Vacuum Rabi splitting and intracavity dark state in a cavity-atoms system

Vacuum Rabi splitting and intracavity dark state in a cavity-atoms system

Gessler Hernandez, Jiepeng Zhang, and Yifu Zhu

Department of Physics, Florida International University, Miami, Florida 33199

Abstract

We report experimental measurements of the transmission spectrum of an optical cavity coupled with cold Rb atoms. We observe the multi-atom vacuum Rabi splitting of a composite cavity and atom system. When a coupling field is applied to the atoms and induces the resonant two-photon Raman transition with the cavity field in a Λ type system, we observe a cavity transmission spectrum with two vacuum Rabi sidebands and a central peak representing the intracavity dark state. The central peak linewidth is significantly narrowed by the dark-state resonance and its position is insensitive to the frequency change of the empty cavity.

PACS numbers: 42.50.-p, 42.50.Pq, 42.50.Gy, 32.80.-t, 42.65.-k

Cavity QED studies interactions of atoms and electromagnetic modes of an optical cavity. The most fundamental system consists of a single two-level atom coupled to a single cavity mode [1]. It has been shown that the composite atom-cavity system exhibits a double-peaked transmission spectrum with the peak separation referred to as the vacuum Rabi splitting and determined by the atom-cavity coupling coefficient V g a 02/εωμh = [2-3]. To observe the vacuum Rabi splitting in the optical wavelength range, it needs to have a g value greater or comparable with the decay rates of the cavity and the atomic system, which requires a high finesse cavity with a small mode volume [4]. However, if N atoms collectively interact with the cavity mode, the coupling coefficient becomes V N g a 02/εωμh = and the multi-atom vacuum splitting may then be observed in a cavity with a moderate mode volume and finesse [5-7]. Studies of atom-cavity interactions can be extended to a composite system of an optical cavity and coherently prepared multi-level atoms, in which the atomic coherence and interference in coherently prepared atoms may be enhanced. For example, electromagnetically induced transparency (EIT)/Coherent population trapping (CPT) can be produced in a three-level Λ-type system [8-9], and its manifestation in a cavity-atom system may be useful for a variety of fundamental studies and practical applications. It has been shown that intracavity EIT results in an ultra narrow spectral linewidth, which may be used for frequency stabilization and high-resolution spectroscopic measurements [10]. Experimental studies of coherently prepared hot atoms confined in a cavity have observed the EIT linewidth narrowing [11] and other interesting phenomena such as control of optical multistability [12].

Here we report an experimental study of a cavity-atom composite system consisting of cold Rb atoms confined in the mode volume of a 5 cm long, near confocal optical cavity. The cold atoms are coupled with the cavity mode and an additional coupling laser, which forms a three-level Λ configuration. We measure the cavity transmission spectrum of a weak probe laser mode-matched to the optical cavity. When the

coupling laser is absent, we observe the multi-atom vacuum Rabi splitting. When the coupling laser is turned on and induces a resonant two-photon Raman transition in the composite atom-cavity system, we observe a three-peaked spectrum consisting of two broad sidebands representing the vacuum Rabi splitting and a narrow central peak manifested by the dark-state resonance of the two-photon Raman transition. The central peak has a linewidth smaller than the natural linewidth and the cavity linewidth, and is limited by the laser linewidth in our experiment. The transmission frequency of the central peak is determined by the two-photon Raman resonance and is insensitive to the change of the empty cavity frequency. The experimental results agree with theoretical calculations based on a semiclassical analysis.

(a) (b)

Fig. 1 (a) 85Rb atoms interacting with a coupling field and a cavity field, which forms a three-level Λ-type system. The spontaneous decay rate of the excited state |3> is Γ (=2πx5.4x106 s -1). (b) Schematic drawing of the cavity apparatus. The coupling (probe) laser is linearly polarized along the y (z) direction.

