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Time-resolved correlation engineering in DLCZ Raman photon sources
Authors:
Jiun-Shiuan Shiu,
Chang-Wei Lin,
Chi-Ming Yang,
Ite A. Yu,
Yong-Fan Chen
Abstract:
Memory-assisted quantum networks require photon sources with controllable temporal and correlation properties. The Duan-Lukin-Cirac-Zoller (DLCZ) protocol provides a platform based on spontaneous Raman scattering in atomic ensembles, but a unified predictive theory connecting control parameters to correlations under realistic propagation and noise conditions remains lacking. Here we present a prop…
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Memory-assisted quantum networks require photon sources with controllable temporal and correlation properties. The Duan-Lukin-Cirac-Zoller (DLCZ) protocol provides a platform based on spontaneous Raman scattering in atomic ensembles, but a unified predictive theory connecting control parameters to correlations under realistic propagation and noise conditions remains lacking. Here we present a propagation-inclusive open-system quantum theory that retains write-induced population redistribution while combining Heisenberg-Langevin dynamics with Maxwell-Schrödinger propagation. We experimentally validate its key predictions. The theory predicts time-dependent Stokes generation, spin-wave evolution, retrieved anti-Stokes wavepackets, and time-resolved cross-correlations. Experiments confirm robust correlations under retrieval tuning and enhanced correlations for shorter write pulses, consistent with the different scaling of correlated coincidences and accidental backgrounds with the mean spin-wave excitation number. Classically controlled retrieval enables temporal gating and slicing of the anti-Stokes wavepacket, establishing a quantitative framework for correlation engineering in memory-compatible DLCZ photon sources.
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Submitted 13 August, 2026;
originally announced August 2026.
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Photon pair antibunching and second-order correlations between pair events
Authors:
Chien-Chang Chen,
Ite A. Yu,
Hsi-Sheng Goan
Abstract:
We introduce the pair second-order correlation function $g_{\textrm{pairs}}^{\left(2\right)}=\left\langle \left(P^{\dagger}\right)^{2}P^{2}\right\rangle /\left\langle P^{\dagger}P\right\rangle ^{2}$, defined through the pair operator $P^{\dagger}=a^{\dagger}b^{\dagger}$, to characterize second-order correlations and pair bunching and antibunching in photon-pair creation processes. This quantity di…
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We introduce the pair second-order correlation function $g_{\textrm{pairs}}^{\left(2\right)}=\left\langle \left(P^{\dagger}\right)^{2}P^{2}\right\rangle /\left\langle P^{\dagger}P\right\rangle ^{2}$, defined through the pair operator $P^{\dagger}=a^{\dagger}b^{\dagger}$, to characterize second-order correlations and pair bunching and antibunching in photon-pair creation processes. This quantity directly probes correlations between pair-generation events within a single two-mode quantum state, providing access to the intrinsic pair-generation process beyond conventional single-mode or heralded second-order correlations, which do not directly capture correlations between pair events. Values of $g_{\textrm{pairs}}^{\left(2\right)}$ greater than, equal to, or less than unity correspond respectively to pair bunching, Poissonian pair statistics, and pair antibunching. Using the Cauchy--Schwarz inequality, we further show that all classical two-mode fields described by a positive Glauber--Sudarshan \ensuremath{P}-function satisfy $g_{\textrm{pairs}}^{\left(2\right)}\geq1$, so that pair antibunching is classically forbidden and constitutes an unambiguous signature of nonclassicality. We evaluate $g_{\textrm{pairs}}^{\left(2\right)}$ for several representative quantum states and show, in particular, that even arbitrarily weak two-mode squeezed vacuum states exhibit pair bunching. Comparison with heralded second-order correlations highlights the complementary information provided by these observables. The proposed correlation function is experimentally accessible via standard coincidence measurements, requires no phase reference or state reconstruction, and remains invariant under uniform loss.
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Submitted 26 July, 2026;
originally announced July 2026.
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Inhomogeneous mass trap for dark-state polaritons in atomic media
Authors:
Ding-An Chen,
Kai-You Huang,
Chun-Yen Hsu,
Meng-Cheng Xie,
Ite A. Yu,
Wen-Te Liao
Abstract:
The generation of a trapping potential for dark-state polaritons in a two-dimensional electromagnetically induced transparency system is theoretically studied. We show that such a trap can arise from a spatially inhomogeneous effective mass of the dark-state polariton. Because this mass inhomogeneity can be engineered by tuning the parameters of the control fields, the motion, spatial profile, and…
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The generation of a trapping potential for dark-state polaritons in a two-dimensional electromagnetically induced transparency system is theoretically studied. We show that such a trap can arise from a spatially inhomogeneous effective mass of the dark-state polariton. Because this mass inhomogeneity can be engineered by tuning the parameters of the control fields, the motion, spatial profile, and coherent behavior of bound dark-state polaritons can be tailored accordingly. Our results enable spatial controls of optical information and provide a possible route toward realizing Bose-Einstein condensation of dark-state polaritons in a trapping potential.
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Submitted 18 March, 2026;
originally announced March 2026.
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Temporally-long C-band heralded single photons generated from hot atoms
Authors:
Pei-Yu Tu,
Chia-Yu Hsu,
Wei-Kai Huang,
Tse-Yu Lin,
Chih-Sung Chuu,
Ite A. Yu
Abstract:
C-band photons are recognized for having the lowest loss coefficient in optical fibers, making them highly favorable for optical fiber-based communication. In this study, we systematically investigated the temporal width of C-band heralded single photons and developed a theoretical model for biphoton generation via the spontaneous four-wave mixing (SFWM) process using a diamond-type transition sch…
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C-band photons are recognized for having the lowest loss coefficient in optical fibers, making them highly favorable for optical fiber-based communication. In this study, we systematically investigated the temporal width of C-band heralded single photons and developed a theoretical model for biphoton generation via the spontaneous four-wave mixing (SFWM) process using a diamond-type transition scheme, which has not been previously reported. Our experimental data on temporal width closely aligns with the predictions of this model. Additionally, we introduced a new concept: the atomic velocity group relating to the two-photon resonance condition and the one-photon detuning in this atomic frame. These two parameters are crucial for understanding the behavior of the biphoton source. The concept indicates that the hot-atom source behaves similarly to the cold-atom source. Guided by our theoretical model, we observed 1529-nm (C-band) heralded single photons with a temporal width of 28.3$\pm$0.6 ns, corresponding to a linewidth of 11.0$\pm$0.2 MHz. For comparison, the ultimate linewidth limit is 6.1 MHz, determined by the natural linewidth of the atoms. Among all atom-based sources of 1300 to 1550 nm heralded single photons utilizing either cold or hot atoms, the temporal width achieved in this work represents the first instance of a width exceeding 10 ns, making it (or its linewidth) the longest (or narrowest) record to date. This work significantly enhances our understanding of diamond-type or cascade-type SFWM biphoton generation and marks an important milestone in achieving greater temporal width in atom-based sources of C-band heralded single photons.
