Abstract
We present experimental observations of interference between an atomic spin coherence and an optical field in a Λ-type gradient echo memory. The interference is mediated by a strong classical field that couples a weak probe field to the atomic coherence through a resonant Raman transition. Interference can be observed between a prepared spin coherence and another propagating optical field, or between multiple Λ transitions driving a single-spin coherence. Our scheme can behave as a controllable time-delayed beamsplitter with dynamically tuneable splitting ratio and allows, in principle, for unity interference visibility.
Highlights
We present experimental observations of interference between an atomic spin coherence and an optical field in a Λ-type gradient echo memory
A two-photon transition between hyperfine states can be used to manipulate the atomic state in a coherent manner. Examples of this include stimulated Raman adiabatic passage (STIRAP) [1], electromagnetically induced transparency (EIT) [2, 3] and photon echoes [4], all of which have been proposed as central elements in a range of protocols for storing and processing optical quantum information
Experimental observation of interference between backward-propagating stimulated photon echoes has been reported [4], where two echoes have been selectively chosen in time to destructively interfere while the information contained in the suppressed echo was not recovered from the sample
Summary
This scheme has the capacity to arbitrarily access stored bits of information [8] and manipulated the stored information in the time and frequency domains [11]. The normal mode of the twolevel GEM is defined as ψ(t, k) = kE(t, k) + N σ12(t, k) [12] and propagates in the (t, k) plane where N is the linear atomic density. Like the normal mode in EIT[3], ψ(t, k) is a combination of atomic polarisation and optical field and can be considered a polariton. The velocity at which the polariton propagates in k-space is proportional to the atomic frequency gradient and, by switching the sign of the magnetic field gradient, the evolution of the polariton can be reversed. When the polariton again reaches k = 0 the atomic coherence is rephased and the polariton is recalled as an optical field
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