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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Narrow linewidth photon pair generation from polarized warm atomic gas using hollow optical pumping

Taek Jeong, Han Seb Moon

Published Jun 1, 2017• 0 citations
Publisher

Abstract

Summary form only given. Entangled photon pair is key factor for realization of quantum communication, quantum information, etc. For long distance quantum communication, it is necessary to generate narrow band biphoton for interaction with atomic based quantum memory. In recent years, generation of time-frequency entangled photon pairs based on spontaneous four-wave mixing (SFWM) process in atomic ensemble have been reported [1-3]. Very recently, S. Chu et al. achieved generation of strongly correlated subnatural-linewidth biphoton from Doppler-broaden hot atomic ensemble [4]. The group used paraffin-coated87Rb vapour cell and separated optical pumping effect for reduce noise of fluorescence from resonant coupling field. In this paper, we performed experiment for subnatural-linewidth biphoton generation from hot atomic ensembles by using a hollow optical pumping field and regular vapour cell, which are not special coated cell.

DOI
10.1109/cleoe-eqec.2017.8087367

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Summary form only given. Entangled photon pair is key factor for realization of quantum communication, quantum information, etc. For long distance quantum communication, it is necessary to generate narrow band biphoton for interaction with atomic based quantum memory. In recent years, generation of time-frequency entangled photon pairs based on spontaneous four-wave mixing (SFWM) process in atomic ensemble have been reported [1-3]. Very recently, S. Chu et al. achieved generation of strongly correlated subnatural-linewidth biphoton from Doppler-broaden hot atomic ensemble [4]. The group used paraffin-coated87Rb vapour cell and separated optical pumping effect for reduce noise of fluorescence from resonant coupling field. In this paper, we performed experiment for subnatural-linewidth biphoton generation from hot atomic ensembles by using a hollow optical pumping field and regular vapour cell, which are not special coated cell.
Abstract Entangled photon pairs, termed as biphotons, have been the benchmark tool for experimental quantum optics. The quantum-network protocols based on photon–atom interfaces have stimulated a great demand for single photons with bandwidth comparable to or narrower than the atomic natural linewidth. In the past decade, laser-cooled atoms have often been used for producing such biphotons, but the apparatus is too large and complicated for engineering. Here we report the generation of subnatural-linewidth (<6 MHz) biphotons from a Doppler-broadened (530 MHz) hot atomic vapour cell. We use on-resonance spontaneous four-wave mixing in a hot paraffin-coated 87Rb vapour cell at 63 °C to produce biphotons with controllable bandwidth (1.9–3.2 MHz) and coherence time (47–94 ns). Our backward phase-matching scheme with spatially separated optical pumping is the key to suppress uncorrelated photons from resonance fluorescence. The result may lead towards miniature narrowband biphoton sources.
We report the generation of narrowband entangled photon pairs (biphotons) from a hot atomic vapor cell. Making use of backward spontaneous four-wave mixing with electromagnetically induced transparency (EIT), we produced subnatural-linewidth (1.9 MHz < 6 MHz) biphotons from a Doppler-broadened (0.5 GHz) hot (63 C) paraffin-coated rubidium 87 vapor cell. The biphoton coherence time is controable and can be tuned up to 100 ns by EIT. The uncorrelated photons from resonance Raman scattering are suppressed by a spatially separated and tailored optical pumping beam. The spectral brightness is as high as 14,000 s−1MHz−1. As compared with the cold-atom experiment , the hot atomic vapour cell configuration is much simpler for operation and maintenance, and it is a continuous biphoton source. Our demonstration may lead to miniature narrowband biphoton sources based on atomic vapour cells for practical quantum applications and engineering.
Orbital angular momentum (OAM) entangled photon pairs with narrow bandwidths play a crucial role in the interaction of light and quantum states of matter. In this article, we demonstrate an approach for generating OAM entangled photon pairs with a narrow bandwidth by using a single driving beam in a 85 Rb atomic vapor cell. This single driving beam is able to simultaneously couple two atomic transitions and directly generate OAM entangled biphotons by leveraging the OAM conservation law through the spontaneous four-wave mixing (SFWM) process. The photon pairs exhibit a maximum cross-correlation function value of 27.7 and a linewidth of 4 MHz. The OAM entanglement is confirmed through quantum state tomography, revealing a fidelity of 95.7% and a concurrence of 0.926 when compared to the maximally entangled state. Our scheme is notably simpler than previously proposed schemes and represents the first demonstration of generating subnatural-linewidth entangled photon pairs in hot atomic systems.
Biphotons and single photons with narrow bandwidths and long coherence times are essential to the realization of long-distance quantum communication (LDQC) and linear optical quantum computing (LOQC). In this Letter, we manipulate the biphoton wave functions of the spontaneous four-wave mixing in a two-level atomic ensemble with a single-laser pump scheme. Our innovative experimental approach enables the generation of biphotons with a sub-MHz bandwidth of 0.36 MHz, a record spectral brightness of 2.28×10^{7} s^{-1} mW^{-1} MHz^{-1}, and a temporally symmetric wave packet at moderate optical depth. The strong nonclassical cross-correlation of the biphotons also enables the observation of heralded sub-MHz-linewidth single photons with a pronounced single-photon nature. The generation of sub-MHz-linewidth biphotons and single photons with a two-level atomic ensemble not only finds applications in quantum repeaters and large cluster states for LDQC and LOQC but also opens up the opportunity to miniaturize the biphoton or single-photon sources for chip-scale quantum technologies.
The biphotons, or pairs of time-energy entangled photons, generated from a hot atomic vapor via the process of spontaneous four-wave mixing (SFWM) have the following merits: stable and tunable frequencies as well as linewidth. Such merits are very useful in the applications of long-distance quantum communication. However, the hot-atom SFWM biphoton sources previously had far lower values of generation rate per linewidth, i.e., spectral brightness, as compared with the sources of biphotons generated by the spontaneous parametric down conversion (SPDC) process. Here, we report a hot-atom SFWM source of 960-kHz biphotons with a generation rate of 3.7×\times× 10510^5105 pairs/s. The high generation rate, together with the narrow linewidth, results in a spectral brightness of 3.8×\times× 10510^5105 pairs/s/MHz, which is 17 times of the previous best SFWM result and also better than all known SPDC results. The all-copropagating scheme employed in our biphoton source is the key improvement, enabling the achieved spectral brightness to be about one quarter of the ultimate limit. Furthermore, this biphoton source had a signal-to-background ratio (SBR) of 2.7, which violated the Cauchy-Schwartz inequality for classical light by about two-fold. Although an increasing spectral brightness usually leads to a decreasing SBR, our systematic study indicates that both of the present spectral brightness and SBR can be further enhanced. This work demonstrates a significant advancement and provides useful knowledge in the quantum technology using photons.
Driven by the desire of narrow-band photon pairs source, in this Mphil thesis work, we demonstrate the generation of photon pairs with controllable coherence time up to 1.72 microseconds, using spontaneous four-wave mixing with electromagnetically induced transparency in a laser-cooled atomic ensemble with an optical depth (OD) as high as 130. At such a high OD, we find that the pump laser intensity profile has a significant effect on the time-frequency entangled two-photon waveform. We also confirm the quantum particle nature of heralded narrow-band single photons generated from this source.