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Characterizing micro-macro transitions with slow light

Zhifan Zhou, Ulrich Vogl, Ryan T. Glasser, Zhongzhong Qin, Yami Fang, Jietai Jing, Weiping Zhang

Published May 24, 2016• 0 citations
OpenAlex

Abstract

The transition between the microscopic to the macroscopic world is of broad fundamental and technological significance. Optical parametric amplifiers allow for amplifying single photons to the macroscopic level, but the underlying temporal dynamics are still not well understood. Slow light, in which the group velocity is delayed via quantum interference, is an effective tool to interrogate the temporal dynamics of light-matter interactions. Here, we demonstrate a scheme to characterize micro-macro transitions with slow light based on a four-wave mixing linear amplification process in a hot rubidium vapour. The scheme exhibits strong dispersion which is sensitive to the input's change at the single-photon level, resulting in a nonlinear decay of the micro-macro transition time with the increased microscopic input. The present system is suitable for the study of the relevant time scale of quantum-to-classical transitions and the potential impact from fundamental effects such as gravity, as indicated by recent proposals.

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Fundamentally, the dynamics of micro-macro transitions is instrumental to understanding the process of quantum-to-classical transitions; technologically, it can also facilitate the detection of the microscopic signals in quantum experiments via convenient detectors. Here, we demonstrate a scheme to characterize micro-macro transitions based on a four-wave mixing linear optical amplification process in a hot rubidium vapor. The linear optical amplifier provides a large optical gain of $10^7$ for injected single-photon-level pulses, enabling photon-number-resolving detection by average via non-single-photon counting detectors with a large dynamic range. The scheme exhibits strong dispersion which is sensitive to the input's change at the single-photon level, resulting in the group-velocity delay time scaling with $1/\sqrt{N}$, where $N$ is the average input photon number. The output probe and conjugate modes have different coefficients of this $1/\sqrt{N}$ scaling, indicating the coefficient can serve as an efficient parameter to characterize the specified micro-macro transitions. The demonstrated results are generally applicable for quantum detection and optical signal processing in light-atom interfaces. Furthermore, the present system is suitable for the study of relevant time-resolved dynamics of the quantum-to-classical transitions.

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Research into slow light began theoretically in 1880 with the paper [1] of H A Lorentz, who is best known for his work on relativity and the speed of light. Experimental work started some 60 years later with the work of S L McCall and E L Hahn [2] who explored non-linear self-induced transparency in ruby. This field of research has burgeoned in the last 10 years, starting with the work of L Vestergaard Hau and coworkers on slow light via electromagnetically induced transparency in a Bose–Einstein condensate [3]. Many groups are now able to slow light down to a few metres per second or even stop the motion of light entirely [4]. Today, slow light – or more often `slow and fast light' – has become its own vibrant field with a strongly increasing number of publications. In broad scope, slow light research can be categorized in terms of the sort of physical mechanism used to slow down the light. One sort of slow light makes use of material dispersion. This dispersion can be the natural dispersion of the ordinary refractive index or can be the frequency dependence of some nonlinear optical process, such as electromagnetically induced transparency, coherent population oscillations, stimulated light scattering, or four-wave mixing processes. The second sort of slow light makes use of the wavelength dependence of artificially structured materials, such as photonic crystals, optical waveguides, and collections of microresonators. Material systems in which slow light has been observed include metal vapours, rare-earth-doped materials, Raman and Brillioun gain media, photonic crystals, microresonators and, more recently, metamaterials. A common feature of all of these schemes is the presence of a sharp single resonance or multiple resonances produced by an atomic transition, a resonance in a photonic structure, or in a nonlinear optical process. Current applications of slow light include a series of attractive topics in optical information processing, such as optical data storage, optical memories, quantum information devices, and optical communication systems in which the use of slow light will allow all-optical processing with less wasted heat. To implement these applications, devices such as buffers, memories, interferometers and switches that utilize slow light need to be developed. Future challenges include the need for improved coupling of light into slow light modes, overcoming propagation losses, and mitigating the influence of large dispersion of the group velocity. The collection of papers in this special issue of Journal of Optics features a broad spectrum of articles that highlight actual developments in many of the material types and schemes described above. It represents therefore an excellent up to date snapshot of the current state of the field of slow light research. References [1] Lorentz H A 1880 Uber die Beziehung zwischen der Fortpflanzung des Lichtes und der Körperdichte Wiedemann Ann. 9 641–64 [2] McCall S L and Hahn E L 1967 Self-induced transparency by pulsed coherent light Phys. Rev. Lett. 18 908–11 [3] Vestergaard Hau L, Harris S E, Dutton Z and Behroozi C H 1999 Nature 397 594 [4] Philips D F, Fleischhauer A, Mair A, Walsworth R L and Lukin M D 2001 Storage of light in atomic vapor Phys. Rev. Lett. 86 783–6

