Collapses and revivals of stored orbital angular momentum of light in a cold-atom ensemble

Abstract

We report on the storage of orbital angular momentum of light in a cold ensemble of cesium atoms. We employ Bragg diffraction to retrieve the stored optical information impressed into the atomic coherence by the incident light fields. The stored information can be manipulated by an applied magnetic field and we were able to observe collapses and revivals due to the rotation of the stored atomic Zeeman coherence for times longer than 15 µs. PACS numbers: 42.50.Gy, 42.50.Ex, 42.50.Va Light beams carrying orbital angular momentum (OAM) have attracted an enormous recent interest owing to the possibility of encoding quantum information in a multidimensional state space [1], to their use to excite vortices in Bose-Einstein condensates [2], as well as to a number of others interesting applications [3]. One important family of these beams, the Laguerre-Gaussian (LG) modes of the electromagnetic field [4], possesses wave-fronts dislocation or vortices specified by a topological charge m, which sets its OAM along the propagation direction as being equal to mh per photon. The coherent and nonlinear interaction of light beams carrying OAM with atomic systems have been reported previously using different experimental schemes [5,6,7,8,9]. From the perspective of quantum information processing, the use of multidimensional state space has a promising prospect to achieve higher quantum efficiency [10]. Indeed, entanglement between photons with OAM and a cold atomic ensemble was already reported in [11] and more recently the generation of twin light beams with OAM was achieved via four-wave mixing in a hot atomic vapor [12].However, further development in this field is strongly conditioned to our capability of reversibly store and manipulate these higher dimensional quantum states of light into long-lived atomic coherences. The light storage (LS) in an electromagnetically induced transparency (EIT) medium [13], which allow us to obtain later information of a previously stored light pulse, is a well understood phenomenon and was originally described in terms of a mixed two component light-matter excitation, called dark state polariton [14]. However, in a simpler alternative picture, LS can be described as being due to the creation of a ground state coherence grating which contains information on the amplitude and phase of an optical field and which survives after the switching off of the incident fields. To date, several experimental observations of this phenomenon were realized in different systems [15,16,17,18,19,20]. Recent theoretical and experimental work have also addressed the storage of spatial structures of light beams (images) in atomic vapors [21,22,23,24]. For instance, a light vortex was stored in a hot vapor for hundreds of microseconds and its robustness against diffusion demonstrated [21]. However, to date the storage and manipulation of superpositions of OAM states into an atomic ensemble, as well as the characterization of the retrieved states, has not yet been achieved.In this work, we report the storage of su...

Toward high-dimensional-state quantum memory in a cold atomic ensemble

“…After the seeding work of storing a light-carrying OAM in an atomic ensemble was reported by Moretti et al in Ref. [15], many groups and researchers are active in storing light encoded using a high-dimensional space. Although some work has been reported for light-carrying OAM or spatial structures in different physical systems, such works involve intense light sources [16][17][18][19][20][21][22][23].…”

Off-axis retrieval of orbital angular momentum of light stored in cold atoms

“…The theoretical analysis is based on a previous work [19], which showed that the retrieved field originates from the diffraction of the reading beam into the Zeeman coherence grating and is determined by the optical coherence [10,19], which in the low intensity limit is given by:…”

Nonlinear coupling between two Zeeman coherence gratings stored in cold atoms

“…Indeed, EIT-based memories have been used to store complex transverse spatial light profiles (images) [12,13], as well as states of orbital angular momentum of light [14,15]. Complex spatial modes and images have also been stored using the GEM technique [16].…”