Quantum optics-Set 1

Tom Schobert
Flashcards by , created almost 2 years ago

Flashcards on Quantum optics-Set 1, created by Tom Schobert on 09/21/2017.

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Tom Schobert
Created by Tom Schobert almost 2 years ago
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Question Answer
π and π/2-Puls - π/2-Puls magtransfer superpos state into excited state - mixture will be not completely transferred - Rabifreq:  π/ R0: the whole population in excited state  π/2 R0: equal superposition
Fluorescence and natural linewidth - natural: γ10=FWHM at atomic transition - fluorescence: fast decay
Absorption imaging of ultracold Atoms - lens=imaging system - Bild des Schattens der Atome - Off resonant laser
Suitable Atoms for laser cooling(Alkali and Alkaline Earths) - almost closed two-level transition - availability of tonable narrow-bandlasers - vapour pressure of the atomic gas in the range of mbar(102Pa) at reachable T (<1500°C) - Alkali Atoms: n2S1/2 → n2P3/2 transition - all isotopes posses spin (n2P1/2)[hyperfine structure] F=I-1/2; F=I+1/2 - Alkaline: 2 electrons in s-state n1S0 → n1P1 transition
Dipole selection rules - s‘=s - L‘=L±1 - J‘=J; J±1 - F‘=F; F±1 - mF‘=mF; mF ±1
Polarisation - ε0: describes linearly polarized light (mF‘=mF;π transition; quantization axis parallel to polarisation) - ε+1: describes circularly polarized light (mF‘=mF+1;σ+ transition; quantization axis parallel to direction of propagation) - ε-1: describes circularly polarized light (mF‘=mF-1;σ- transition; quantization axis parallel to direction of propagation)
Principle of slowing atoms momentum transfer due to absorption undirectional emission (spontaneous emission) slowing force: (formula)
Doppler effect - due to doppler effect, the effective detuning depends on atom velocity - adjust such that δeff=0 - solutions:  white laser(all frequencies)  adjust laser freq. (only pulsed possible)  transition freq. adjust → Zeeman slower
Zeeman slower Absorption Laserlicht und folgende Reemission von Fluoreszenzphotonen: Bremsen Magnetfeld: Zeemaneffekt vs. Dopplerverschiebung - B(z) has same shape as v(z)
Optical Molasses two counter propagating lasers to get rid of constant force of the dissipative force (F_OM ) ⃗=-β ̃v ⃗ β depends on δ(<0: red detuned) → velocity dep. friction force
Doppler limit Cooling rate in optical molasses equals heat rate due to isotropic emission T_Doppler1D= ħ γ_10/(2k_B )≈100μK
Elastic collisions „good collisions“ total kinetic energy is conserved only kinetic redistribution for distinguishable particles σ=4πa^2 for undistinguishable particles r_Boson=8πa^2,σ_Fermion=0 λ=1/nσ Important for evaporative cooling
Inelastic collisions - „Bad collisions“ - loss of energy (kinetic into internal) and far particles - Restgas collisions - Dipole relaxion (Coupling of two dipoles ↑↑) - 3 body-recombination (forming a molecule)
BEC-Expansion - uncertainty principle ΔpΔt≥π/2 - interactions between the atoms
Measuring velocity distributions - sketch( laser beam frequency vs. velocity distribution) - same shape of velocity distribution than fluorescence signal