The composite atom-cavity system in our experiment can be viewed as a coupled Λ system shown in Fig. 1a. The standing-wave cavity mode couples the atomic transition |1>-|3> (the 85Rb D1 F=2-F’=3 transition). The coupling field drives the atomic transition |2>-|3> (the 85Rb D1 F=3-F’=3 transition) with Rabi frequency 2? and forms a standard Λ-type configuration. 32νν?=? is the coupling laser-atom

Z y x

detuning, 31νν?=?c c is the cavity mode-atom detuning, and 31νν?=?p p is the probe laser-atom detuning. Under the condition of the two-photon Raman resonance (?=?p ), a dark state is created, which leads to the suppressed light absorption and rapidly varying dispersion near the two-photon resonance [8-9]. When ?=?p =0, the dark state resonance corresponds to the resonant EIT, under which it has been shown that the cavity transmission peak occurs at the resonant frequency [10] η

ηνηνν+++=11p c r . Here νp is the probe laser frequency 21ννν+=p ( ν21 is the frequency separation between the two ground states |1> and |2>) and p

r L νχνη??='2l is a coefficient characterizing the dispersion change near the two-photon Raman resonance (l is the medium length, L is the cavity length, and 'χ is the real part of the medium susceptibility at the probe frequency). The linewidth of the cavity transmission peak is ηκκν+??=?1)

1(1C R R [10]. Here C is the empty cavity linewidth, R is the intensity reflectivity of the cavity mirror, and )/''2exp(c p l χπνκ?=is the single pass medium absorption (''χis the imaginary part of the medium susceptibility at the probe frequency). When η>>1, the linewidth of the cavity transmission peak is reduced by a factor of η relative to the empty cavity linewidth and is ultimately limited by the ground state decoherence rate γ that can be many orders less than the atomic natural linewidth Γ. Also the cavity resonant frequency is essentially independent of the empty cavity frequency and nearly equal to the probe frequency νp .

The experiment is done with cold 85Rb atoms confined in a magneto-optical trap (MOT) produced at the center of a 10-ports stainless-steel vacuum chamber. The MOT is obtained with two extended-cavity diode lasers with a beam diameter of ~ 1 cm: one with output power ~ 30 mW is used as the cooling and trapping laser supplying six perpendicular retro-reflected beams, and another with output power ~15 mW is used as the repump laser. The trapped 85Rb atom cloud is ~ 1.5 mm in diameter and the measured optical depth

nσ13? is ~ 3. A schematic diagram of the cavity apparatus is depicted in Fig. 1(b). The standing-wave cavity consists of two mirrors of 5 cm curvature with a mirror separation of ~ 5 cm and is mounted on an Invar holder enclosed in the vacuum chamber. The empty cavity finesse is measured to be ~ 200. Movable anti-Helmholtz coils are used so the MOT position can be finely adjusted to coincide with the cavity center. A third extended-cavity diode laser with a beam diameter ~ 5 mm and output power ~ 35 mW is used as the coupling laser that propagates along the x direction and directed to overlap with the MOT through a vacuum viewport. A fourth extended-cavity diode laser is used as the probe laser, which is attenuated and split into two parts. One part propagates in the y direction and is coupled into the cavity. The transmitted cavity light passes through an iris and then is collected by a photodiode. Another part of the probe beam propagates nearly parallel to the coupling laser (at an angle of ~3o ) in the same x-y plane, overlaps with the MOT from free space, and is then collected by another photodiode, which provides the probe absorption spectrum in free space and serves as a reference for comparison with the recorded cavity transmission spectrum.

The experiment is run in a sequential mode with a repetition rate of 10 Hz. all lasers are turned on or off by acousto-optic modulators (AOM) according to the time sequence described below. For each period of 100 ms, ~99 ms is used for cooling and trapping of the 85Rb atoms, during which the trapping laser and the repump laser are turned on by two AOMs while the coupling laser and the probe laser are off. The time for the data collection lasts ~ 1 ms, during which the repump laser is turned off first, and after a delay of ~0.15 ms, the trapping laser and the current to the anti-Helmholtz coils of the MOT are turned off, and the coupling laser and the probe laser are turned on. After the coupling laser and probe laser are turned on by the AOMs for 0.1 ms, the probe laser frequency is scanned across the 85Rb D1 F=2→F=3 transitions and the cavity transmission of the probe laser is then recorded versus the probe frequency detuning.