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Submitted 5 July, 2025;
originally announced July 2025.
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Observation of Subnatural-Linewidth Biphotons In a Two-Level Atomic Ensemble
Authors:
Jyun-Kai Lin,
Tzu-Hsiang Chien,
Chin-Te Wu,
Ravikumar Chinnarasu,
Shengwang Du,
Ite A. Yu,
Chih-Sung Chuu
Abstract:
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 enab…
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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\times10^7$${\rm s}^{-1}{\rm mW}^{-1}{\rm MHz}^{-1}$, and a temporally symmetric wave packet at moderate optical depth. The strong non-classical cross-correlation of the biphotons also enables the observation of heralded sub-MHz-linewidth single photons with a pronounced single-photon nature. The generation of sub-MHz-linewidth biphotons and single photons with a two-level atomic ensembles not only finds applications in quantum repeaters and large cluster states for LDQC and LOQC but also opens up the opportunity to miniaturize the biphoton or single-photon sources for chip-scale quantum technologies.
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Submitted 21 January, 2025;
originally announced January 2025.
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Observation of Highly Correlated Ultrabright Biphotons Through Increased Atomic Ensemble Density in Spontaneous Four-Wave Mixing
Authors:
Jiun-Shiuan Shiu,
Zi-Yu Liu,
Chin-Yao Cheng,
Yu-Chiao Huang,
Ite A. Yu,
Ying-Cheng Chen,
Chih-Sung Chuu,
Che-Ming Li,
Shiang-Yu Wang,
Yong-Fan Chen
Abstract:
The pairing ratio, a crucial metric assessing a biphoton source's ability to generate correlated photon pairs, remains underexplored despite theoretical predictions. This study presents experimental findings on the pairing ratio, utilizing a double-$Λ$ spontaneous four-wave mixing biphoton source in cold atoms. At an optical depth (OD) of 20, we achieved an ultrahigh biphoton generation rate of up…
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The pairing ratio, a crucial metric assessing a biphoton source's ability to generate correlated photon pairs, remains underexplored despite theoretical predictions. This study presents experimental findings on the pairing ratio, utilizing a double-$Λ$ spontaneous four-wave mixing biphoton source in cold atoms. At an optical depth (OD) of 20, we achieved an ultrahigh biphoton generation rate of up to $1.3\times10^7$ per second, with a successful pairing ratio of $61\%$. Increasing the OD to 120 significantly improved the pairing ratio to $89\%$, while maintaining a consistent biphoton generation rate. This achievement, marked by high generation rates and robust biphoton pairing, holds great promise for advancing efficiency in quantum communication and information processing. Additionally, in a scenario with a lower biphoton generation rate of $5.0 \times 10^4$ per second, we attained an impressive signal-to-background ratio of 241 for the biphoton wavepacket, surpassing the Cauchy-Schwarz criterion by approximately $1.5\times10^4$ times.
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Submitted 10 February, 2024; v1 submitted 19 December, 2023;
originally announced December 2023.
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Experimental Demonstration of Stationary Dark-State Polaritons Dressed by Dipole-Dipole Interaction
Authors:
Bongjune Kim,
Ko-Tang Chen,
Kuei-You Chen,
Yu-Shan Chiu,
Chia-Yu Hsu,
Yi-Hsin Chen,
Ite A. Yu
Abstract:
Dark-state polaritons (DSPs) based on the effect of electromagnetically induced transparency are bosonic quasiparticles, representing the superpositions of photons and atomic ground-state coherences. It has been proposed that stationary DSPs are governed by the equation of motion closely similar to the Schrödinger equation and can be employed to achieve Bose-Einstein condensation (BEC) with transi…
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Dark-state polaritons (DSPs) based on the effect of electromagnetically induced transparency are bosonic quasiparticles, representing the superpositions of photons and atomic ground-state coherences. It has been proposed that stationary DSPs are governed by the equation of motion closely similar to the Schrödinger equation and can be employed to achieve Bose-Einstein condensation (BEC) with transition temperature orders of magnitude higher than that of the atomic BEC. The stationary-DSP BEC is a three-dimensional system and has a far longer lifetime than the exciton-polariton BEC. In this work, we experimentally demonstrated the stationary DSP dressed by the Rydberg-state dipole-dipole interaction (DDI). The DDI-induced phase shift of the stationary DSP was systematically studied. Notably, the experimental data are consistent with the theoretical predictions. The phase shift can be viewed as a consequence of elastic collisions. In terms of thermalization to achieve BEC, the $μ$m$^2$-size interaction cross-section of the DDI can produce a sufficient elastic collision rate for the stationary DSPs. This work makes a substantial advancement toward the realization of the stationary-DSP BEC.
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Submitted 31 August, 2023; v1 submitted 11 December, 2022;
originally announced December 2022.
