03058 |bibcode=2020SciA....6..451B |doi-access=free }}

;Neuroimaging

In neuroimaging, the first quantum brain scanner uses magnetic imaging and could become a novel whole-brain scanning approach.{{cite news |title=Researchers build first modular quantum brain sensor, record signal |url=https://phys.org/news/2021-06-modular-quantum-brain-sensor.html |access-date=11 July 2021 |work=phys.org |language=en}}{{cite arXiv |last1=Coussens |first1=Thomas |last2=Abel |first2=Christopher |last3=Gialopsou |first3=Aikaterini |last4=Bason |first4=Mark G. |last5=James |first5=Tim M. |last6=Orucevic |first6=Fedja |last7=Kruger |first7=Peter |title=Modular optically-pumped magnetometer system |date=10 June 2021|class=physics.atom-ph |eprint=2106.05877 }}

;Gravity cartography of subterraneans

Quantum gravity-gradiometers that could be used to {{tooltip|2='gravity cartography'|map}} and investigate subterraneans are also in development.{{cite journal |last1=Stray |first1=Ben |last2=Lamb |first2=Andrew |last3=Kaushik |first3=Aisha |last4=Vovrosh |first4=Jamie |last5=Rodgers |first5=Anthony |last6=Winch |first6=Jonathan |last7=Hayati |first7=Farzad |last8=Boddice |first8=Daniel |last9=Stabrawa |first9=Artur |last10=Niggebaum |first10=Alexander |last11=Langlois |first11=Mehdi |last12=Lien |first12=Yu-Hung |last13=Lellouch |first13=Samuel |last14=Roshanmanesh |first14=Sanaz |last15=Ridley |first15=Kevin |last16=de Villiers |first16=Geoffrey |last17=Brown |first17=Gareth |last18=Cross |first18=Trevor |last19=Tuckwell |first19=George |last20=Faramarzi |first20=Asaad |last21=Metje |first21=Nicole |last22=Bongs |first22=Kai |last23=Holynski |first23=Michael |title=Quantum sensing for gravity cartography |journal=Nature |date=February 2022 |volume=602 |issue=7898 |pages=590–594 |doi=10.1038/s41586-021-04315-3 |pmid=35197616 |pmc=8866129 |bibcode=2022Natur.602..590S |language=en |issn=1476-4687}}{{Cite web |date=2022-02-27 |title=Quantum Gravity Sensor Breakthrough Paves Way for Groundbreaking Map of World Under Earth's Surface |url=https://scitechdaily.com/quantum-gravity-sensor-breakthrough-paves-way-for-groundbreaking-map-of-world-under-earth-surface/ |access-date=2022-03-02 |website=SciTechDaily |language=en-US}}

{{Reflist}}

{{Emerging technologies|quantum=yes|other=yes}}

Category:Quantum information science

Category:Sensors