Virtual state (physics)

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The term virtual state is commonly used to refer to two different types of states in physical systems. It may refer to a very short-lived, unobservable quantum state or a real, but unstable, state. Early definitions of the term (for example, see [1]) appear to distinguish the virtual state from the "virtual quantum."

Quantum State[edit]

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 anything ,[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]

Unstable State[edit]

The term virtual state can also be used to refer to bound or transient states which can decay into free states or relax at some finite rate.[16] This state may be the metastable state of a certain class of Feshbach resonance, "A special case of a Feshbach-type resonance occurs when the energy level lies near the very top of the potential well. Such a state is called 'virtual'"[17] and may be further contrasted to a shape resonance depending on the angular momentum.[18] Because of their transient existence, they can require special techniques for analysis and measurement, for example.[19][20][21][22]

See also[edit]


  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
  16. ^ On the Dynamics of Single-Electron Tunneling in Semiconductor Quantum Dots under Microwave Radiation Dissertation Physics Department of Ludwig-Maximilians-Universitat Munchen by Hua Qin from Wujin, China 30 July 2001, Munchen
  17. ^ Schulz George Resonances in Electron Impact on Atoms and Diatomic Molecules Reviews of Modern Physics vol 45 no 3 pp378-486 July 1973
  18. ^ Donald C. Lorents, Walter Ernst Meyerhof, James R. Peterson Electronic and atomic collisions: invited papers of the XIV International Conference on the Physics of Electronic and Atomic Collisions, Palo Alto, California, 24-30 July, 1985 North-Holland, 1986 ISBN 0-444-86998-0, ISBN 978-0-444-86998-2 page 800
  19. ^ D. Field1 *, N. C. Jones1, S. L. Lunt1, and J.-P. Ziesel2 Experimental evidence for a virtual state in a cold collision: Electrons and carbon dioxide Phys. Rev. A 64, 022708 (2001) 10.1103/PhysRevA.64.022708
  20. ^ B. A. Girard and M. G. Fuda Virtual state of the three nucleon system Phys. Rev. C 19, 579 - 582 (1979) 10.1103/PhysRevC.19.579
  21. ^ Tamio Nishimura * and Franco A. Gianturco Virtual-State Formation in Positron Scattering from Vibrating Molecules: A Gateway to Annihilation Enhancement Phys. Rev. Lett. Volume 90Issue 18 Phys. Rev. Lett. 90, 183201 (2003) 10.1103/PhysRevLett.90.183201
  22. ^ Kurokawa, Chie; Masui, Hiroshi; Myo, Takayuki; Kato, Kiyoshi Study of the virtual state in νc10Li with the Jost function method American Physical Society, First Joint Meeting of the Nuclear Physicists of the American and Japanese Physical Societies October 17 - 20, 2001 Maui, Hawaii Meeting ID: HAW01, abstract #DE.004