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Temporally-ultralong biphotons with a linewidth of 50 kHz
Authors:
Yu-Sheng Wang,
Kai-Bo Li,
Chao-Feng Chang,
Tan-Wen Lin,
Jian-Qing Li,
Shih-Si Hsiao,
Jia-Mou Chen,
Yi-Hua Lai,
Ying-Cheng Chen,
Yong-Fan Chen,
Chih-Sung Chuu,
Ite A. Yu
Abstract:
We report the generation of biphotons, with a temporal full width at the half maximum (FWHM) of 13.4$\pm$0.3 $μ$s and a spectral FWHM of 50$\pm$1 kHz, via the process of spontaneous four-wave mixing. The temporal width is the longest, and the spectral linewidth is the narrowest up to date. This is also the first biphoton result that obtains a linewidth below 100 kHz, reaching a new milestone. The…
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We report the generation of biphotons, with a temporal full width at the half maximum (FWHM) of 13.4$\pm$0.3 $μ$s and a spectral FWHM of 50$\pm$1 kHz, via the process of spontaneous four-wave mixing. The temporal width is the longest, and the spectral linewidth is the narrowest up to date. This is also the first biphoton result that obtains a linewidth below 100 kHz, reaching a new milestone. The very long biphoton wave packet has a signal-to-background ratio of 3.4, which violates the Cauchy-Schwarz inequality for classical light by 4.8 folds. Furthermore, we demonstrated a highly-tunable-linewidth biphoton source and showed that while the biphoton source's temporal and spectral width were controllably varied by about 24 folds, its generation rate only changed by less than 15\%. A spectral brightness or generation rate per pump power per linewidth of 1.2$\times$10$^6$ pairs/(s$\cdot$mW$\cdot$MHz) was achieved at the temporal width of 13.4 $μ$s. The above results were made possible by the low decoherence rate and high optical depth of the experimental system, as well as the nearly phase-mismatch-free scheme employed in the experiment. This work has demonstrated a high-efficiency ultranarrow-linewidth biphoton source, and has made a substantial advancement in the quantum technology utilizing heralded single photons.
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Submitted 27 May, 2022;
originally announced May 2022.
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Increasing decoherence rate of Rydberg polaritons due to accumulating dark Rydberg atoms
Authors:
Ko-Tang Chen,
Bongjune Kim,
Chia-Chen Su,
Shih-Si Hsiao,
Shou-Jou Huang,
Wen-Te Liao,
Ite A. Yu
Abstract:
We experimentally observed an accumulative type of nonlinear attenuation and distortion of slow light, i.e., Rydberg polaritons, with the Rydberg state $|32D_{5/2}\rangle$ in the weak-interaction regime. The present effect of attenuation and distortion cannot be explained by considering only the dipole-dipole interaction (DDI) between Rydberg atoms in $|32D_{5/2}\rangle$. Our observation can be at…
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We experimentally observed an accumulative type of nonlinear attenuation and distortion of slow light, i.e., Rydberg polaritons, with the Rydberg state $|32D_{5/2}\rangle$ in the weak-interaction regime. The present effect of attenuation and distortion cannot be explained by considering only the dipole-dipole interaction (DDI) between Rydberg atoms in $|32D_{5/2}\rangle$. Our observation can be attributed to the atoms in the dark Rydberg states other than those in the bright Rydberg state, i.e., $|32D_{5/2}\rangle$, driven by the coupling field. The dark Rydberg states are all the possible states, in which the population decaying from $|32D_{5/2}\rangle$ accumulated over time, and they were not driven by the coupling field. Consequently, the DDI between the dark and bright Rydberg atoms increased the decoherence rate of the Rydberg polaritons. We performed three different experiments to verify the above hypothesis, to confirm the existence of the dark Rydberg states, and to measure the decay rate from the bright to dark Rydberg states. In the theoretical model, we included the decay process from the bright to dark Rydberg states and the DDI effect induced by both the bright and dark Rydberg atoms. All the experimental data of slow light taken at various probe Rabi frequencies were in good agreement with the theoretical predictions based on the model. This study pointed out an additional decoherence rate in the Rydberg-EIT effect, and provides a better understanding of the Rydberg-polariton system.
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Submitted 9 April, 2022; v1 submitted 13 October, 2021;
originally announced October 2021.
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Room-temperature biphoton source with a spectral brightness near the ultimate limit
Authors:
Jia-Mou Chen,
Chia-Yu Hsu,
Wei-Kai Huang,
Shih-Si Hsiao,
Fu-Chen Huang,
Yi-Hsin Chen,
Chih-Sung Chuu,
Ying-Cheng Chen,
Yong-Fan Chen,
Ite A. Yu
Abstract:
The biphotons, 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 br…
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The biphotons, 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 biphotons with a linewidth of 960 kHz and a generation rate of 3.7$\times$ $10^5$ pairs/s. The high generation rate, together with the narrow linewidth, results in a spectral brightness of 3.8$\times$ $10^5$ pairs/s/MHz, which is 17 times of the previous best result with atomic vapors and also better than all known results with all kinds of media. The all-copropagating scheme together with a large optical depth (OD) of the atomic vapor 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 3.6 folds. 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 enhanced by further increasing the OD. This work demonstrates a significant advancement and provides useful knowledge in the quantum technology using photons.
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Submitted 8 May, 2022; v1 submitted 19 September, 2021;
originally announced September 2021.
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Efficient Generation of Subnatural-Linewidth Biphotons by Controlled Quantum Interference
Authors:
Ravikumar Chinnarasu,
Chi-Yang Liu,
Yi-Feng Ding,
Chuan-Yi Lee,
Tsung-Hua Hsieh,
Ite A. Yu,
Chih-Sung Chuu
Abstract:
Biphotons of narrow bandwidth and long temporal length play a crucial role in long-distance quantum communication (LDQC) and linear optical quantum computing (LOQC). However, generation of these photons usually requires atomic ensembles with high optical depth or spontaneous parametric down-conversion with sophisticated optical cavity. By manipulating the two-component biphoton wavefunction genera…
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Biphotons of narrow bandwidth and long temporal length play a crucial role in long-distance quantum communication (LDQC) and linear optical quantum computing (LOQC). However, generation of these photons usually requires atomic ensembles with high optical depth or spontaneous parametric down-conversion with sophisticated optical cavity. By manipulating the two-component biphoton wavefunction generated from a low-optical-depth (low-OD) atomic ensemble, we demonstrate biphotons with subnatural linewidth in the sub-MHz regime. The potential of shaping and manipulating the quantum wavepackets of these temporally long photons is also demonstrated and discussed. Our work has potential applications in realizing quantum repeaters and large cluster states for LDQC and LOQC, respectively. The possibility to generate and manipulate subnatural-linewidth biphotons with low OD also opens up new opportunity to miniaturize the biphoton source for implementing quantum technologies on chip-scale quantum devices.
