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Journal of Physics B Atomic Molecular and Optical Physics

Nonlinear particle interaction effects on Ramsey interferometry in an atom–heteronuclear molecule conversion system

Sheng-Chang Li

Published Oct 4, 2010• 7 citations
Publisher

Abstract

We investigate the Ramsey interferometry with a nonlinear atom–heteronuclear molecule conversion boson system, where the nonlinearity arises from the interaction between coherent atoms. In this coupled system, the nonlinear interaction between particles plays a significant role in a dynamic process. The nice Ramsey-type interference fringes in the time domain have been obtained when a sequence of two identical magnetic field pulses near the Feshbach resonance is applied. We show that a blue shift (or a red shift) of frequency of Ramsey-type fringes emerges due to the repulsive particle interaction (or the attractive particle interaction). In particular, we find that the visibility of Ramsey-type patterns can be strongly modified by the nonlinear particle interaction and a much higher visibility of Ramsey-type fringes can be accessed by tuning the Ramsey pulse duration appropriately.

DOI
10.1088/0953-4075/43/20/205303

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We investigate the Ramsey interferometry with a nonlinear atom–heteronuclear molecule conversion boson system, where the nonlinearity arises from the interaction between coherent atoms. In this coupled system, the nonlinear interaction between particles plays a significant role in a dynamic process. The nice Ramsey-type interference fringes in the time domain have been obtained when a sequence of two identical magnetic field pulses near the Feshbach resonance is applied. We show that a blue shift (or a red shift) of frequency of Ramsey-type fringes emerges due to the repulsive particle interaction (or the attractive particle interaction). In particular, we find that the visibility of Ramsey-type patterns can be strongly modified by the nonlinear particle interaction and a much higher visibility of Ramsey-type fringes can be accessed by tuning the Ramsey pulse duration appropriately.
We propose a feasible scheme to realize nonlinear Ramsey interferometry with a two-component Bose-Einstein condensate, where the nonlinearity arises from the interaction between coherent atoms. In our scheme, two Rosen-Zener pulses are separated by an intermediate holding period of variable duration and through varying the holding period we have observed nice Ramsey interference patterns in the time domain. In contrast to the standard Ramsey fringes our nonlinear Ramsey patterns display diversiform structures ascribed to the interplay of the nonlinearity and asymmetry. In particular, we find that the frequency of the nonlinear Ramsey fringes exactly reflects the strength of nonlinearity as well as the asymmetry of system. Our finding suggests a potential application of the nonlinear Ramsey interferometry in calibrating the atomic parameters such as scattering length and energy spectrum.
We discuss the frequency and visibility of atom-molecule Ramsey fringes observed in recent experiments by Claussen et al. [Phys. Rev. A 67, 060701 (2003)]. In these experiments a 85Rb^{85}\mathrm{Rb}85Rb Bose-Einstein condensate was exposed to a sequence of magnetic field pulses on the high-field side of the 155G155\phantom{\rule{0.3em}{0ex}}\mathrm{G}155G Feshbach resonance. The observed oscillation frequencies largely agree with the theoretically predicted magnetic field dependence of the binding energy of the highest excited diatomic vibrational state, except for a small region very close to the singularity of the scattering length. Our analytic treatment of the experiment, as well as our dynamical simulations, follow the magnitude of the measured oscillation frequencies as well as the visibilities of the Ramsey fringes. We show that significant deviations from a purely binary dynamics, with an associated binding frequency, occur when the spatial extent of the molecular wave function becomes comparable with the mean distance between the atoms in the dilute gas. The experiments thus clearly identify the conditions under which diatomic molecules may be identified as a separate entity of the gas or, conversely, when the concept of binary physics in a many-body environment is bound to break down.
Taking Rosen-Zener tunneling as the underlying process，a scheme to achieve nonlinear Ramsey interferometry with a two-component trapped Bose-Einstein condensate is proposed. Abundant nonlinear Ramsey interference fringes are observed in time domain by the numerical simulations and these fringes are very different from the sinusoidal pattern for linear Ramsey interference due to the dominant nonlinear interaction between atoms. Furthermore，Fourier transformation results show that the fundamental frequency of Ramsey fringes can exactly reflect the information of nonlinearity or asymmetry. This finding provides an opportunity to measure atomic properties via measuring the frequency of fringes.
We investigate the nonlinear Ramsey interferometry of a bosonic Josephson junction coupled to an optical cavity by applying two identical pumping field pulses separated by a holding field in the time domain. When the holding field is absent, we show that the atomic Ramsey fringes are sensitive to both the cavity-pump detuning and the initial state, and their periods can encode the information on both the atom-field coupling and the atom-atom interaction. For a weak holding field, we find that the fringes characterized by the oscillation of the intra-cavity photon number can completely reflect the frequency information of the atomic interference due to the weak atom-cavity coupling. This finding allows a nondestructive observation of the atomic Ramsey fringes via the cavity transmission spectra.
Summary form only given. The field of atom interferometry is experiencing rapid progress. Atom interferometers have been used to determine topological phase shifts such as the Aharonov-Bohm or Aharonov-Casher effects. Both two beam and more recently multiple beam atom interferometers have been realized. We report on an investigation of the electric (or scalar) Aharonov-Bohm effect in a multiple beam Ramsey experiment. The topological phase shift leads to collapse and revival of the fringe pattern. In a first interaction region cesium atoms are optically pumped into a dark coherent superposition of the magnetic quantum numbers m/sub F/=-4, -2, 0, 2 and 4 of the 6S/sub 1/2/ (F=4) ground state. The coherent superposition is probed after a time T in a second interaction region. When the atoms are irradiated in between the Ramsey interactions by an additional linearly polarized light field 400 MHz blue detuned to the F=4/spl rarr/F'=4 transition of the cesium D1 line, the induced AC Stark shift increases quadratically with the magnetic quantum number. The laser field coupling to the induced atomic dipole moment causes-in the absence of any classical forces-an electric Aharonov-Bohm phase shift.
Ramsey interferometry as one of the most important high-precision measurement methods has prospects for inferring various properties of ultracold atoms and molecules. We investigate the multi-pulse Ramsey interferometry of a double-well Bose–Einstein condensate (BEC) in an optical cavity. Compared with the standard two-pulse Ramsey scheme, our multi-pulse Ramsey proposal greatly relaxes the requirements for both intensity and width of the pulses, allowing the interferometry to be achieved using weak and narrow pulses. When the pumping pulses characterizing the coupling between the cavity field and the atomic BEC are applied to the zero background field, we demonstrate the atomic Ramsey fringes in the time domain for different pulse numbers and different pulse widths. We find that although the multi-pulse Ramsey fringes are no longer sensitive to cavity-pump detuning, they can still record the information of the interaction between coherent atoms. We obtain the fundamental frequency of the multi-pulse Ramsey fringes analytically and find that it is proportional to the number of pulses. Particularly, it is shown that the minimum of the fundamental frequency is exactly the critical point of the phase transition of the system. For a nonzero background field, the results indicate that a nondestructive observation of atomic Ramsey fringes by cavity transmission spectroscopy is feasible. Our findings provide insights for improving the accuracy of Ramsey interferometry and for using interferometry to observe phase transitions.