MICRA Misure Interferometriche di forze a Corto Range

MICRA Misure Interferometriche di forze a Corto Range con reticoli Atomici Obiettivo del progetto: - Studio della forza superficie-atomo su scala micrometrica mediante tecniche interferometriche divenute recentemente disponibili in fisica dei gas atomici degeneri intrappolati. - La componente dominante della forza nel range di distanze di 5 -10 micron e’ data dal termine di Casimir-Polder, nonché dalle fluttuazioni termiche del campo elettromagnetico. - La verifica e il controllo sperimentale di queste forze sono condizione necessaria per migliorare i limiti di conoscenza su forze non-newtoniane.

Partecipanti FIRENZE Massimo Inguscio (resp nazionale) PO 70% Giovanni Modugno (resp locale) PA 70% Giacomo Roati Ass. Ric. Chiara Fort Ric 30% Francesco Minardi Ric 20% Leonardo Fallani Ass. Ric. 30% Matteo Zaccanti Dott. 100% TRENTO Sandro Stringari (resp locale) PO 40% Lev Pitaevskii PO 20% Iacopo Carusotto Ric 30% Mauro Antezza Dott. 60%

MICRA: struttura del progetto -Firenze progettazione e realizzazione dell’esperimento -Trento teoria della forza superficie-atomo e dinamica dei gas ultrafreddi -Durata del progetto: 3 anni R&D: SQUAT-Super (LNS-Catania + Firenze) (superfici e interazioni) Collaborazione col JILA, Boulder-Colorado (E. Cornell).

Degenerate gases temperature Fermions Bosons TT<<TTCF EF

Atomic quantum gases __________________________________ G. Modugno, G. Ferrari, G. Roati, R. Brecha, A. Simoni, and M. Inguscio Science 294, 1320 (2001) G. Roati , F. Riboli, G. Modugno, M. Inguscio Phys. Rev. Lett. 89, 150403 (2002).

OPTICAL TRAPS (Dipole force) red detuning blue detuning

Excitation of Bloch oscillations in atomic Fermi gases - atomic gas initially feels 3 D harmonic trap+ gravity + periodic confinement - at t=0 one switches off harmonic trap System feels periodic potential + gravity and starts oscillating (Bloch oscillation). - After given evolution time the periodic potential is switched off. Atomic gas falls down, expands and is hence imaged. - Imaged profiles are proportional to initial momentum distribution

Atom interferometry in an optical lattice Wannier-Stark states in a lattice tilted by gravity: Their interference oscillates: Semiclassical picture: Bloch oscillations -q. B q +q. B

Bloch oscillations with fermions g Bloch oscillations of 40 K fermions trapped in a vertical optical lattice in presence of gravity G. Roati, E. De Mirandes, F. Ferlaino, H. Ott, G. Modugno, M. Inguscio Phys. Rev. Lett. 92, 230402 (2004)

Images of spin polarized Fermi gas performing Bloch oscillation Bloch frequency measured with precision in this experiment

Decoherence: Fermi vs Bose __________________________________ 107 4 1/2 4 Destabilization time can be estimated in terms of scattering length 4 1/2 G. Roati, E. De Mirandes, F. Ferlaino, H. Ott, G. Modugno, M. Inguscio Phys. Rev. Lett. 92, 230402 (2004)

THEORY vs EXPERIMENT I. Carusotto, L. Pitaevskii, S. Stringari, G. Modugno, M. Inguscio cond-mat/0503141 Phys. Rev. Lett. (2005) in press

Bloch oscillations as a sensitive probe of forces at short range Features: ü high resolution in presence of gravity ü direct measurement of forces ü low sensitivity to gradients ü high sensitivity (10 -7 g) thermal asymp. force + point like approx. Calculated Bloch frequency shift with respect to unperturbed value full calculation Carusotto, L. Pitaevskii, S. Stringari, G. Modugno, M. Inguscio, Phys. Rev. Lett. 95, 093202 (2005).