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Submitted 8 September, 2020;
originally announced September 2020.
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A Weakly-Interacting Many-Body System of Rydberg Polaritons Based on Electromagnetically Induced Transparency
Authors:
Bongjune Kim,
Ko-Tang Chen,
Shih-Si Hsiao,
Sheng-Yang Wang,
Kai-Bo Li,
Julius Ruseckas,
Gediminas Juzeliunas,
Teodora Kirova,
Marcis Auzinsh,
Ying-Cheng Chen,
Yong-Fan Chen,
Ite A. Yu
Abstract:
We proposed utilizing a medium with a high optical depth (OD) and a Rydberg state of low principal quantum number, $n$, to create a weakly-interacting many-body system of Rydberg polaritons, based on the effect of electromagnetically induced transparency (EIT). We experimentally verified the mean field approach to weakly-interacting Rydberg polaritons, and observed the phase shift and attenuation…
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We proposed utilizing a medium with a high optical depth (OD) and a Rydberg state of low principal quantum number, $n$, to create a weakly-interacting many-body system of Rydberg polaritons, based on the effect of electromagnetically induced transparency (EIT). We experimentally verified the mean field approach to weakly-interacting Rydberg polaritons, and observed the phase shift and attenuation induced by the dipole-dipole interaction (DDI). The DDI-induced phase shift or attenuation can be viewed as a consequence of the elastic or inelastic collisions among the Rydberg polaritons. Using a weakly-interacting system, we further observed that a larger DDI strength caused a width of the momentum distribution of Rydberg polaritons at the exit of the system to become notably smaller as compared with that at the entrance. In this study, we took $n =32$ and the atomic (or polariton) density of 5$\times10^{10}$ (or 2$\times10^{9}$) cm$^{-3}$. The observations demonstrate that the elastic collisions are sufficient to drive the thermalization process in this weakly-interacting many-body system. The combination of the $μ$s-long interaction time due to the high-OD EIT medium and the $μ$m$^2$-size collision cross section due to the DDI suggests a new and feasible platform for the Bose-Einstein condensation of the Rydberg polaritons.
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Submitted 24 May, 2021; v1 submitted 24 June, 2020;
originally announced June 2020.
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Mean field theory of weakly-interacting Rydberg polaritons in the EIT system based on the nearest-neighbor distribution
Authors:
Shih-Si Hsiao,
Ko-Tang Chen,
Ite A. Yu
Abstract:
The combination of high optical nonlinearity in the electromagnetically induced transparency (EIT) effect and strong electric dipole-dipole interaction (DDI) among the Rydberg-state atoms can lead to important applications in quantum information processing and many-body physics. One can utilize the Rydberg-EIT system in the strongly-interacting regime to mediate photon-photon interaction or qubit-…
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The combination of high optical nonlinearity in the electromagnetically induced transparency (EIT) effect and strong electric dipole-dipole interaction (DDI) among the Rydberg-state atoms can lead to important applications in quantum information processing and many-body physics. One can utilize the Rydberg-EIT system in the strongly-interacting regime to mediate photon-photon interaction or qubit-qubit operation. One can also employ the Rydberg-EIT system in the weaklyinteracting regime to study the Bose-Einstein condensation of Rydberg polaritons. Most of the present theoretical models dealt with the strongly-interacting cases. Here, we consider the weaklyinteracting regime and develop a mean field model based on the nearest-neighbor distribution. Using the mean field model, we further derive the analytical formulas for the attenuation coefficient and phase shift of the output probe field. The predictions from the formulas are consistent with the experimental data in the weakly-interacting regime, verifying the validity of our model. As the DDI-induced phase shift and attenuation can be seen as the consequences of elastic and inelastic collisions among particles, this work provides a very useful tool for conceiving ideas relevant to the EIT system of weakly-interacting Rydberg polaritons, and for evaluating experimental feasibility.
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Submitted 11 September, 2020; v1 submitted 16 June, 2020;
originally announced June 2020.
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Low-Loss High-Fidelity Frequency-Mode Hadamard Gates Based on Electromagnetically Induced Transparency
Authors:
Kao-Fang Chang,
Ta-Pang Wang,
Chun-Yi Chen,
Yi-Hsin Chen,
Yu-Sheng Wang,
Yong-Fan Chen,
Ying-Cheng Chen,
Ite A. Yu
Abstract:
A frequency beam splitter (FBS) with the split ratio of 0.5 or 1 can be used as the frequency-mode Hadamard gate (FHG) for frequency-encoded photonic qubits or as the quantum frequency converter (QFC) for frequency up or down conversion of photons. Previous works revealed that all kinds of the FHG or QFC operating at the single-photon level had overall efficiency or output-to-input ratio around 50…
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A frequency beam splitter (FBS) with the split ratio of 0.5 or 1 can be used as the frequency-mode Hadamard gate (FHG) for frequency-encoded photonic qubits or as the quantum frequency converter (QFC) for frequency up or down conversion of photons. Previous works revealed that all kinds of the FHG or QFC operating at the single-photon level had overall efficiency or output-to-input ratio around 50% or less. In this work, our FHG and QFC are made with the four-wave mixing process based on the dual-$Λ$ electromagnetically induced transparency scheme. We achieved an overall efficiency of 90$\pm$4% in the FGH and that of 84% in the QFC using coherent-state single photons, both of which are the best up-to-date records. To test the fidelity of the FBS, we propose a novel scheme of Hong-Ou-Mandel interference (HOMI) for quantum process tomography. The fidelity indicated by the HOMI's $g^{(2)}$ measurement of the FHG is 0.99$\pm$0.01. Such low-loss high-fidelity FHG and QFC or FBS with the tunable split ratio can lead to useful operations or devices in long-distance quantum communication.
