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arXiv:1509.08776 · Optics Express

Coherent control of group index and magneto-optical anisotropy in a multilevel atomic vapor

Andreas Lampis, Robert Culver, Balázs Megyeri, J. Goldwin

Published Jun 29, 2016• 20 citations
arXivHTMLPDF

Abstract

We study electromagnetically induced transparency (EIT) in a heated potassium vapor cell, using a simple optical setup with a single free-running diode laser and an acousto-optic modulator. Despite the fact that the Doppler width is comparable to the ground state hyperfine splitting, transparency windows with deeply sub-natural line widths and large group indices are obtained. A longitudinal magnetic field is used to split the EIT feature and induce magneto-optical anisotropy. Using the beat note between co-propagating coupling and probe beams, we perform a heterodyne measurement of the circular dichroism (and therefore birefringence) of the EIT medium. The observed spectra reveal that lin‖lin polarizations lead to greater anisotropy than lin⊥lin. A simplified ‖analytical model encompassing sixteen Zeeman states and eighteen Λ subsytems reproduces the experimental observations.

DOI
10.1364/oe.24.015494

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Steep dispersion and coherent control of Faraday rotation in a potassium vapor cell

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Electromagnetically induced transparency (EIT) was studied in a heated vapor cell of potassium without buffer gas or anti-relaxation coating. Transparency windows 60 times narrower than the natural line width and group indices exceeding 6000 were generated using a simple optical setup with a single free-running laser and an acousto-optic modulator. A longitudinal magnetic field was used to split the EIT feature into three components for either lin$\perp$lin or lin$\parallel$lin polarizations of probe and coupling beams. Measurements of polarization rotation revealed that only the lin$\parallel$lin configuration leads to circular birefringence, an effect which we attribute to quantum interference between the multiple $\Lambda$-type subsystems contributing to the signal. The Verdet constant of the EIT medium was measured to be $(5.8\pm 0.3)\times 10^4$ rad/T/m, and a novel measurement of group index for circular polarization based on birefringence was demonstrated. For larger fields, where the individual peaks were well resolved, resonant polarization rotations of $(210\pm10)$ mrad/MHz were observed.

•Sep 29, 2015•0 citations

Electromagnetically Induced Transparency in Potassium Vapors: Features and Restrictions

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Features of electromagnetically induced transparency (EIT) in potassium vapors at the D 1 line of the 39 K isotope are studied. EIT resonances with a subnatural width of 3.5 MHz have been recorded upon excitation by two independent narrow-band diode lasers in a 1-cm-long cell filled with a natural mixture of potassium isotopes and buffer gas. The splitting of EIT resonances in potassium vapors in longitudinal and transverse magnetic fields has been studied for the first time. The splitted components also have a subnatural width. The smallness of the coupling factor of the hyperfine structure in 39 K atoms leads to a transition to the Paschen—Back regime at relatively weaker magnetic fields than in the case of Cs, Rb, and Na atoms. Practical applications of the phenomena under study are noted. The theoretical model well explains the experiment.

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Coherent light-matter interactions with potassium atoms

Andreas Lampis

This thesis presents experimental work undertaken towards realising a system composed of magneto-optically-trapped potassium-39 atoms (39K MOT) enclosed in a ring cavity. The length of the cavity is 9.51 (5) cm and consequently its volume is big compared to cavities used for cavity quantum electrodynamics experiments, operating in the single-atom regime. As such, in order to enter a regime where the light-matter interactions are strong, thousands of atoms have to collectively interact with the mode of the cavity. We achieve strong interactions with potassium atoms for the first time, after 4.36(3) x 104atoms were overlapped with the cavity mode. The signature of our system lying in the collective strong coupling regime was the observation of the splitting and avoided crossing of the normal modes, revealing a coupling strength constant G = 2π x 19.1(1.6) MHz. \n \nThe thesis also discusses the application of the eltectromagnetically-induced transparency (EIT) technique to control the group index of refraction (ng) of atomic ensembles. We firstly apply EIT in the Λ configuration, in a heated vapour cell of potassium. This helped us to better understand the underlying fundamentals of the technique, before ultimately applying it in the (main) cold atoms experiment. Deeply sub-natural EIT features have been achieved, for which we calculate ng as high as 6330(160). Furthermore, by performing a novel measurement of the circular dichroism (and thus birefringence). We observed greater anisotropy when the weak probe and strong coupling beams, which participate in the formation of the EIT system. have lin∥ lin rather than \nlin ⊥ linpolarisation. \n \nBy optimising the temperature and optical depth of the 39K MOT, EIT investigations were made possible with the cold atoms. While a splitting of the absorption line was observed at high coupling beam powers, no EIT resonances were observed when the coupling power was reduced. Our measurements imply that the EIT signal is compromised by decoherence factors, such as the inhomogeneity of the magnetic field across the atomic cloud. Eliminating decoherence and achieving EIT in the strongly interacting atom-cavity system will enable studies with applications in metrology and sensing.

