Lect10 - "A vast time bubble has been projected into the...

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“A vast time bubble has been projected into the future to the precise moment of the end of the universe. This is, of course, impossible.” --D. Adams, The Hitchhiker’s Guide to the Galaxy “There is light at the end of the tunnel.” -- proverb “The light at the end of the tunnel is just the light of an oncoming train.” --R. Lowell
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Physics Colloquium Physics Colloquium “Spin Based Test-beds for Quantum Information Processing” Professor David G. Cory Massachusetts Institute of Technology Department of Nuclear Science and Engineering February 14, 2008 4:00 pm, Room 141 Loomis Lab Special (Optional) Lecture Special (Optional) Lecture “Quantum Information” z One of the most modern applications of QM z quantum computing z quantum communication – cryptography, teleportation z quantum metrology z PGK will give a special 214-level lecture on this topic z Sunday, Feb. 17 z 4 pm, 151 Loomis z Attendance is optional, but encouraged.
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Next week: Laboratory 4 Next week: Laboratory 4 θ Slit Eyepiece Light source ndeflected beam Deflected beam Grating Light shield Cross hairs Collimating lens Focusing lens 2 13.6 n eV E n =
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Good web site for animations http://www.falstad.com/qm1d/ Overview of the rest of the course This week – the time-dependent Schr. Eq. Tunneling, radioactive decay, Schrodinger’s cat, . . . Next week – quantum states in 3 dimensions, electron spin H atom, exclusion principle, periodic table of atoms Last week – molecules and solids, consequences of Q. M. Metals, insulators, semiconductors, superconductors, lasers, . .
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Barrier Penetration and Tunneling x 0L U 0 x U(x) E U(x) 0 x AB C B A nucleus
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Overview Overview z Tunneling of quantum particles z Scanning Tunneling Microscope (STM) z Nuclear Decay z Solar Fusion z “Tunneling’ of atoms in the NH 3 molecule: the NH 3 Maser
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z Due to “barrier penetration”, the electron density of a metal actually extends outside the surface of the metal! E F Occupied levels Work function Φ V o Assume that the work function (i.e., the energy difference between the most energetic conduction electrons and the potential barrier at the surface) of a certain metal is Φ = 5 eV . Estimate the distance x outside the surface of the metal at which the electron probability density drops to 1/1000 of that just inside the metal. 1000 1 ) 0 ( ) ( 2 2 2 = Kx e x ψ x = 0 x nm K x 3 . 0 1000 1 ln 2 1 = Leaky” Particles: Revisited Leaky” Particles: Revisited () 1 0 22 2 5 2 2 11.5 1.505 ee mm eV KV E n m he V n m ππ =− = = = using
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Application: Application: Tunneling Microscopy Tunneling Microscopy z Due to the quantum effect of “barrier penetration,” the electron density of a material extends beyond its surface: material STM tip STM tip material ~ 1 nm x Metal tip One can exploit this to measure the electron density on a material’s surface: Na atoms on metal: Real STM tip STM images DNA Double Helix: http://www.quantum-physics.polytechnique.fr/en/
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Tunneling: Key points Tunneling: Key points z In quantum mechanics a particle can penetrate into a barrier where it
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Lect10 - "A vast time bubble has been projected into the...

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