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Submitted 14 August, 2019; v1 submitted 7 July, 2019;
originally announced July 2019.
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Effect of laser frequency fluctuation on the decay rate of Rydberg coherence
Authors:
Bongjune Kim,
Ko-Tang Chen,
Chia-Yu Hsu,
Shih-Si Hsiao,
Yu-Chih Tseng,
Chin-Yuan Lee,
Shih-Lun Liang,
Yi-Hua Lai,
Julius Ruseckas,
Gediminas Juzeliunas,
Ite A. Yu
Abstract:
The effect of electromagnetically induced transparency (EIT) combined with Rydberg-state atoms provides high optical nonlinearity to efficiently mediate the photon-photon interaction. However, the decay rate of Rydberg coherence, i.e., the decoherence rate, plays an important role in optical nonlinear efficiency, and can be largely influenced by laser frequency fluctuation. In this work, we carrie…
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The effect of electromagnetically induced transparency (EIT) combined with Rydberg-state atoms provides high optical nonlinearity to efficiently mediate the photon-photon interaction. However, the decay rate of Rydberg coherence, i.e., the decoherence rate, plays an important role in optical nonlinear efficiency, and can be largely influenced by laser frequency fluctuation. In this work, we carried out a systematic study of the effect of laser frequency fluctuation on the decoherence rate. We derived an analytical formula that quantitatively describes the relationship between the decoherence rate and laser frequency fluctuation. The formula was experimentally verified by using the $Λ$-type EIT system of laser-cooled $^{87}$Rb atoms, in which one can either completely eliminate or controllably introduce the effect of laser frequency fluctuation. We also included the effect of Doppler shift caused by the atomic thermal motion in the formula, which can be negligible in the $Λ$-type EIT experiment but significant in the Rydberg-EIT experiment. Utilizing the atoms of 350 $μ$K, we studied the decoherence rate in the Rydberg-EIT system involving with the state of $|32D_{5/2}\rangle$. The experimental data are consistent with the predictions from the formula. We were able to achieve a rather low decoherence rate of $2π\times$48 kHz at a moderate coupling Rabi frequency of $2π\times$4.3 MHz.
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Submitted 13 June, 2019; v1 submitted 26 February, 2019;
originally announced February 2019.
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Enhanced spectral profile in the study of Doppler-broadened Rydberg atoms
Authors:
Bo-Han Wu,
Ya-Wen Chuang,
Yi-Hsin Chen,
Jr-Chiun Yu,
Ming-Shien Chang,
Ite A. Yu
Abstract:
Combination of the electromagnetically-induced-transparency (EIT) effect and Rydberg-state atoms has attracted great attention recently due to its potential application in the photon-photon interaction or qubit operation. In this work, we studied the Rydberg-EIT spectra with room-temperature $^{87}$Rb atoms. Spectroscopic data under various experimental parameters all showed that the contrast of E…
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Combination of the electromagnetically-induced-transparency (EIT) effect and Rydberg-state atoms has attracted great attention recently due to its potential application in the photon-photon interaction or qubit operation. In this work, we studied the Rydberg-EIT spectra with room-temperature $^{87}$Rb atoms. Spectroscopic data under various experimental parameters all showed that the contrast of EIT transparency as a function of the probe intensity is initially enhanced, reaches a maximum value and then decays gradually. The contrast of spectral profile at the optimum probe field intensity is enhanced by $2-4$ times as compared with that at weak intensity. Moreover, the signal-to-noise ratio of the spectrum can potentially be improved by 1 or 2 order of magnitude. We provided a theoretical model to explain this behavior and clarified its underlying mechanism. Our work overcomes the obstacle of weak signal in the Rydberg-EIT spectrum caused by an apparent relaxation rate of the Rydberg polariton and weak coupling transition strength, and provides the useful knowledge for the Rydberg-EIT study.
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Submitted 11 April, 2017;
originally announced April 2017.
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Setting a disordered password on a photonic memory
Authors:
Shih-Wei Su,
Shih-Chuan Gou,
Lock Yue Chew,
Yu-Yen Chang,
Ite A. Yu,
Alexey Kalachev,
Wen-Te Liao
Abstract:
Encryption is a vital tool of information technology protecting our data in the world with ubiquitous computers. While photons are regarded as ideal information carriers, it is a must to implement such data protection on all-optical storage. However, the intrinsic risk of data breaches in existing schemes of photonic memory was never addressed. We theoretically demonstrate the first protocol using…
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Encryption is a vital tool of information technology protecting our data in the world with ubiquitous computers. While photons are regarded as ideal information carriers, it is a must to implement such data protection on all-optical storage. However, the intrinsic risk of data breaches in existing schemes of photonic memory was never addressed. We theoretically demonstrate the first protocol using spatially disordered laser fields to encrypt data stored on an optical memory, namely, encrypted photonic memory. Compare with a digital key, a continuous disorder encrypts stored light pulses with a rather long key length against brute-force attacks. To address the broadband storage, we also investigate a novel scheme of disordered echo memory with a high fidelity approaching unity. Our results pave novel ways to encrypt different schemes of photonic memory based on quantum optics and raise the security level of photonic information technology.
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Submitted 1 November, 2016;
originally announced November 2016.
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Phase-dependent double-Λ electromagnetically induced transparency
Authors:
Yi-Hsin Chen,
Pin-Ju Tsai,
Ite A. Yu,
Ying-Cheng Chen,
Yong-Fan Chen
Abstract:
We theoretically investigate a double-Λ electromagnetically induced transparency (EIT) system. The property of the double-Λ medium with a closed-loop configuration depends on the relative phase of the applied laser fields. This phase-dependent mechanism differentiates the double-Λ medium from the conventional Kerr-based nonlinear medium, e.g., EIT-based nonlinear medium discussed by Harris and Hau…
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We theoretically investigate a double-Λ electromagnetically induced transparency (EIT) system. The property of the double-Λ medium with a closed-loop configuration depends on the relative phase of the applied laser fields. This phase-dependent mechanism differentiates the double-Λ medium from the conventional Kerr-based nonlinear medium, e.g., EIT-based nonlinear medium discussed by Harris and Hau [Phys. Rev. Lett. 82, 4611 (1999)], which depends only on the intensities of the applied laser fields. Steady-state analytical solutions for the phase-dependent system are obtained by solving the Maxwell-Bloch equations. In addition, we discuss efficient all-optical phase modulation and coherent light amplification based on the proposed double-Λ EIT scheme.