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Abstract We study Λ-type Electromagnetically Induced Transparency (EIT) on the Rb D2 transition in a buffer-gas-free thermal vapor cell without anti-relaxation coating. Experimental data show well-resolved features due to velocity-selective optical pumping and one EIT resonance. The Zeeman splitting of the EIT line in magnetic fields up to 12 Gauss is investigated. One Zeeman component is free of the first-order shift and its second-order shift agrees well with theory. The full width at half maximum (FWHM) of this magnetic-field-insensitive EIT resonance is reduced due to Doppler narrowing, scales linearly in Rabi frequency over the range studied, and reaches about 100 kHz at the lowest powers. These observations agree with an analytic model for a Doppler-broadened medium developed in (Javan et al 2002 Phys. Rev. A 66 013805; Lee et al 2003 Appl. Phys. B, Lasers Opt. (Germany) B 76, 33–9; Taichenachev et al 2000 JETP Lett. 72, 119). Numerical simulation using the Lindblad equation reveals that the transverse laser intensity distribution and two Λ-EIT systems must be included to fully account for the measured line width and line shape of the signals. Ground-state decoherence, caused by effects that include residual optical frequency fluctuations, atom-wall and trace-gas collisions, is discussed.

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Electromagnetically induced transparency of 87 Rb in a buffer gas cell with magnetic field

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Abstract We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87 Rb vapor at room temperature in a magnetic field with an arbitrary angle to the laser propagation direction. Rather than exposing atoms to a parallelled or transverse magnetic field as usual, in our work, we apply a magnetic field (up to 45 Gauss) with an arbitrary angle to the laser propagation direction and the spectra become much more complex. More EIT dips are observed due to the Zeeman splitting on the D 2 line of 87 Rb in a Λ -type configuration. With a 5 Torr N 2 buffer gas in the thermal 2 cm vapor cell, the state 5 2 P 3 / 2 has a very short effective lifetime, corresponding to a large energy broadening, which removes the velocity selective optical pumping effect almost completely and keeps the high resolution EIT spectrum for the energy splitting of 87 Rb in magnetic fields. The shifting of the EIT resonances with the strength of the applied magnetic field coincides well with the theory based on a full matrix Hamiltonian combined with a spectral decomposition method. Our work can be extended to measure the magnetic field vector in space. The effects of the detuning of the probe and coupling beams on the spectral lines are also investigated.

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Electro-magnetically induced transparency in a static magnetic field