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Electromagnetic pulse propagation in the slow light regime and near a zero group velocity point is relevant to a plethora of potential applications, and has analogies in numerous other wave systems. Unfortunately, the standard frequency-based formulation for pulse propagation is unsuitable for describing the dynamics in such regimes, due to the divergence of the dispersion coefficients. Moreover, in the presence of absorption, it is not clear how to interpret the propagation dynamics due to the drastic change induced by absorption upon the dispersion curves. As a remedy, we present an alternative momentum-based formulation, which is rapidly converging in these regimes, and naturally suitable for lossy and nonlinear media. It is specialized to a waveguide geometry which provides a significant simplification with respect to existing momentum-based schemes. Doing so, we provide a somewhat alternative, yet intuitive picture of the seeming enhanced absorption and nonlinear response in these regimes, and show that light-matter interactions are not enhanced in the slow/stopped light regimes.

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Summary form only given. Slow light has been explored for building quantum networks, with particular interest in slowing the group velocity of single photons [1], and more recently exploited to enhance the measurement of small phase shifts. Generally, slow-light effects have been characterized as the net effect of a pulse propagating through the slow-light medium, i.e., as a pulse delay time Δt measured with a fast photodiode at the output of the medium [2]. In this work, we use a single-photon imaging camera to observe slow light in situ, and thus provide a direct measurement of spatial pulse compression and temporal dispersion as the pulse travels through the slow light medium, in this case a hyperfine absorption doublet in hot Rb vapor. Our method combines light-in-flight imaging techniques with a camera comprised of an array of single-photon avalanche diodes (SPAD camera) [3] to image the photons scattered by the Rb vapor in the direction of the camera as shown in Fig. 1(a). In addition, the single photon nature of the SPAD detector allows us to obtain a measurement of the single photon group velocity. As shown in Fig. 1(c) and (d), we observe a significant delay, on the order of nanoseconds, in the detection of the photons scattered when the pulse first enters the slow-light medium. This lag in scattered-photon arrival time is a direct visualization of the slowing down of the single-photon group velocity. The pulses used here had a temporal full width at half maximum (FWHM) of τ ~1 ns, with measured group velocities as low as vg~ 0.006c. At these low group velocities we observe a full fractional pulse delay of up to F D = Δt/τ ~ 40 over 7 cm of propagation, and F D ~ 5 for the scattered single photons, which propagate through ~ 1 cm of Rb vapor prior to exiting the cell en-route to the camera.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2017•0 citations

Everything is slow light (Conference Presentation)

Jacob B. Khurgin

In this talk I explain that enhancement of performance of almost any optical device such as sensor modulator, amplifier or any nonlinear device in the end intimately connected to increasing the time of light-matter interaction, i.e. reducing the group velocity of light. Such similarly different phenomena as ENZ (epsilon near zero), plasmonics, micro-cavities and photonic crystals can all be characterized using the same slow light formalism.