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Submitted 15 September, 2014;
originally announced September 2014.
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Experimental demonstration of spinor slow light
Authors:
Meng-Jung Lee,
Julius Ruseckas,
Chin-Yuan Lee,
Viaceslav Kudriasov,
Kao-Fang Chang,
Hung-Wen Cho,
Gediminas Juzeliunas,
Ite A. Yu
Abstract:
Slow light based on the effect of electromagnetically induced transparency is of great interest due to its applications in low-light-level nonlinear optics and quantum information manipulation. The previous experiments all dealt with the single-component slow light. Here we report the experimental demonstration of two-component or spinor slow light using a double tripod atom-light coupling scheme.…
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Slow light based on the effect of electromagnetically induced transparency is of great interest due to its applications in low-light-level nonlinear optics and quantum information manipulation. The previous experiments all dealt with the single-component slow light. Here we report the experimental demonstration of two-component or spinor slow light using a double tripod atom-light coupling scheme. The scheme involves three atomic ground states coupled to two excited states by six light fields. The oscillation due to the interaction between the two components was observed. Based on the stored light, our data showed that the double tripod scheme behaves like the two outcomes of an interferometer enabling precision measurements of frequency detuning. We experimentally demonstrated a possible application of the double tripod scheme as quantum memory/rotator for the two-color qubit. Our study also suggests that the spinor slow light is a better method than a widely-used scheme in the nonlinear frequency conversion.
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Submitted 26 November, 2014; v1 submitted 26 April, 2014;
originally announced April 2014.
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Radiation trapping inside a hollow-core photonic crystal fiber
Authors:
H. H. Jen,
Chang-Yi Wang,
Kevin C. J. Lee,
Yi-Hsin Chen,
Ite A. Yu
Abstract:
We report the radiation trapping effect inside a hollow-core photonic crystal fiber (PCF). An optical dipole trap was used to load and confine the atoms in the PCF without contacting the wall of the fiber. The transmission of a probe light propagating through the PCF was studied experimentally and theoretically. With the experimental results and theoretical predictions, we conclude that the radiat…
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We report the radiation trapping effect inside a hollow-core photonic crystal fiber (PCF). An optical dipole trap was used to load and confine the atoms in the PCF without contacting the wall of the fiber. The transmission of a probe light propagating through the PCF was studied experimentally and theoretically. With the experimental results and theoretical predictions, we conclude that the radiation trapping can play a significant role and should be taken into account in the spectroscopic measurements inside the PCF.
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Submitted 10 June, 2014; v1 submitted 23 April, 2014;
originally announced April 2014.
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Low-light-level four-wave mixing by quantum interference
Authors:
Chang-Kai Chiu,
Yi-Hsin Chen,
Yen-Chun Chen,
Ite A. Yu,
Ying-Cheng Chen,
Yong-Fan Chen
Abstract:
We observed electromagnetically-induced-transparency-based four-wave mixing (FWM) in the pulsed regime at low light levels. The FWM conversion efficiency of 3.8(9)% was observed in a four-level system of cold 87Rb atoms using a driving laser pulse with a peak intensity of approximately 80 μW/cm^2, corresponding to an energy of approximately 60 photons per atomic cross section. Comparison between t…
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We observed electromagnetically-induced-transparency-based four-wave mixing (FWM) in the pulsed regime at low light levels. The FWM conversion efficiency of 3.8(9)% was observed in a four-level system of cold 87Rb atoms using a driving laser pulse with a peak intensity of approximately 80 μW/cm^2, corresponding to an energy of approximately 60 photons per atomic cross section. Comparison between the experimental data and the theoretical predictions proposed by Harris and Hau [Phys. Rev. Lett. 82, 4611 (1999)] showed good agreement. Additionally, a high conversion efficiency of 46(2)% was demonstrated when applying this scheme using a driving laser intensity of approximately 1.8 mW/cm^2. According to our theoretical predictions, this FWM scheme can achieve a conversion efficiency of nearly 100% when using a dense medium with an optical depth of 500.
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Submitted 7 February, 2014; v1 submitted 20 November, 2013;
originally announced November 2013.
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Transfer of orbital angular momentum of light using two component slow light
Authors:
J. Ruseckas,
V. Kudriasov,
I. A. Yu,
G. Juzeliunas
Abstract:
We study the manipulation of slow light with an orbital angular momentum propagating in a cloud of cold atoms. Atoms are affected by four copropagating control laser beams in a double tripod configuration of the atomic energy levels involved, allowing to minimize the losses at the vortex core of the control beams. In such a situation the atomic medium is transparent for a pair of copropagating pro…
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We study the manipulation of slow light with an orbital angular momentum propagating in a cloud of cold atoms. Atoms are affected by four copropagating control laser beams in a double tripod configuration of the atomic energy levels involved, allowing to minimize the losses at the vortex core of the control beams. In such a situation the atomic medium is transparent for a pair of copropagating probe fields, leading to the creation of two-component (spinor) slow light. We study the interaction between the probe fields when two control beams carry optical vortices of opposite helicity. As a result, a transfer of the optical vortex takes place from the control to the probe fields without switching off and on the control beams. This feature is missing in a single tripod scheme where the optical vortex can be transferred from the control to the probe field only during either the storage or retrieval of light.
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Submitted 7 June, 2013;
originally announced June 2013.