Xiaogang Wei, Jin-Yue Gao, Jin‐Hui Wu +5 more

We investigate both theoretically and experimentally the electro- magnetically induced transparency (EIT) phenomenon of atomic 87Rb at the room temperature with a static magnetic field lifting the degeneracy of all three involved hyperfine levels. Two collinearly propagating and linearly polarized laser fields (a probe field and a coupling field) are used to couple one hyperfine level (the upper level) of the 5P1/2 state to two hyperfine levels (the lower levels) of the 5S1/2 state, respectively. In the case of zero magnetic fields, we observed a deep EIT window with the contrast of about 66%. Here, the EIT window width is limited by both the spontaneous decay rate of the upper level and the coupling field intensity. When a magnetic field parallel to both laser beams is applied, the EIT window is split into three much narrower sub-windows with contrasts of about 32%. If the magnetic field is perpendicular to the laser beams, however, the EIT window is split into four much narrower sub-windows whose contrasts are 32% or 16%. This is because the decomposition of the linearly polarized optical fields strongly depends on the orientation of the used magnetic field. The underlying physics is that, in the limit of a weak probe field, an ideal degenerate three-level system can be split into three or four sets of independent three-level systems by a magnetic field due to the lifting of magnetic sublevels of the involved hyperfine levels. In this paper the absorption spectra corresponding to different magnetic field directions are clearly shown and compared. And a straightforward but effective theoretical method for analyzing the experimental results is put forward. Our theoretical calculations are in good agreement with the experimental results.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Feb 9, 2006•0 citations
We study electromagnetically induced transparency (EIT) in a heated potassium vapor cell, using a simple optical setup with a single free-running diode laser and an acousto-optic modulator. Despite the fact that the Doppler width is comparable to the ground state hyperfine splitting, transparency windows with deeply sub-natural line widths and large group indices are obtained. A longitudinal magnetic field is used to split the EIT feature and induce magneto-optical anisotropy. Using the beat note between co-propagating coupling and probe beams, we perform a heterodyne measurement of the circular dichroism (and therefore birefringence) of the EIT medium. The observed spectra reveal that lin‖lin polarizations lead to greater anisotropy than lin⊥lin. A simplified ‖analytical model encompassing sixteen Zeeman states and eighteen Λ subsytems reproduces the experimental observations.
Electromagnetically induced transparency (EIT) was studied in a heated vapor cell of potassium without buffer gas or anti-relaxation coating. Transparency windows 60 times narrower than the natural line width and group indices exceeding 6000 were generated using a simple optical setup with a single free-running laser and an acousto-optic modulator. A longitudinal magnetic field was used to split the EIT feature into three components for either lin⊥\perp⊥lin or lin∥\parallel∥lin polarizations of probe and coupling beams. Measurements of polarization rotation revealed that only the lin∥\parallel∥lin configuration leads to circular birefringence, an effect which we attribute to quantum interference between the multiple Λ\LambdaΛ-type subsystems contributing to the signal. The Verdet constant of the EIT medium was measured to be (5.8±0.3)×104(5.8\pm 0.3)\times 10^4(5.8±0.3)×104 rad/T/m, and a novel measurement of group index for circular polarization based on birefringence was demonstrated. For larger fields, where the individual peaks were well resolved, resonant polarization rotations of (210±10)(210\pm10)(210±10) mrad/MHz were observed.
Features of electromagnetically induced transparency (EIT) in potassium vapors at the D 1 line of the 39 K isotope are studied. EIT resonances with a subnatural width of 3.5 MHz have been recorded upon excitation by two independent narrow-band diode lasers in a 1-cm-long cell filled with a natural mixture of potassium isotopes and buffer gas. The splitting of EIT resonances in potassium vapors in longitudinal and transverse magnetic fields has been studied for the first time. The splitted components also have a subnatural width. The smallness of the coupling factor of the hyperfine structure in 39 K atoms leads to a transition to the Paschen—Back regime at relatively weaker magnetic fields than in the case of Cs, Rb, and Na atoms. Practical applications of the phenomena under study are noted. The theoretical model well explains the experiment.
This thesis presents experimental work undertaken towards realising a system composed of magneto-optically-trapped potassium-39 atoms (39K MOT) enclosed in a ring cavity. The length of the cavity is 9.51 (5) cm and consequently its volume is big compared to cavities used for cavity quantum electrodynamics experiments, operating in the single-atom regime. As such, in order to enter a regime where the light-matter interactions are strong, thousands of atoms have to collectively interact with the mode of the cavity. We achieve strong interactions with potassium atoms for the first time, after 4.36(3) x 104atoms were overlapped with the cavity mode. The signature of our system lying in the collective strong coupling regime was the observation of the splitting and avoided crossing of the normal modes, revealing a coupling strength constant G = 2π x 19.1(1.6) MHz. \n \nThe thesis also