Ultrastrong spin-motion coupling in nanofjber-based optical traps - - PowerPoint PPT Presentation

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)

Congrès Général SFP 2019 – Nantes Alexandre Dareau

Nanofjber-based optical traps

red detuned light (1064 nm, attractive) blue detuned light (783 nm, repulsive)

Optical nanofjber

[Vetsch et al., PRL 104, 203603 (2010)] atom (cesium) 125 µm 500 nm evanescent light fjeld

light-assisted collisions during loading → max. 1 atom / site typically : N = 102 – 103 atoms OD = 1 – 10 1

Trapping atoms

Congrès Général SFP 2019 – Nantes Alexandre Dareau

Trapping atoms in evanescent light fjelds

Fictitious magnetic fjeld !

2

[Cohen-Tannoudji & Dupont-Roc, PRA 5, 968 (1972)] depends on the atom’s spin state

evanescent light fjeld gradient of vector ac Stark shift

analogous to a Zeeman interaction with a gradient of fjctitious magnetic fjeld (size ~ λ)

polarization gradient With our trap confjguration, to fjrst order : linear gradient

nanofjber

Congrès Général SFP 2019 – Nantes Alexandre Dareau

What is the efgect on the atoms ?

Spin-motion coupling

3

« natural » quantization axis

harmonic

• scillator

« spin-motion » coupling Zeeman shift quantized light fjeld (in cavity) N-level system (atom[s]) Atom-light coupling

[Schneeweiss, Dareau & Sayrin, PRA 98, 021801(R) (2018)]

atoms in nanofjber based optical trap CQED model(s) (Jaynes-Cummings/Dicke) (Cesium, F=4)

Congrès Général SFP 2019 – Nantes Alexandre Dareau

Looking for an experimental signature...

Our probe : fmuorescence spectroscopy

4

SPCM excitation beam local

• scillator

for ofg-resonant spin-motion coupling → yields trap frequencies

(transitions from ground state to fjrst excited motional states)

azimuthal (y) ~ 96 kHz radial (x) ~ 174 kHz axial (z) ~ 247 kHz beatnote central frequency (10 MHz)

heterodyne detection power spectral density (PSD) yields energy spectrum

Congrès Général SFP 2019 – Nantes Alexandre Dareau

Experimental signature of the spin-motion coupling !

5

• fg-resonant coupling

resonant coupling vacuum Rabi splitting →

motional state coupling Rabi frequency dressed states

Congrès Général SFP 2019 – Nantes Alexandre Dareau

Experimental signature of the spin-motion coupling !

Scanning across resonance

6

[Dareau et al., PRL 121, 253603 (2018)] Energy (kHz) Zeeman shift ΔE (kHz)

Power Spectral Density (a. u.)

1

Trap frequencies

fx = 149(2) kHz fy = 93(2) kHz fz = 243(5) kHz m

F

=

• 3

, n

x y z

= Ωx / ωx = 0.24(2) Ωy / ωy = 0.38(2)

Rabi frequency (for n=1)

Ωx = 2π × 35(1) kHz Ωy = 2π × 36(1) kHz

ultra-strong coupling !

mF = -4, nxyz = 0 mF = -4, ny = 1 mF = -4, nx = 1 mF = -4, nz = 1

+

[Schneeweiss et al., PRA 98, 021801(R) (2018)]

possible to increase coupling strength even further

(e.g. in optical lattices)

Congrès Général SFP 2019 – Nantes Alexandre Dareau

Tuning the coupling strength

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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

Congrès Général SFP 2019 – Nantes Alexandre Dareau

Conclusion & outlook

8 naturally present in nanofjber-based optical traps (& in optical microtraps) possible to tune with additional light fjeld analogy with CQED (Jaynes-Cummings / Dicke) Outlook : CQED

increase coupling strength

Dicke model (F=4 N=8 atoms) → Phase transition in the “mesoscopic” regime (N < ∞ ) ?

Outlook : tunability

increase coupling strength

“deep-strong coupling regime” (coupling > trap frequency)

dynamical tuning / quenches

Ω(t) with variation faster than trap

• scillation period.

Dynamical Casimir efgect ?

Ultra-strong spin-motion coupling

Note : also in optical lattices >> Schneeweiss et al., PRA 98, 021801(R) (2018)

Congrès Général SFP 2019 – Nantes Alexandre Dareau

Thank you for your attention !

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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

PRA 98, 021801(R) (2018) [arXiv:1706.07781]

Slides available on www.adphys.eu

@adphys

References :

• Y. Meng, A. Rauschenbeutel, P. Schneeweiss & AD