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Few-Photon All-Optical π Phase modulation Based on a Double-Λ System
Authors:
Yen-Chun Chen,
Hao-Chung Chen,
Hsiang-Yu Lo,
Bing-Ru Tsai,
Ite A. Yu,
Ying-Cheng Chen,
Yong-Fan Chen
Abstract:
We propose an efficient all-optical phase modulation based on a double-Λ system and demonstrate a π phase shift of a few-photon pulse induced by another few-photon pulse in cold rubidium atoms with this scheme. By changing the phases of the applied laser fields, one can control the property of the double-Λ medium. This phase-dependent mechanism makes the double-Λ system different form the conventi…
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We propose an efficient all-optical phase modulation based on a double-Λ system and demonstrate a π phase shift of a few-photon pulse induced by another few-photon pulse in cold rubidium atoms with this scheme. By changing the phases of the applied laser fields, one can control the property of the double-Λ medium. This phase-dependent mechanism makes the double-Λ system different form the conventional cross-Kerr-based system which only depends on the applied laser intensities. The proposed scheme provides a new route to generate strong nonlinear interactions between photons, and may have potential for applications in quantum information technologies.
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Submitted 8 February, 2013; v1 submitted 7 February, 2013;
originally announced February 2013.
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Coherent Optical Memory with High Storage Efficiency and Large Fractional Delay
Authors:
Yi-Hsin Chen,
Meng-Jung Lee,
I-Chung Wang,
Shengwang Du,
Yong-Fan Chen,
Ying-Cheng Chen,
Ite A. Yu
Abstract:
A high-storage efficiency and long-lived quantum memory for photons is an essential component in long-distance quantum communication and optical quantum computation. Here, we report a 78% storage efficiency of light pulses in a cold atomic medium based on the effect of electromagnetically induced transparency (EIT). At 50% storage efficiency, we obtain a fractional delay of 74, which is the best u…
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A high-storage efficiency and long-lived quantum memory for photons is an essential component in long-distance quantum communication and optical quantum computation. Here, we report a 78% storage efficiency of light pulses in a cold atomic medium based on the effect of electromagnetically induced transparency (EIT). At 50% storage efficiency, we obtain a fractional delay of 74, which is the best up-to-date record. The classical fidelity of the recalled pulse is better than 90% and nearly independent of the storage time, as confirmed by the direct measurement of phase evolution of the output light pulse with a beat-note interferometer. Such excellent phase coherence between the stored and recalled light pulses suggests that the current result can be readily applied to single photon wave packets. Our work significantly advances the technology of EIT-based optical memory and may find practical applications in long-distance quantum communication and optical quantum computation.
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Submitted 21 February, 2013; v1 submitted 3 November, 2012;
originally announced November 2012.
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Electromagnetic induced transparency and slow light in interacting quantum degenerate atomic gases
Authors:
H. H. Jen,
Bo Xiong,
Ite A. Yu,
Daw-Wei Wang
Abstract:
We systematically develop the full quantum theory for the electromagnetic induced transparency (EIT) and slow light properties in ultracold Bose and Fermi gases. It shows a very different property from the classical theory which assumes frozen atomic motion. For example, the speed of light inside the atomic gases can be changed dramatically near the Bose-Einstein condensation temperature, while th…
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We systematically develop the full quantum theory for the electromagnetic induced transparency (EIT) and slow light properties in ultracold Bose and Fermi gases. It shows a very different property from the classical theory which assumes frozen atomic motion. For example, the speed of light inside the atomic gases can be changed dramatically near the Bose-Einstein condensation temperature, while the presence of the Fermi sea can destroy the EIT effect even at zero temperature. From experimental point of view, such quantum EIT property is mostly manifested in the counter-propagating excitation schemes in either the low-lying Rydberg transition with a narrow line width or in the D2 transitions with a very weak coupling field. We further investigate the interaction effects on the EIT for a weakly interacting Bose-Einstein condensate, showing an inhomogeneous broadening of the EIT profile and nontrivial change of the light speed due to the quantum many-body effects beyond mean field energy shifts.
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Submitted 13 December, 2012; v1 submitted 1 August, 2012;
originally announced August 2012.
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Demonstration of the Interaction between Two Stopped Light Pulses
Authors:
Yi-Hsin Chen,
Meng-Jung Lee,
Weilun Hung,
Ying-Cheng Chen,
Yong-Fan Chen,
Ite A. Yu
Abstract:
We report the first experimental demonstration that two light pulses were made motionless and interacted with each other via a medium. The interaction time is, in principle, as long as possible and a considerable efficiency can be achieved even below single-photon level. We utilized the optical process of one photon pulse switched by another based on the effect of electromagnetically induced trans…
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We report the first experimental demonstration that two light pulses were made motionless and interacted with each other via a medium. The interaction time is, in principle, as long as possible and a considerable efficiency can be achieved even below single-photon level. We utilized the optical process of one photon pulse switched by another based on the effect of electromagnetically induced transparency to demonstrate the enhancement of optical nonlinear efficiency. With moving light pulses, the switching is activated at energy per area of 2 photons per atomic absorption cross section in the best situation as discussed in [Phys. Rev. Lett. 82, 4611 (1999)]. With motionless light pulses, we demonstrated that the switching is activated at 0.56 photons per atomic absorption cross section and that the light level can be further reduced by increasing the optical density of the medium. Our work enters a new regime of low light physics.
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Submitted 9 November, 2011;
originally announced November 2011.
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An effective thermal-parametrization theory for the slow-light dynamics in a Doppler-broadened electomagnetically induced transparency medium
Authors:
Shih-Wei Su,
Yi-Hsin Chen,
Shih-Chuan Gou,
Ite A. Yu
Abstract:
We model the effects of atomic thermal motion on the propagation of a light pulse in an electromagnetically induced transparency medium by introducing a set of effectively temperature-dependent parameters, including the Rabi frequency of the coupling field, optical density and relaxation rate of the ground state coherence, into the governing equations. The validity of this effective theory is veri…
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We model the effects of atomic thermal motion on the propagation of a light pulse in an electromagnetically induced transparency medium by introducing a set of effectively temperature-dependent parameters, including the Rabi frequency of the coupling field, optical density and relaxation rate of the ground state coherence, into the governing equations. The validity of this effective theory is verified by the close agreement between the theoretical results and the experimental data.
