Entanglement-preserving frequency conversion in cold atoms

Abstract

We propose a method that enables efficient frequency conversion of quantum information based on recently demonstrated strong parametric coupling between two single-photon pulses propagating in a slow-light atomic medium at different group velocities. We show that an incoming singlephoton state is efficiently converted into another optical mode in a lossless and shape-conserving manner. The persistence of initial quantum coherence and entanglement within frequency conversion is also demonstrated. We first illustrate this result for the case of small frequency difference of converted photons, and then discuss the modified scheme for conversion of photon wavelengths in different spectral ranges. Finally we analyze the generation of a narrow-band single-photon frequency-entangled state.

Frequency conversion and entanglement in V configuration atomic ensemble

“…The quantum fields couple to the dipole-allowed transitions jai $ jbi and jci $ jbi, respectively, while the transition jai $ jci is electric-dipole forbidden. In [23][24][25], they believe that the classical transition jai $ jci can be induced by applying a strong magnetic field for a magnetic-dipole-allowed transition or by applying an electric quadrupole transition. However, the magnetic-dipole-allowed transition and electric quadrupole transition are much weaker than electric-dipole, therefore, here we use a two-photon Raman transition via a fourth level jdi [26] to realize the classical transition jai $ jci.…”

“…Recently, Gogyan and Malakyan [23] proposed a protocol of frequency conversion in atomic ensembles which can avoid losses and shape distortion in V-type atomic configuration. In stead of using the propagation equation, we employ polariton technique to show the efficiency of frequency conversion (EFC) and entanglement of the two-mode fields in V configuration atomic ensemble.…”

Coherent Conversion Between Microwave and Optical Photons—An Overview of Physical Implementations

“…Ensembles of cold trapped Rydberg atoms also exhibit a useful level structure, large dipole moments, and a giant electro‐optic effect, allowing microwave‐to‐optical conversion . Specific proposals have been made for caesium, rubidium, (Figure c,d) and ytterbium gases to be used, with several pumps coupling multiple transitions allowing an appropriate signal and output wavelength to be selected. Collective states in a gas of Rb have been strongly coupled to superconducting transmission line cavities and up‐conversion was first demonstrated using Rydberg states in Rb.…”

Single-photon frequency conversion in nonlinear crystals

“…Bragg scattering in nonlinear fibers or FWM in atomic gases) as demonstrated for weak coherent fields [18,19] and heralded single photons [20,21]. We mention that the use of atomic ensembles as nonlinear media for single-photon frequency conversion is also being discussed [22,23], and has been experimentally demonstrated [21]. This latter approach offers a smaller bandwidth compared with nonlinear crystals, but also a better perspective for achieving coherent control [24].…”