Editing Squeezed coherent state (section)

==Applications==
Squeezed states of the light field can be used to enhance precision measurements. For example, phase-squeezed light can improve the phase read out of [[interferometry|interferometric measurements]] (see for example [[gravitational wave]]s). Amplitude-squeezed light can improve the readout of very weak [[spectroscopy|spectroscopic signals]].<ref>{{Cite journal|last=Polzik|first=E. S.|date=1992-01-01|title=Spectroscopy with squeezed light|journal=Physical Review Letters|volume=68|issue=20|pages=3020–3023|doi=10.1103/PhysRevLett.68.3020|pmid=10045587|bibcode=1992PhRvL..68.3020P|url=https://authors.library.caltech.edu/3302/1/POLprl92.pdf|type=Submitted manuscript}}</ref>

Spin squeezed states of atoms can be used to improve the precision of [[atomic clock]]s.<ref>{{cite journal|last1=Leroux|first1=Ian D.|last2=Schleier-Smith|first2=Monika H.|last3=Vuletić|first3=Vladan|s2cid=4514687|title=Orientation-Dependent Entanglement Lifetime in a Squeezed Atomic Clock|journal=Physical Review Letters|date=25 June 2010|volume=104|issue=25|page=250801|doi=10.1103/PhysRevLett.104.250801|arxiv = 1004.1725 |bibcode = 2010PhRvL.104y0801L|pmid=20867356}}</ref><ref>{{cite journal|last1=Louchet-Chauvet|first1=Anne|last2=Appel|first2=Jürgen|last3=Renema|first3=Jelmer J|last4=Oblak|first4=Daniel|last5=Kjaergaard|first5=Niels|last6=Polzik|first6=Eugene S|s2cid=119112907|title=Entanglement-assisted atomic clock beyond the projection noise limit|journal=New Journal of Physics|date=28 June 2010|volume=12|issue=6|pages=065032|doi=10.1088/1367-2630/12/6/065032|arxiv = 0912.3895 |bibcode = 2010NJPh...12f5032L }}</ref> This is an important problem in atomic clocks and other sensors that use small ensembles of cold atoms where the [[quantum noise|quantum projection noise]] represents a fundamental limitation to the precision of the sensor.<ref>{{cite journal|last1=Kitagawa|first1=Masahiro|last2=Ueda|first2=Masahito|title=Squeezed spin states|journal=Physical Review A|date=1 June 1993|volume=47|issue=6|pages=5138–5143|doi=10.1103/PhysRevA.47.5138|bibcode = 1993PhRvA..47.5138K|pmid=9909547 |hdl=11094/77656|url=https://ir.library.osaka-u.ac.jp/repo/ouka/all/77656/PhysRevA_47_06_005138.pdf |hdl-access=free}}</ref>

Various squeezed coherent states, generalized to the case of many [[degrees of freedom (physics and chemistry)|degrees of freedom]], are used in various calculations in [[quantum field theory]], for example [[Unruh effect]] and [[Hawking radiation]], and generally, particle production in curved backgrounds and [[Bogoliubov transformation]]s.

Recently, the use of squeezed states for [[quantum information processing]] in the continuous variables (CV) regime has been increasing rapidly.<ref>{{cite journal|last1=Braunstein|first1=Samuel L.|last2=van Loock|first2=Peter|s2cid=118990906|title=Quantum information with continuous variables|journal=Reviews of Modern Physics|date=29 June 2005|volume=77|issue=2|pages=513–577|doi=10.1103/RevModPhys.77.513|arxiv = quant-ph/0410100 |bibcode = 2005RvMP...77..513B }}</ref> Continuous variable quantum optics uses squeezing of light as an essential resource to realize CV protocols for quantum communication, unconditional quantum teleportation and one-way quantum computing.<ref>{{cite journal|last1=Furusawa|first1=A.|title=Unconditional Quantum Teleportation|journal=Science|date=23 October 1998|volume=282|issue=5389|pages=706–709|doi=10.1126/science.282.5389.706|bibcode = 1998Sci...282..706F|pmid=9784123 }}</ref><ref>{{cite journal|last1=Menicucci|first1=Nicolas C.|last2=Flammia|first2=Steven T.|last3=Pfister|first3=Olivier|s2cid=1307950|title=One-Way Quantum Computing in the Optical Frequency Comb|journal=Physical Review Letters|date=22 September 2008|volume=101|issue=13|page=13501|doi=10.1103/PhysRevLett.101.130501|arxiv = 0804.4468 |bibcode = 2008PhRvL.101m0501M|pmid=18851426}}</ref> This is in contrast to quantum information processing with single photons or photon pairs as qubits. CV quantum information processing relies heavily on the fact that squeezing is intimately related to quantum entanglement, as the quadratures of a squeezed state exhibit sub-shot-noise{{clarify|reason=Needs a definition. Does it mean sub-Poissonian? If so, then the claim is likely to be false.|date=September 2016}} quantum correlations.