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Submitted 31 May, 2011;
originally announced May 2011.
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Dynamics of slow light and light storage in a Doppler-broadened electromagnetically-induced-transparency medium: A numerical approach
Authors:
Shih-Wei Su,
Yi-Hsin Chen,
Shih-Chuan Gou,
Tzyy-Leng Horng,
Ite A. Yu
Abstract:
We present a numerical scheme to study the dynamics of slow light and light storage in an electromagneticallyinduced- transparency (EIT) medium at finite temperatures. Allowing for the motional coupling, we derive a set of coupled Schrödinger equations describing a boosted closed three-level EIT system according to the principle of Galilean relativity. The dynamics of a uniformly moving EIT medium…
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We present a numerical scheme to study the dynamics of slow light and light storage in an electromagneticallyinduced- transparency (EIT) medium at finite temperatures. Allowing for the motional coupling, we derive a set of coupled Schrödinger equations describing a boosted closed three-level EIT system according to the principle of Galilean relativity. The dynamics of a uniformly moving EIT medium can thus be determined by numerically integrating the coupled Schrödinger equations for atoms plus one ancillary Maxwell-Schrödinger equation for the probe pulse. The central idea of this work rests on the assumption that the loss of ground-state coherence at finite temperatures can be ascribed to the incoherent superposition of density matrices representing the EIT systems with various velocities. Close agreements are demonstrated in comparing the numerical results with the experimental data for both slow light and light storage. In particular, the distinct characters featuring the decay of ground-state coherence can be well verified for slow light and light storage. This warrants that the current scheme can be applied to determine the decaying profile of the ground-state coherence as well as the temperature of the EIT medium.
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Submitted 31 May, 2011;
originally announced May 2011.
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Hiding Single Photons With Spread Spectrum Technology
Authors:
Chinmay Belthangady,
Chih-Sung Chuu,
Ite A. Yu,
G. Y. Yin,
J. M. Kahn,
S. E. Harris
Abstract:
We describe a proof-of-principal experiment demonstrating the use of spread spectrum technology at the single photon level. We show how single photons with a prescribed temporal shape, in the presence of interfering noise, may be hidden and recovered.
We describe a proof-of-principal experiment demonstrating the use of spread spectrum technology at the single photon level. We show how single photons with a prescribed temporal shape, in the presence of interfering noise, may be hidden and recovered.
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Submitted 1 April, 2010;
originally announced April 2010.
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Stationary Light Pulses in Cold Atomic Media
Authors:
Wen-Te Liao,
Yen-Wei Lin,
Thorsten Peters,
Hung-Chih Chou,
Jian-Siung Wang,
Pei-Chen Kuan,
Ite A. Yu
Abstract:
Stationary light pulses (SLPs), i.e., light pulses without motion, are formed via the retrieval of stored probe pulses with two counter-propagating coupling fields. We show that there exist non-negligible hybrid Raman excitations in media of cold atoms that prohibit the SLP formation. We experimentally demonstrate a method to suppress these Raman excitations and realize SLPs in laser-cooled atom…
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Stationary light pulses (SLPs), i.e., light pulses without motion, are formed via the retrieval of stored probe pulses with two counter-propagating coupling fields. We show that there exist non-negligible hybrid Raman excitations in media of cold atoms that prohibit the SLP formation. We experimentally demonstrate a method to suppress these Raman excitations and realize SLPs in laser-cooled atoms. Our work opens the way to SLP studies in cold as well as in stationary atoms and provides a new avenue to low-light-level nonlinear optics.
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Submitted 17 November, 2008;
originally announced November 2008.
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Stationary Light Pulses without Bragg Gratings
Authors:
Yen-Wei Lin,
Hung-Chih Chou,
Thorsten Peters,
Wen-Te Liao,
Hung-Wen Cho,
Pei-Chen Guan,
Ite A. Yu
Abstract:
The underlying mechanism of the stationary light pulse (SLP) was identified as a band gap being created by a Bragg grating formed by two counter-propagating coupling fields of similar wavelength. Here we present a more general view of the formation of SLPs, namely several balanced four-wave mixing processes sharing the same ground-state coherence. Utilizing this new concept we report the first e…
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The underlying mechanism of the stationary light pulse (SLP) was identified as a band gap being created by a Bragg grating formed by two counter-propagating coupling fields of similar wavelength. Here we present a more general view of the formation of SLPs, namely several balanced four-wave mixing processes sharing the same ground-state coherence. Utilizing this new concept we report the first experimental observation of a bichromatic SLP at wavelengths for which no Bragg grating can be established. We also demonstrate the production of a SLP directly from a propagating light pulse without prior storage. Being easily controlled externally makes SLPs a very versatile tool for low-light-level nonlinear optics and quantum information manipulation.
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Submitted 6 October, 2008;
originally announced October 2008.
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Observation of Single-Photon Switching
Authors:
Yong-Fan Chen,
Zen-Hsiang Tsai,
Yu-Chen Liu,
Ite A. Yu
Abstract:
We report an experimental demonstration of single-photon switching in laser-cooled $^{87}$Rb atoms. A resonant probe pulse with an energy per unit area of one photon per $λ^2/2π$ propagates through the optically thick atoms. Its energy transmittance is greater than 63% or loss is less than $e^{-1}$ due to the effect of electromagnetically induced transparency. In the presence of a switching puls…
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We report an experimental demonstration of single-photon switching in laser-cooled $^{87}$Rb atoms. A resonant probe pulse with an energy per unit area of one photon per $λ^2/2π$ propagates through the optically thick atoms. Its energy transmittance is greater than 63% or loss is less than $e^{-1}$ due to the effect of electromagnetically induced transparency. In the presence of a switching pulse with an energy per unit area of 1.4 photons per $λ^2/2π$, the energy transmittance of the same probe pulse becomes less than 37% or $e^{-1}$. This substantial reduction of the probe transmittance caused by single switching photons has potential applications in single-photon-level nonlinear optics and the manipulation of quantum information.
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Submitted 31 January, 2005;
originally announced January 2005.