Electromagnetically Induced Transparency from a Single Atom in Free Space

Abstract

In this letter, we report an absorption spectroscopy experiment and the observation of electromagnetically induced transparency from a single trapped atom. We focus a weak and narrowband Gaussian light beam onto an optically cooled 138 Ba + ion using a high numerical aperture lens. Extinction of this beam is observed with measured values of up to 1.3%. We demonstrate electromagnetically induced transparency of the ion by tuning a strong control beam over a two-photon resonance in a three-level Λ-type system. The probe beam extinction is inhibited by more than 75% due to population trapping.PACS numbers: 42.50. Gy, Atom-photon interfaces will be essential building blocks in future quantum networks [1,2]. Here, photons are usually adopted as the messengers due to their robustness in preserving quantum information during propagation, while atoms are used to store the information in stationary nodes. The efficient transfer of quantum information between atoms and photons is then essential and requires controlled photon absorption with a very high probability. The requisite strong coupling can be achieved, for example, using high finesse cavities [3][4][5] or large atomic ensembles [6,7], which are the most studied routes towards such goals.Coupling of radiation to a single atom in free space is generally considered to be weak, however, technological advances, as nowadays available with large aperture lenses [8] and mirrors [9], recently led to reconsider this point of view. Novel experiments demonstrated extinctions of about 10% from single Rubidium atoms [10], single molecules [11,12] and quantum dots [13]. More recently, a light phase shift of one degree was observed by tuning an off-resonant laser to a single Rubidium atom [14], and non-linear switching was demonstrated with a single molecule [15]. These experiments demonstrate first steps towards quantum optical logic gates and quantum memories with single atoms in free space.Long term and controlled storage of quantum information will likely require electromagnetically induced transparency (EIT). This technique is widely used to control the absorption of weak light pulses or single photons in atomic ensembles [7,16] and in high-finesse cavities [17]. Here, a two-photon Raman transition in lambda-type three-level atoms is driven by the weak probe light together with a strong control laser. The control laser leads to splitting of the excited state by the AC Stark effect, which suppresses the absorption of the resonant probe light. Consequently, the change of the control laser intensity can gate the propagating probe field between absorption and transmission. Furthermore, adiabatic switching of the control light can trigger the storage and retrieval of a probe photon onto and from the long-lived atomic ground states [1,18].So far, EIT has been a phenomenon specific to optically thick media consisting of ensembles of many atoms [18], where both the optical fields and the atomic states are modified. However, quantum information processing requires single well-define...

QED with a spherical mirror

“…Theory predicts that the best possible absorption between an incoming field and single atom arises when the incoming field matches the spatial atomic radiation mode [15,16]. Recent experiments have demonstrated substantial extinctions from single molecules [17][18][19], atoms [20,21] and quantum dots [22] in free space, thus showing the potential of free space coupling with high NA optics for fundamental investigation of light-matter interactions.The above mentioned studies make use of the interaction of real photon with single atoms. There has also been a rapid increase in the number of experiments related to Casimir forces between dielectric materials, which are the result of the modification of the mode density of virtual photons.…”

Light–matter interaction in free space

“…Such extinction measurements where performed in Refs. [17–21]. The achieved amount of extinction is listed in Table 1.…”

Time-resolved scattering of a single photon by a single atom

“…Strong light-matter interaction by using either large ensembles of atoms12 or single atoms inside cavities345 has received much attention in the past. More recently, significant light-matter interaction has also been observed between single quantum systems and weak coherent fields in free space67891011. The time-reversal symmetry of Schroedinger's and Maxwell's equations suggests that the conditions for perfect absorption of an incident single photon by a single atom in free space can be found from the reversed process, the spontaneous emission of a photon from an atom prepared in an excited state121314151617181920.…”