Abstract
Storage and retrieval of parametric down-conversion (PDC) photons are demonstrated with electromagnetically induced transparency (EIT). Extreme frequency filtering is performed for the THz order of broadband PDC light and the frequency bandwidth of the light is reduced to the MHz order. Storage and retrieval procedures are carried out for frequency-filtered PDC photons. Since the filtered bandwidth (full width at half-maximum (FWHM)=9 MHz) is within the EIT window (FWHM=12.6 MHz), the flux of the PDC light is successfully stored and retrieved. The nonclassicality of the retrieved light is confirmed by using the photon counting method, where the classical inequality that is only satisfied for classical light fields is introduced. Since PDC photons can be utilized for producing a single-photon state conditionally, storage and retrieval procedures are also performed for conditional single photons. The anticorrelation parameter used for checking the property of the single-photon state shows a value of less than 1, which means that the retrieved light is in a nonclassical region.
Highlights
Transferring a quantum state of light to an atomic ensemble enables us to implement quantum memory for photons [1, 2], generate a nonclassical state of an atomic ensemble, and manipulate a quantum state of light [3, 4, 5]
We reduced the bandwidth of the parametric down-conversion (PDC) photons from 10 THz to 9 MHz by using a filtering cavity (FC) [full width at half-maximum (FWHM) of the bandwidth = 9 MHz, free spectral range (FSR) = 1.5 GHz], an etalon (ET) [FWHM of the bandwidth = 300 MHz, FSR = 37 GHz], and a combination of a holographic grating (HG) and a polarization maintaining single mode fiber (PMF) [FWHM of the bandwidth = 23 GHz]
We have demonstrated storage and retrieval of PDC photons with electromagnetically induced transparency (EIT), where the bandwidth of the light was reduced from THz to MHz order
Summary
Transferring a quantum state of light to an atomic ensemble enables us to implement quantum memory for photons [1, 2], generate a nonclassical state of an atomic ensemble, and manipulate a quantum state of light [3, 4, 5]. Storage and retrieval of nonclassical light and generation of entanglement between two distant atomic ensembles have been demonstrated [7, 8, 9] In these experiments, Raman scattered photons generated from atomic ensembles were used as nonclassical light [10]. Raman scattered photons generated from atomic ensembles were used as nonclassical light [10] Another method of generating nonclassical light, the parametric down-conversion (PDC) process, has been widely used in fundamental experiments in quantum optics [11] and for demonstrating various quantum information protocols [12, 13]. We demonstrated storage and retrieval of PDC photons, where we avoided the problem on the bandwidth mismatch between PDC photons and EIT spectral width by using frequency filtering technique. We checked preservation of the single photon property through the storage process by using triggered PDC photons
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