discusses the application of the eltectromagnetically-induced transparency (EIT) technique to control the group index of refraction (ng) of atomic ensembles. We firstly apply EIT in the Λ configuration, in a heated vapour cell of potassium. This helped us to better understand the underlying fundamentals of the technique, before ultimately applying it in the (main) cold atoms experiment. Deeply sub-natural EIT features have been achieved, for which we calculate ng as high as 6330(160). Furthermore, by performing a novel measurement of the circular dichroism (and thus birefringence). We observed greater anisotropy when the weak probe and strong coupling beams, which participate in the formation of the EIT system. have lin∥ lin rather than \nlin ⊥ linpolarisation. \n \nBy optimising the temperature and optical depth of the 39K MOT, EIT investigations were made possible with the cold atoms. While a splitting of the absorption line was observed at high coupling beam powers, no EIT resonances were observed when the coupling power was reduced. Our measurements imply that the EIT signal is compromised by decoherence factors, such as the inhomogeneity of the magnetic field across the atomic cloud. Eliminating decoherence and achieving EIT in the strongly interacting atom-cavity system will enable studies with applications in metrology and sensing.
Abstract We study Λ-type Electromagnetically Induced Transparency (EIT) on the Rb D2 transition in a buffer-gas-free thermal vapor cell without anti-relaxation coating. Experimental data show well-resolved features due to velocity-selective optical pumping and one EIT resonance. The Zeeman splitting of the EIT line in magnetic fields up to 12 Gauss is investigated. One Zeeman component is free of the first-order shift and its second-order shift agrees well with theory. The full width at half maximum (FWHM) of this magnetic-field-insensitive EIT resonance is reduced due to Doppler narrowing, scales linearly in Rabi frequency over the range studied, and reaches about 100 kHz at the lowest powers. These observations agree with an analytic model for a Doppler-broadened medium developed in (Javan et al 2002 Phys. Rev. A 66 013805; Lee et al 2003 Appl. Phys. B, Lasers Opt. (Germany) B 76, 33–9; Taichenachev et al 2000 JETP Lett. 72, 119). Numerical simulation using the Lindblad equation reveals that the transverse laser intensity distribution and two Λ-EIT systems must be included to fully account for the measured line width and line shape of the signals. Ground-state decoherence, caused by effects that include residual optical frequency fluctuations, atom-wall and trace-gas collisions, is discussed.
Abstract We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87 Rb vapor at room temperature in a magnetic field with an arbitrary angle to the laser propagation direction. Rather than exposing atoms to a parallelled or transverse magnetic field as usual, in our work, we apply a magnetic field (up to 45 Gauss) with an arbitrary angle to the laser propagation direction and the spectra become much more complex. More EIT dips are observed due to the Zeeman splitting on the D 2 line of 87 Rb in a Λ -type configuration. With a 5 Torr N 2 buffer gas in the thermal 2 cm vapor cell, the state 5 2 P 3 / 2 has a very short effective lifetime, corresponding to a large energy broadening, which removes the velocity selective optical pumping effect almost completely and keeps the high resolution EIT spectrum for the energy splitting of 87 Rb in magnetic fields. The shifting of the EIT resonances with the strength of the applied magnetic field coincides well with the theory based on a full matrix Hamiltonian combined with a spectral decomposition method. Our work can be extended to measure the magnetic field vector in space. The effects of the detuning of the probe and coupling beams on the spectral lines are also investigated.
We investigate both theoretically and experimentally the electro- magnetically induced transparency (EIT) phenomenon of atomic 87Rb at the room temperature with a static magnetic field lifting the degeneracy of all three involved hyperfine levels. Two collinearly propagating and linearly polarized laser fields (a probe field and a coupling field) are used to couple one hyperfine level (the upper level) of the 5P1/2 state to two hyperfine levels (the lower levels) of the 5S1/2 state, respectively. In the case of zero magnetic fields, we observed a deep EIT window with the contrast of about 66%. Here, the EIT window width is limited by both the spontaneous decay rate of the upper level and the coupling field intensity. When a magnetic field parallel to both laser beams is applied, the EIT window is split into three much narrower sub-windows with contrasts of about 32%. If the magnetic field is perpendicular to the laser beams, however, the EIT window is split into four much narrower sub-windows whose contrasts are 32% or 16%. This is because the decomposition of the linearly polarized optical fields strongly depends on the orientation of the used magnetic field. The underlying physics is that, in the limit of a weak probe field, an ideal degenerate three-level system can be split into three or four sets of independent three-level systems by a magnetic field due to the lifting of magnetic sublevels of the involved hyperfine levels. In this paper the absorption spectra corresponding to different magnetic field directions are clearly shown and compared. And a straightforward but effective theoretical method for analyzing the experimental results is put forward. Our theoretical calculations are in good agreement with the experimental results.