Abstract
The paper reports on the optical detection and spectroscopy of ultracold atoms near a gold surface. A probe light field is used to excite surface plasmon polaritons. The refractive index of the atomic gas shifts the plasmon resonance and changes the reflected light power. Thus, the sensitivity of the detection is plasmonically enhanced. Absorption of photons from the evanescent wave is avoided by detuning the laser from atomic resonance which makes the detection scheme potentially nondestructive. The spectrum of the signal is determined by a Fano resonance. We show that atoms can be detected nondestructively with single atom resolution for typical parameters in cold atom experiments. Thus, the method is suitable for quantum nondemolition measurements of matter wave amplitudes. Experimentally, we measure a technically-limited sensitivity of 30 atoms and extend the detection scheme to dispersively image the atom cloud near the surface.
Highlights
A quantum nondemolition (QND) measurement determines one of two conjugate variables of a quantum object with arbitrary precision
As proposed in Refs. [3,4], evanescent waves can in principle be used for the QND measurement of the amplitude of a matter wave that is reflected at the surface, which is equivalent to the nondestructive measurement of the atom number with single atom precision
The paper presents a sensitive method for the dispersive detection of ultracold atoms at submicron distance from solid surfaces using plasmonically enhanced evanescent waves
Summary
A quantum nondemolition (QND) measurement determines one of two conjugate variables of a quantum object with arbitrary precision. We note in this context that compared to the plane surface case much stronger absorptive and dispersive light matter interactions can been obtained by positioning cold atoms close to nanoscale devices as nanofibers [24,25], whispering gallery mode microresonators [26], and photonic crystal waveguides [27], and single atom detection has been demonstrated in those and similar systems Another extremely sensitive spectroscopy method which allowed for the detection of atomic quadrupole transitions was demonstrated by probing an atomic vapor with plasmonic nanostructures in selective reflection [28]. It demonstrates that the detection scheme can be used to dispersively image the atom cloud
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