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Optics Express

Temporal- and spectral-property measurements of narrowband photon pairs from warm double-Λ-type atomic ensemble

Taek Jeong, Han Seb Moon

Published Jan 20, 2020• 22 citations
Publisher

Abstract

We investigate the temporal and spectral properties of narrowband photon pairs from a double-Λ-type atomic system of a warm 87Rb atomic ensemble. The temporal properties of the narrowband photons are investigated by measuring their auto-correlation and cross-correlation functions. The spectral measurement of the photon pair is obtained by applying the stimulated emission method. We show that the biphoton spectral waveform with a spectral width of ∼6 MHz corresponds to the biphoton temporal waveform with a temporal width of ∼26 ns. We believe that our results can contribute to the characterization of narrowband photons generated from atomic ensembles and aid in the development of new photonic quantum states generated from atomic systems.

DOI
10.1364/oe.385896

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We investigate the temporal and spectral properties of narrowband photon pairs from a double-Λ-type atomic system of a warm 87Rb atomic ensemble. The temporal properties of the narrowband photons are investigated by measuring their auto-correlation and cross-correlation functions. The spectral measurement of the photon pair is obtained by applying the stimulated emission method. We show that the biphoton spectral waveform with a spectral width of ∼6 MHz corresponds to the biphoton temporal waveform with a temporal width of ∼26 ns. We believe that our results can contribute to the characterization of narrowband photons generated from atomic ensembles and aid in the development of new photonic quantum states generated from atomic systems.
Photon-pair sources from atomic ensembles are considered essential to the development of quantum science and technology based on atom-photon interfaces. The measurement of spectral-temporal biphoton wave forms is important for the characterization of frequency-time entangled photon pairs. Here, we demonstrate a stimulated measurement of the biphoton spectral wave form (BSW) of narrow-band photon pairs emitted from a Doppler-broadened cascade-type atomic ensemble. A BSW with submegahertz resolution is obtained as a function of the absolute optical frequency determined by atomic transitions, which reveals a spectral shift of approximately 510 MHz from the expected resonance frequency of the $5{P}_{3/2}\ensuremath{-}5{D}_{5/2}$ and $5{S}_{1/2}\ensuremath{-}5{P}_{3/2}$ transitions of 87Rb^{87}\mathrm{Rb}87Rb atoms.
Abstract We investigate the spectral–temporal biphoton waveforms of the photon pairs emitted from cascade-type two-photon-coherent warm 87Rb atoms via the spontaneous four-wave mixing process in the 5S1/2–5P3/2–5D5/2 transition, under the condition of the different detuning frequencies (symmetric detuning conditions of ± 1 GHz) of the pump and coupling lasers relative to the 5P3/2 state. In both detuning cases corresponding to ± 1 GHz, the biphoton temporal waveforms and biphoton spectral waveforms of the photon pairs are measured by means of time-resolved coincidence photon counting and stimulated measurements, respectively. Although photon-pairs were generated using opposite detunings, we confirm that the spectral–temporal biphoton waveforms of the photon pairs are very similar. Furthermore, we observe Hong–Ou–Mandel interference with 82% visibility with the two independent heralded single photons.
Photonic quantum states generated from atomic systems play prominent roles in long-distance quantum networks and scalable quantum communication, because entangled photon pairs from atomic ensembles possess a universal identity and narrow spectral bandwidth for quantum repeaters. In this study, we propose and demonstrate a novel, to the best of our knowledge, method for the joint spectral intensity measurement of narrowband continuous wave (CW)-mode photon pairs from a warm atomic ensemble using stimulated emission and beat interferometry for the first time. Our approach offers the advantage of sub-megahertz resolution, absolute optical frequency measurements with megahertz-level accuracy, fast collection time, and high signal-to-noise ratio; thus, our method can find important applications in the characterization of narrowband photon pairs generated from sources including atoms and artificially structured material.
Abstract Photonic quantum states generated from atomic ensembles will play important roles in future quantum networks and long-distance quantum communication because their advantages, such as universal identity and narrow spectral bandwidth, are essential for quantum nodes and quantum repeaters based on atomic ensembles. In this study, we report the collectively coherent superposition of biphoton wavefunction emitted from different velocity classes in a Doppler-broadened cascade-type atomic ensemble. We experimentally demonstrate that the three times difference of temporal width of both biphoton temporal waveforms varies dependent on the wavelengths of the signal and idler photons from both 6S1/2–6P3/2–6D5/2 and –8S1/2 transitions of 133Cs, corresponding to the idler and signal wavelengths of 852 nm–917 nm and 852 nm–795 nm, respectively. Our results help understand the characteristics of biphoton sources from a warm atomic ensemble and can be applied to long-distance quantum networks and practical quantum repeaters based on atom–photon interactions.
Telecom band photonic quantum states generated from atomic systems are critical quantum resources for long‐distance and scalable quantum communication networks. Here, the beat phenomenon in the autocorrelation function of the telecom‐wavelength photon due to the velocity‐selective classes of the atoms in a Doppler‐broadened atomic ensemble of the cascade‐type 5S1/2–5P3/2–4D5/2 transition of 87Rb is reported. Although the signal (1529 nm) and idler (780 nm) photons are emitted from a single‐atomic ensemble, the autocorrelation functions of the signal and idler photons exhibit significantly different features, with temporal widths of 7 and 0.13 ns, respectively. Furthermore, the biphoton spectral waveform of the telecom band photon pair is measured using a stimulated emission method. The biphoton waveforms of the telecom‐wavelength biphoton source demonstrate good agreement with the magnitude of the Fourier components of the measured biphoton temporal and spectral waveforms.
We report on theoretical and experimental investigations of time-resolved cross- and auto-correlation measurements of spectrally narrowband photon pairs generated in sources based on parametric down conversion in resonant waveguide structures. We show that time-resolved measurements provide detailed and useful information about the spectral and modal structure of the bi-photon state. The shape of the cross-correlation function is asymmetric with exponential decays determined by the lifetimes of the signal and idler photons in the cavity. The time-resolved auto-correlation has Lorentzian shape. The measured value convoluted with the detector windows and mode beating can be used to characterise the spectral longitudinal mode behaviour. The temporal width of the auto-correlation function is more than two times longer that the cross-correlation time. This reveals that the spectral bandwidth of the single-photon component is much broader than the spectral width of the two-photon component.