Quantum optics Set 3

Tom Schobert
Flashcards by , created almost 2 years ago

Flashcards on Quantum optics Set 3, 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
BEC with attractive interactions - scattering length a <0 → negative cooling (collapse sketch) - But zero point energy (Quantum pressure)→ stabilization
BEC-Dispersionrelation weakly interacting BEC: hν=E(k)=√(ħω_k^0 (ħω_k^0+2μ)) Phononen-Limit: hν0<<2μ → E(k)=p√(c_s ) Particle limit: E(k)≈hν_0+hΔν measure dispersion by scattering
BEC-Superfluidity movement without resistance v>vc → scattering v<vc → superfluidity No excitation possible if |qi| is small enough |q_i |/m_p >c_s;E(p ⃗ )/p ⃗ =c_s
BEC in optical lattices - fluctuating atom number, well defined phase relation - interference pattern
Thomas-Fermi-Limit neglect kinetic term in GPE Vext is harmonic size of BEC: R_TF=an_0 ((15N_a)/(an_0 ))^(1/5)
Scattering length - appears in atomic cross section - determined by binding energy of last bound vibrational state - positive or negative - determines (non-)attractive BEC - tunable by feshbach resonances
Vorticies in a BEC macroscopic condensate wave function quantized circulation in order to fulfill angular momentum criteria the wavefunction vanishes in the „eye of the vortex“ because there it should rotate infinitely fast
Principle of Atom Interferometry - splitting of a wave (function) into two ways - Phase shift inbetween the two ways →different probabilities→ interference - Measure: o gravitation o rotations o fundamental physical constants o atomic properties (atomic polarizability)
Mach-Zehnder Interferometer - phase shift at BS2: π
Interfering BEC preparation of a BEC in a magnetic trap splitting the BEC with a laser (blue detuned) release both parts of the BEC |ψ(t)|^2=|ψ_A^* (t) ψ_B (t)|^2 one gets an interference pattern with: δ_2π==λ_(dB,rel)
Diffraction by grating 3 gating Δ_detector=Δ_geom+Δ_int=Φ_A =Φ_B
adiabatic following when does a moving atomic moment keep it's orientation relative to magnetic field? ω_Larmor=(gm_F μ_B)/ħ |B| ω_rot≪ω_Larmor at B=0: atom does not know how to orientate → half is lost
Quadrupole and Ioffe-Pritchard Trap - Quadrupole: o pair of coils in anti „helmholtz“ configuration o low-field seekers can turn into high field seekers - Ioffe-Pritchard Trap o Main adavantage: No majorana losses
Optical pumping - transfer the atom with σ+ or σ- light into a desired other mF state
Dark states - state , which does not change under the influence of light - cannot absorb an incident photon - for cooling: o no population in excited state o destructive interference of excitation amplitudes o coherent superpositions