Coherent control

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Coherent control is a form of quantum control that uses the wave properties of matter to control the evolution of a quantum system over time in the desired manner.

Typically, the relative phases between different parts of the wave function of a quantum system are influenced with the help of external electromagnetic fields in such a way that constructive or destructive interference of the matter waves is generated. The part of the electromagnetic spectrum from which the fields originate is only relevant insofar as resonant transitions are usually driven. This can be done, for example, with the help of shaped femtosecond laser pulses that drive electronic transitions in atoms or molecules, but also with microwave pulses that drive transitions between rotation levels in molecules or couple to superconducting qubits .

development

The research field of coherent control developed from the mid-1980s in the field of physical chemistry, when ways to control chemical reactions were sought, initially through a series of theoretical proposals. The first experimental implementations of these proposals took place in the 1990s using the electric field of femtosecond lasers , which can be specifically influenced in terms of their amplitude , phase and polarization . Today ideas of coherent control are found in numerous areas of physics , e.g. B. solid state physics or quantum information , application.

Coherent control as a time-dependent process

In excitation-interrogation experiments , a first electrical field pulse generates a wave packet . The wave packet that changes over time is queried spectroscopically by a second pulse that is radiated in with a time delay. The duration of the time delay is proportional to the relative phase of the wave packets generated by the first and second pulse. This technology is used in particular in photoelectron spectroscopy .

Coherent control as interference between "quantum paths"

If the transition from one quantum mechanical state to another occurs via two different excitation options, e.g. B. by the absorption of one or three photons, then the occupation of the target state is dependent on the relative phase of the electric fields that drive the transition.

Other forms of coherent control

Another possibility to control the time development of a quantum system by phase manipulation is provided by the so-called STIRAP method (STIRAP = Stimulated Raman adiabatic passage) or, more generally, the dynamic generation of dark states with the help of interference.

literature

  • Rice, Stuart Alan, and Meishan Zhao. Optical control of molecular dynamics. New York: John Wiley, 2000.
  • Moshe Shapiro and Paul Brumer : Quantum control of molecular processes . 2nd ed. Weinheim 2012. ISBN 978-3-527-40904-4
  • Paul Brumer, Moshe Shapiro: Controlling chemical reactions with lasers . In: Spectrum of Science . No. 5 , 1995, p. 70 ( online [accessed July 19, 2019]).

Web links

Individual evidence

  1. ↑ Tannor, David J., and Stuart A. Rice. "Control of selectivity of chemical reaction via control of wave packet evolution." The Journal of Chemical Physics 83, no.10 (1985): 5013-5018.
  2. ↑ Tannor, David J., Ronnie Kosloff, and Stuart A. Rice. "Coherent pulse sequence induced control of selectivity of reactions: Exact quantum mechanical calculations." The Journal of Chemical Physics 85, no.10 (1986): 5805-5820.
  3. ^ A b Brumer, Paul, and Moshe Shapiro. "Control of unimolecular reactions using coherent light." Chemical Physics Letters 126, no. 6 (1986): 541-546.
  4. ↑ AM Weiner: Femtosecond pulse shaping using spatial light modulators . In: Review of Scientific Instruments . 71, No. 5, 2000, pp. 1929-1960. bibcode : 2000RScI ... 71.1929W . doi : 10.1063 / 1.1150614 .
  5. ↑ Introduction to Quantum Mechanics, A Time Dependent Perspective, David Tannor .
  6. ↑ Nikolay V. Vitanov, Andon A. Rangelov, Bruce W. Shore, Klaas Bergmann: Stimulated Raman adiabatic passage in physics, chemistry, and beyond . In: Reviews of Modern Physics . 89, No. 1, 2017, ISSN  0034-6861 . arxiv : 1605.00224 . bibcode : 2017RvMP ... 89a5006V . doi : 10.1103 / RevModPhys.89.015006 .
  7. ^ Klaas Bergmann, Nikolay V. Vitanov, Bruce W. Shore: Perspective: Stimulated Raman adiabatic passage: The status after 25 years . In: The Journal of Chemical Physics . 142, No. 17, 2015, ISSN  0021-9606 , P. 170901. bibcode : 2015JChPh.142q0901B . doi : 10.1063 / 1.4916903 .