Casimir-Polder and thermal force - Behaviour of Casimir-Polder force well explored experimentally at short distances (mainly forces between metallic bodies) (Bressi et al. 2002) - Behaviour at larger distances (few microns) less explored. In particular thermal effects of the force - Cold atoms are natural candidates to explore thermal effects of the force at moderately large distances (5 -10 microns), important also for exotic forces. - Previous experiments with cold atoms: Hinds (93), Aspect (97), Shimizu (01, 05), Vuletic (04), Cornell (05)

Casimir-Polder and thermal force Radiation from the substrate Radiation from environment - Force includes zero-point fluctuations effects (including relativistic retardation terms) + thermal radiation effects (crucial at large distance)

Asymptotic behaviour of the surface-atom force Casimir Polder thermal (Lifshitz) van der Waals Lifshitz Recent theoretical prediction out of thermal equilibrium (Antezza, Pitaevskii, Stringari, PRL 95, 113202 (2005)) surface environment Casimir-Polder

Vertical position (mm) Calculations of the frequency shift of the center-of-mass oscillations of the |1> condensate as a function of the number of atoms N 2 remaining in |2>. Time (w 2 -1)

Latest experiment with cold atoms First experimental attempt to measure Casimir force at thermal distances: Eric Cornell team at Boulder (Harber et al. Phys. Rev. A 72, 033610 (2005)

Casimir-Polder force from fused silica surface van der Waals Exp at 300 K: Harber et al. , Phys. Rev. A 72, 033610 (2005) Theory: Antezza, Pitaevskii, Stringari, Phys. Rev A 70, 053619 (2004)

Limits on newtonian forces Harber et al. , Phys. Rev. A 72, 033610 (2005)

Preliminary measurement of thermal effects JILA

Bloch oscillations in and out of thermal equilibrium Non equilibrium T=300 K T=0 K Trento theory MICRA

Control of Casimir-Polder force (change of sign)

A Rb BEC in a K Fermi sea __________________________________ NF = 104 TF = 250 n. K NB = 2 104 TC= 110 n. K Good thermal contact: Tmin= 80 n. K = 0. 3 TF G. Roati , F. Riboli, G. Modugno, M. Inguscio Phys. Rev. Lett. 89, 150403 (2002).

MICRA: key ideas for the experiment Carbon surface + heating laser Magnetic manipulation of the sample Alternating dense metal stripes Cold finger for cryogenic cooling + dielectric Casimir screen Narrow-band, high stability infrared laser reflected off the surface Features: ü magnetic manipulation of samples close to surfaces ü surface heating-cooling capabilities ü alternating metals for improved sensitivity to gravity

MICRA: multiple approaches in one apparatus Bloch oscillations of fermions: sensitive to forces Dipole oscillations of Bose-Einstein condensates: sensitive to gradient of forces Interferometry with two condensates (MIT): sensitive to potentials

MICRA: new strategies Interferometry with a Bose-Einstein condensate with interactions tunable to zero Bose-Einstein condensation of bosonic potassium atoms, Science, 294, 1320 (2001)

MICRA: a new experiment for atom-surface force measurements Features: ü both Fermi and Bose atomic gases for maximum versatility ü high-quality dielectric surfaces under vacuum ü possibility of changing the surface and environment temperatures ü improved stability of the optical lattice to reach 10 -7 g sensitivity Expected results: ü high precision measurement of Casimir-Polder force including new thermal effects in 5 -10 micron range ü realistic perspectives for improved non-Newtonian short range force limits ü long term perspectives: test of the equivalence principle

Non-newtonian forces __________________________________ 10 -7 g 10 -10 g S. Dimopulos and A. A. Geraci, Phys. Rev. D 68, 124021 (2003)

Previsione di spesa (k€) I anno II anno Costruzione apparato (apparato da vuoto, sistemi laser, ottiche) 245 50 Strumentazione elettronica: generatori rf e microonde, sistemi di gestione esperimento (inventariabile) 31 60 20 111 Ottiche, elettronica, campioni, materiale da vuoto (consumo) 10 50 40 100 5 5 10 25 25 71 Spese di calcolo Missioni nazionali ed estere Totale 21 III anno 295 587