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,[13] various types of photochemistry,[14] and/or nuclear processes.[15]

See alsoEdit


  1. ^ A glossary of terms in nuclear science and technology: a series of nine sections By National Research Council (U.S.). Conference on Glossary of Terms in Nuclear S American Society of Mechanical Engineers, 1953 page 61
  2. ^ Science, Volume 227 American Association for the Advancement of Science, HighWire Press, JSTOR 1985 page 736
  3. ^ Barry R. Masters, Peter T. C. So Handbook of Biomedical Nonlinear Optical Microscopy Oxford University Press US, 2008 ISBN 0-19-516260-9 ISBN 978-0-19-516260-8 page 10
  4. ^ David Alan Wardle Raman Scattering in Optical Fibres, thesis Doctor of Philosophy in Physics The University of Auckland, January 1999 page 22
  5. ^ Nonlinear Optics and Laser Spectroscopy By S C Abbi, S. A. Ahmad page 139 ISBN 81-7319-354-1, ISBN 978-81-7319-354-5
  6. ^ Non-linear optical properties of matter: from molecules to condensed phases By Manthos G. Papadopoulos, Andrzej Jerzy Sadlej, Jerzy Leszczynski page 3 Springer, 2006 ISBN 1-4020-4849-1, ISBN 978-1-4020-4849-4
  7. ^ Dzevad Belkic Principles of quantum scattering theory page 70 CRC Press, 2004 ISBN 0-7503-0496-0, ISBN 978-0-7503-0496-2
  8. ^ Bahaa E. A. Saleh, Bradley M. Jost, Hong-Bing Fei, and Malvin C. Teich Entangled-Photon Virtual-State Spectroscopy VOLUME 80, NUMBER 16 PHY S I CAL REV I EW LETTERS 20 APRIL 1998 S0031-9007(98)05928-6 page 3483
  9. ^ Jun KojimaCorresponding Author Contact Information, a, E-mail The Corresponding Author and Quang-Viet Nguyen Entangled biphoton virtual-state spectroscopy of the A2Σ+–X2Π system of OH Chemical Physics Letters Volume 396, Issues 4-6, 1 October 2004, Pages 323-328
  10. ^ Dong-Ik Lee and Theodore Goodson III Quantum spectroscopy of an organic material utilizing entangled and correlated photon pairs Proc. SPIE, Vol. 6653, 66530V (2007); doi:10.1117/12.745492
  11. ^ F. Boitier, A. Godard, E. Rosencher & C. Fabre Measuring photon bunching at ultrashort timescale by two-photon absorption in semiconductors Nature Physics 5, 267 - 270 (2009) Published online: 15 March 2009 doi:10.1038/nphys1218
  12. ^ Peter R. Griffiths, James A. De Haseth Fourier Transform Infrared Spectrometry, Volume 83 second ed, Wiley-Interscience, 2007 ISBN 0-470-10629-8 ISBN 978-0-470-10629-7 page 16
  13. ^ S C Abbi, S. A. Ahmad Nonlinear Optics and Laser Spectroscopy, Alpha Science Int' Ltd., 2001 ISBN 81-7319-354-1 ISBN 978-81-7319-354-5 page 139
  14. ^ Douglas C. Neckers, William S. Jenks, Thomas Wolff Advances in Photochemistry, Volume 29 John Wiley and Sons, 2006 ISBN 0-471-68240-3 ISBN 978-0-471-68240-0 page 116