EE201/MSE207 Applied Quantum Mechanics Lecture 1: Introduction Quantum mechanics (QM) is one of two theories of 20 th century physics, which considerably changes our understand of nature. - Relativity changed our understanding of space and time. - QM changed the logic of thinking about microscopic objects. Main philosophical ideas: wave-particle duality and indeterminism πΉ = βπ (Planck-Einstein) for particles β = 1.05 Γ 10 β34 J ο s 2πβ π = π (de Broglie) for particles Estimates: 2πβ 1.504 eV 1.226 nm Electron: π = 2π π πΉ = 1 nm = πΉ πΉ[eV] 2ππ 2πβπ 1.240 πm Photon: π = π = = πΉ πΉ[eV]
Prehistory of Quantum Mechanics 1) 1900 Max Planck: suggested discrete absorption and emission of light to explain experimental formula for black-body radiation (Nobel Prize 1918) πΉ = βπ = βπ β = 6.63 Γ 10 β34 J ο s β = 1.05 Γ 10 β34 J ο s 2) 1905 Albert Einstein: theory of photoelectric effect (Nobel Prize 1921) ππ€ 2 βπ = Ξ¦ + Ξ¦ is work function (ionization energy) 2 3) 1913 Niels Bohr: model of atom (Nobel Prize 1922) ππ€π = πβ Discrete atomic spectra and Rutherfordβs experiments (1910 -1911, N.P. 1908) 4) 1923 Arthur Compton: scattering of X-rays on electrons (Nobel Prize 1927) 5) 1923 Louis de Broglie: matter waves (theory only, in 1927 confirmed for π = 2πβ electrons, Nobel Prize 1929) π βBirthβ of Quantum mechanics: 1927 (5 th Solvay conference, Brussels)
Classical mechanics vs. Quantum Mechanics (one particle in one dimension) Classical mechanics: π 2 π¦ ππ¦ Position π¦(π’) , velocity π€ π’ = ππ’ , acceleration π π’ = ππ’ 2 ππ(π¦) πΊ = β for a conservative system, π(π¦) is potential energy ππ¦ πΊ Main evolution equation: π = π π 2 π¦ ππ’ 2 = β 1 ππ initial conditions: ο π¦(π’) π¦ 0 , π¦(0) π ππ¦ Quantum mechanics: Main evolution equation: SchrΓΆdinger equation ππ’ = β β 2 π 2 Ξ¨ πβ πΞ¨ Ξ¨(π¦, π’) is a complex function, characterizing ππ¦ 2 + πΞ¨ 2π the particle state (wave function) 2 ππ¦ is the probability to find the particle between π¦ and π¦ + ππ¦ Ξ¨ π¦, π’ at time π’ (if observed!) Indeterminacy: particle does not have position (still debates about philosophy)
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