•Mar 5, 2019•0 citations
The transition between the microscopic to the macroscopic world is of broad fundamental and technological significance. Optical parametric amplifiers allow for amplifying single photons to the macroscopic level, but the underlying temporal dynamics are still not well understood. Slow light, in which the group velocity is delayed via quantum interference, is an effective tool to interrogate the temporal dynamics of light-matter interactions. Here, we demonstrate a scheme to characterize micro-macro transitions with slow light based on a four-wave mixing linear amplification process in a hot rubidium vapour. The scheme exhibits strong dispersion which is sensitive to the input's change at the single-photon level, resulting in a nonlinear decay of the micro-macro transition time with the increased microscopic input. The present system is suitable for the study of the relevant time scale of quantum-to-classical transitions and the potential impact from fundamental effects such as gravity, as indicated by recent proposals.
Fundamentally, the dynamics of micro-macro transitions is instrumental to understanding the process of quantum-to-classical transitions; technologically, it can also facilitate the detection of the microscopic signals in quantum experiments via convenient detectors. Here, we demonstrate a scheme to characterize micro-macro transitions based on a four-wave mixing linear optical amplification process in a hot rubidium vapor. The linear optical amplifier provides a large optical gain of 10710^7107 for injected single-photon-level pulses, enabling photon-number-resolving detection by average via non-single-photon counting detectors with a large dynamic range. The scheme exhibits strong dispersion which is sensitive to the input's change at the single-photon level, resulting in the group-velocity delay time scaling with 1/N1/\sqrt{N}1/N​, where NNN is the average input photon number. The output probe and conjugate modes have different coefficients of this 1/N1/\sqrt{N}1/N​ scaling, indicating the coefficient can serve as an efficient parameter to characterize the specified micro-macro transitions. The demonstrated results are generally applicable for quantum detection and optical signal processing in light-atom interfaces. Furthermore, the present system is suitable for the study of relevant time-resolved dynamics of the quantum-to-classical transitions.
Research into slow light began theoretically in 1880 with the paper [1] of H A Lorentz, who is best known for his work on relativity and the speed of light. Experimental work started some 60 years later with the work of S L McCall and E L Hahn [2] who explored non-linear self-induced transparency in ruby. This field of research has burgeoned in the last 10 years, starting with the work of L Vestergaard Hau and coworkers on slow light via electromagnetically induced transparency in a Bose–Einstein condensate [3]. Many groups are now able to slow light down to a few metres per second or even stop the motion of light entirely [4]. Today, slow light – or more often `slow and fast light' – has become its own vibrant field with a strongly increasing number of publications. In broad scope, slow light research can be categorized in terms of the sort of physical mechanism used to slow down the light. One sort of slow light makes use of material dispersion. This dispersion can be the natural dispersion of the ordinary refractive index or can be the frequency dependence of some nonlinear optical process, such as electromagnetically induced transparency, coherent population oscillations, stimulated light scattering, or four-wave mixing processes. The second sort of slow light makes use of the wavelength dependence of artificially structured materials, such as photonic crystals, optical waveguides, and collections of microresonators. Material systems in which slow light has been observed include metal vapours, rare-earth-doped materials, Raman and Brillioun gain media, photonic crystals, microresonators and, more recently, metamaterials. A common feature of all of these schemes is the presence of a sharp single resonance or multiple resonances produced by an atomic transition, a resonance in a photonic structure, or in a nonlinear optical process. Current applications of slow light include a series of attractive topics in optical information processing, such as optical data storage, optical memories, quantum information devices, and optical communication systems in which the use of slow light will allow all-optical processing with less wasted heat. To implement these applications, devices such as buffers, memories, interferometers and switches that utilize slow light need to be developed. Future challenges include the need for improved coupling of light into slow light modes, overcoming propagation losses, and mitigating the influence of large dispersion of the group velocity. The collection of papers in this special issue of Journal of Optics features a broad spectrum of articles that highlight actual developments in many of the material types and schemes described above. It represents therefore an excellent up to date snapshot of the current state of the field of slow light research. References [1] Lorentz H A 1880 Uber die Beziehung zwischen der Fortpflanzung des Lichtes und der Körperdichte Wiedemann Ann. 9 641–64 [2] McCall S L and Hahn E L 1967 Self-induced transparency by pulsed coherent light Phys. Rev. Lett. 18 908–11 [3] Vestergaard Hau L, Harris S E, Dutton Z and Behroozi C H 1999 Nature 397 594 [4] Philips D F, Fleischhauer A, Mair A, Walsworth R L and Lukin M D 2001 Storage of light in atomic vapor Phys. Rev. Lett. 86 783–6
Electromagnetic pulse propagation in the slow light regime and near a zero group velocity point is relevant to a plethora of potential applications, and has analogies in numerous other wave systems. Unfortunately, the standard frequency-based formulation for pulse propagation is unsuitable for describing the dynamics in such regimes, due to the divergence of the dispersion coefficients. Moreover, in the presence of absorption, it is not clear how to interpret the propagation dynamics due to the drastic change induced by absorption upon the dispersion curves. As a remedy, we present an alternative momentum-based formulation, which is rapidly converging in these regimes, and naturally suitable for lossy and nonlinear media. It is specialized to a waveguide geometry which provides a significant simplification with respect to existing momentum-based schemes. Doing so, we provide a somewhat alternative, yet intuitive picture of the seeming enhanced absorption and nonlinear response in these regimes, and show that light-matter interactions are not enhanced in the slow/stopped light regimes.
Summary form only given. Slow light has been explored for building quantum networks, with particular interest in slowing the group velocity of single photons [1], and more recently exploited to enhance the measurement of small phase shifts. Generally, slow-light effects have been characterized as the net effect of a pulse propagating through the slow-light medium, i.e., as a pulse delay time Δt measured with a fast photodiode at the output of the medium [2]. In this work, we use a single-photon imaging camera to observe slow light in situ, and thus provide a direct measurement of spatial pulse compression and temporal dispersion as the pulse travels through the slow light medium, in this case a hyperfine absorption doublet in hot Rb vapor. Our method combines light-in-flight imaging techniques with a camera comprised of an array of single-photon avalanche diodes (SPAD camera) [3] to image the photons scattered by the Rb vapor in the direction of the camera as shown in Fig. 1(a). In addition, the single photon nature of the SPAD detector allows us to obtain a measurement of the single photon group velocity. As shown in Fig. 1(c) and (d), we observe a significant delay, on the order of nanoseconds, in the detection of the photons scattered when the pulse first enters the slow-light medium. This lag in scattered-photon arrival time is a direct visualization of the slowing down of the single-photon group velocity. The pulses used here had a temporal full width at half maximum (FWHM) of τ ~1 ns, with measured group velocities as low as vg~ 0.006c. At these low group velocities we observe a full fractional pulse delay of up to F D = Δt/τ ~ 40 over 7 cm of propagation, and F D ~ 5 for the scattered single photons, which propagate through ~ 1 cm of Rb vapor prior to exiting the cell en-route to the camera.