10474782
Description
Flashcards by Tom Schobert, updated more than 1 year ago
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Created by Tom Schobert
about 8 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 |
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