Physics:Virtual state

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Short description: In quantum physics, a very short-lived, unobservable quantum state


Energy-level diagram showing the states involved in Raman spectra, including virtual energy states.

In quantum physics, a virtual state is a very short-lived, unobservable quantum state.[1]

In many quantum processes a virtual state is an intermediate state, sometimes described as "imaginary"[2] in a multi-step process that mediates otherwise forbidden transitions. Since virtual states are not eigenfunctions of any operator,[3] normal parameters such as occupation, energy and lifetime need to be qualified. No measurement of a system will show one to be occupied,[4] but they still have lifetimes derived from uncertainty relations.[5][6] While each virtual state has an associated energy, no direct measurement of its energy is possible[7] but various approaches have been used to make some measurements (for example see[8] and related work[9][10] on virtual state spectroscopy) or extract other parameters using measurement techniques that depend upon the virtual state's lifetime.[11] The concept is quite general and can be used to predict and describe experimental results in many areas including Raman spectroscopy,[12] non-linear optics generally,[5] various types of photochemistry,[13] and nuclear processes.[14]

See also

References

  1. ↑ "A glossary of terms in nuclear science and technology". Conference on Glossary of Terms in Nuclear Science and Technology. A series of nine sections. American Society of Mechanical Engineers. 1953. p. 61. https://books.google.com/books?id=LDkrAAAAYAAJ&q=%22virtual+state%22+fictitious+quantum&pg=PA61. 
  2. ↑ "Tunable Far IR Molecular Lasers Developed: Stimulated Raman scattering associated with a series of closely spaced rotational states is the key to wavelength tunability". Science (New York, N.Y.) 227 (4688): 736–7. February 1985. doi:10.1126/science.227.4688.736. PMID 17796721. 
  3. ↑ "Historical Development of Non-linear Optical Microscopy and Spectroscopy". Handbook of Biomedical Nonlinear Optical Microscopy. US: Oxford University Press. 2008. pp. 10. ISBN 978-0-19-516260-8. https://books.google.com/books?id=4mki1ThMgGYC&pg=PA10. 
  4. ↑ Wardle, David (1999). Raman scattering in optical fibres (Thesis). p. 22. hdl:2292/433.
  5. ↑ 5.0 5.1 Nonlinear Optics and Laser Spectroscopy. Alpha Science International, Limited. 2001. p. 139. ISBN 978-81-7319-354-5. https://books.google.com/books?id=bnuGcAZR14IC&pg=PA139. 
  6. ↑ "Microscopic theory of nonlinear optics.". Non-Linear Optical Properties of Matter. Dordrecht: Springer. 2006. pp. 3. ISBN 978-1-4020-4849-4. https://books.google.com/books?id=eeE8OrohX3sC&pg=PA3. 
  7. ↑ "The Dyson Perturbation Expansion of the Evolution Operator". Principles of quantum scattering theory. CRC Press. 2004. p. 70. ISBN 978-0-7503-0496-2. https://books.google.com/books?id=V9YY6Bmg6ngC&pg=PA70. 
  8. ↑ "Entangled-Photon Virtual-State Spectroscopy". Physical Review Letters 80 (16): 3483–3486. April 1998. doi:10.1103/PhysRevLett.80.3483. Bibcode: 1998PhRvL..80.3483S. http://people.bu.edu/teich/pdfs/PRL-80-3483-1998.pdf. 
  9. ↑ "Entangled biphoton virtual-state spectroscopy of the A2Σ+–X2Π system of OH". Chemical Physics Letters 396 (4): 323–328. 1 October 2004. doi:10.1016/j.cplett.2004.08.051. Bibcode: 2004CPL...396..323K. 
  10. ↑ "Quantum spectroscopy of an organic material utilizing entangled and correlated photon pairs". Linear and Nonlinear Optics of Organic Materials VII (International Society for Optics and Photonics) 6653: 66530V. 2007. doi:10.1117/12.745492. Bibcode: 2007SPIE.6653E..0VL. 
  11. ↑ "Measuring photon bunching at ultrashort timescale by two-photon absorption in semiconductors". Nature Physics 5 (4): 267–270. 13 April 2009. doi:10.1038/nphys1218. Bibcode: 2009NatPh...5..267B. 
  12. ↑ Fourier Transform Infrared Spectrometry. 83 (second ed.). Wiley-Interscience. 2007. p. 16. ISBN 978-0-470-10629-7. https://books.google.com/books?id=ZecrNiUkHToC&q=%22&pg=PA16. 
  13. ↑ "Two-photon physical, organic, and polymer chemistry: theory, techniques, chromophore design, and applications.". Advances in Photochemistry (John Wiley and Sons) 29: 111–354 (116). January 2007. doi:10.1002/047003758X.ch3. ISBN 978-0-471-68240-0. https://books.google.com/books?id=Ik0bDuWzEHYC&pg=PA118. 
  14. ↑ "Virtual coulomb excitation in nucleon transfer". Proceedings of the National Academy of Sciences of the United States of America 57 (4): 849–55. April 1967. doi:10.1073/pnas.57.4.849. PMID 16591541. Bibcode: 1967PNAS...57..849B. 



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