Ultrastrong spin-motion coupling in nanofjber-based optical traps Alexandre Dareau*, Y. Meng, P. Schneeweiss & A. Rauschenbeutel VCQ – TU Wien – Atominstitut (Vienna, Austria) * now at Laboratoire Charles Fabry, IOGS (Palaiseau, France)
Nanofjber-based optical traps Optical nanofjber evanescent light fjeld 500 nm 125 µm [Vetsch et al. , PRL 104 , 203603 (2010)] Trapping atoms atom (cesium) light-assisted collisions during loading → max. 1 atom / site typically : N = 10 2 – 10 3 atoms OD = 1 – 10 red detuned light blue detuned light (1064 nm, attractive) (783 nm, repulsive) 1 Congrès Général SFP 2019 – Nantes Alexandre Dareau
Trapping atoms in evanescent light fjelds Fictitious magnetic fjeld ! [Cohen-Tannoudji & Dupont-Roc, PRA 5 , 968 (1972)] polarization evanescent gradient of vector light fjeld gradient ac Stark shift (size ~ λ) analogous to a Zeeman interaction with depends on the atom’s spin state a gradient of fjctitious magnetic fjeld With our trap confjguration, to fjrst order : linear gradient nanofjber 2 Congrès Général SFP 2019 – Nantes Alexandre Dareau
What is the efgect on the atoms ? « natural » Spin-motion coupling quantization axis (Cesium, F=4) atoms in nanofjber based optical trap harmonic Zeeman « spin-motion » coupling oscillator shift CQED model(s) quantized N-level Atom-light coupling light fjeld system (Jaynes-Cummings/Dicke) (in cavity) (atom[s]) [Schneeweiss, Dareau & Sayrin , PRA 98 , 021801(R) (2018)] 3 Congrès Général SFP 2019 – Nantes Alexandre Dareau
Looking for an experimental signature... Our probe : fmuorescence spectroscopy heterodyne detection power spectral density (PSD) yields energy spectrum excitation beam local SPCM oscillator radial (x) beatnote ~ 174 kHz central frequency (10 MHz) for ofg-resonant spin-motion coupling azimuthal (y) ~ 96 kHz axial (z) → yields trap frequencies ~ 247 kHz (transitions from ground state to fjrst excited motional states) 4 Congrès Général SFP 2019 – Nantes Alexandre Dareau
Experimental signature of the spin-motion coupling ! ofg-resonant coupling resonant coupling → vacuum Rabi splitting dressed states motional Rabi frequency state coupling 5 Congrès Général SFP 2019 – Nantes Alexandre Dareau
Experimental signature of the spin-motion coupling ! Scanning across resonance [Dareau et al., PRL 121 , 253603 (2018)] Trap frequencies 0 f x = 149(2) kHz = 1 Power n z f y = 93(2) kHz y x , Spectral 3 - = Density f z = 243(5) kHz m F 0 (a. u.) m F = -4, n z = 1 Energy (kHz) Rabi frequency (for n=1) Ω x = 2π × 35(1) kHz m F = -4, n x = 1 Ω y = 2π × 36(1) kHz m F = -4, n y = 1 Ω x / ω x = 0.24(2) m F = -4, n xyz = 0 Ω y / ω y = 0.38(2) Zeeman shift ΔE (kHz) ultra-strong coupling ! + possible to increase coupling strength even further (e.g. in optical lattices) [Schneeweiss et al., PRA 98 , 021801(R) (2018)] 6 Congrès Général SFP 2019 – Nantes Alexandre Dareau
Tuning the coupling strength Idea : compensate the vector ac Stark shift using fiber-guided laser at the “tune-out” wavelength (λ=880 nm) scalar polarizability vanishes → do not afgect scalar trapping potential → pure” fjctitious magnetic fjeld “ Experiment : reduction of vacuum Rabi splitting looking at direct transitions between excited dressed states yields Rabi splitting Rabi splitting decreases when tune-out laser power increases total compensation at ~ 400µW 7 Congrès Général SFP 2019 – Nantes Alexandre Dareau
Conclusion & outlook Ultra-strong spin-motion coupling naturally present in nanofjber-based optical traps (& in optical microtraps) possible to tune with additional light fjeld analogy with CQED (Jaynes-Cummings / Dicke) Outlook : tunability Outlook : CQED increase coupling strength increase coupling strength Dicke model (F=4 N=8 atoms) → “deep-strong coupling regime” (coupling > trap frequency) dynamical tuning / quenches Ω(t) with variation faster than trap oscillation period. Phase transition in the “mesoscopic” regime (N < ∞ ) ? Dynamical Casimir efgect ? Note : also in optical lattices >> Schneeweiss et al., PRA 98, 021801(R) (2018) 8 Congrès Général SFP 2019 – Nantes Alexandre Dareau
Thank you for your attention ! Slides available on www.adphys.eu References : Y. Meng, A. Rauschenbeutel, P. Schneeweiss & AD Observation of Ultrastrong Spin-Motion Coupling for Cold Atoms in Optical Microtraps, A. Dareau, Y. Meng, P. Schneeweiss, and A. Rauschenbeutel PRL 121 , 253603 (2018) [arXiv:1809.02488] Near-ground-state cooling of atoms optically trapped 300nm away from a hot surface, Y. Meng, A. Dareau, P. Schneeweiss, and A. Rauschenbeutel PRX 8 , 031054 (2018) [arXiv:1712.05749] Cold-atom based implementation of the quantum Rabi model (theory), P. Schneeweiss, A. Dareau, and C. Sayrin @adphys PRA 98 , 021801(R) (2018) [arXiv:1706.07781] 9 Congrès Général SFP 2019 – Nantes Alexandre Dareau
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