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0.6-100-50050100

(b) ?p (M H z)(a) I o u t /I o u t (e m p t y c a v i t y ) ?p (M H z) Expt. D ata Em pty Cavity Calculation (c)

?p (M H z)

Fig. 2 Cavity transmission versus the probe detuning ?p . Blue (red) lines are experimental data (calculations). The cavity detuning ?c =0. (a) ?=0. (b) ?≈8 MHz and ?≈0. (c) ?≈8 MHz and ?≈-12 MHz. For comparison, the free-space probe spectrum (in an arbitrary scale) is plotted in the top of (b) and (c), in which black (red) lines are experimental data (calculations). The other parameters used in the calculations are n σ13?=2.5, R=0.97, and the ground state decoherence rate γ=0.02 Γ.

Fig. 2 plots the measured cavity transmission of the probe laser (normalized to the peak intensity of the empty-cavity transmission I out(empty cavity)) versus the probe frequency detuning ?p (the empty cavity frequency is tuned to 31νν=c ). Blue lines are experimental data and red lines are calculations based on a semiclassical analysis. For reference, the transmission peak of the empty cavity (no atoms in the cavity) is plotted as the dark line in Fig. 2(a) and its vertical scale is reduced by 2 times. When the coupling laser is turned off (?=0), the cold Rb atoms can be viewed as a two-level system and the cavity transmission is plotted as the blue line in Fig. 2(a). We observe two transmission peaks at ?p =±g. The peak separation represents the multi-atom vacuum Rabi splitting (the normal cavity-atom modes) and is

given by 2g=V N a 02/2εωμh ≈60 MHz, from which we derive that there are ~ 104 atoms in the cavity mode volume of V~7x10-4 cm 3. The measurements were taken at the low power levels of the input probe laser at which the transmitted power of the empty cavity (without atoms) ≤0.1 μW. We observed that at higher probe powers, the line shape of the vacuum Rabi splitting become asymmetrical due to saturation of the intra-cavity field as reported in ref. [7]. When the coupling laser is turned on, the cavity transmission spectrum versus ?p exhibits three peaks: the two vacuum Rabi sidebands at ?p ≈±g and a central peak at ?p =? that represents the dark-state resonance and is narrowed by the dark-state manifested frequency pulling and absorption suppression. The central peak in Fig. 2(b) corresponds to the EIT resonance (?p =?=0). Our measurements show that when ?≠0, the intra-cavity dark state is shifted accordingly and always occurs at the two-photon Raman resonance ?p =?. Fig 2(c) shows the measured spectrum for ?≈-12 MHz, in which the cavity dark-state resonance occurs at ?p =?12 MHz. For comparison, the probe absorption spectra under these conditions in free space are plotted in the top of Fig. 2(b) and 2(c), and show the resonant EIT (?=0, Fig.2(b)) and the off-resonant spectral features (?≈-12 MHz, Fig.2(c)). Our results show that with EIT, the splitting of the two vacuum Rabi sidebands becomes .222?+g In our experiment, g ≈30 MHz and ?≈8 MHz, the EIT and the dark state resonance results in the narrow central peak at ?p =0 for the composite cavity-atom system, but its effect on the vacuum Rabi sidebands is small (the separation of the two vacuum Rabi sidebands in Fig. (2b) differs from that of Fig. (2a) by ~1 MHz). When the coupling laser is detuned from the atomic resonance (?≠0), the measurements show that the frequency pulling induced by the atomic dispersion near the two-photon Raman resonance shifts the cavity resonant frequency νr such that the narrow cavity transmission occurs at the resonant two-photon transition ?p =?≠0 where the intracavity dark state is formed. The linewidth (FWHM) of the intra-cavity

dark state is measured to be ~ 1.2 (±0.4) MHz, which is limited by the laser linewidth (~1 MHz) in our experiment, and is smaller than the Rb natural linewidth (Γ=5.6 MHz) and the empty cavity linewidth (~14 MHz). The experimental measurements agree with the theoretical calculations and the value of η is derived to be ~ 25.

Fig. 3 plots the measured cavity transmission of the probe laser (normalized to the peak intensity of the empty-cavity transmission I out(empty cavity)) versus the probe frequency detuning ?p when the empty cavity frequency c ν is detuned from the atomic transition frequency 31ν (the coupling frequency is kept on resonance (?=0)). It shows that when the cavity is detuned (31νν≠c ), the vacuum Rabi peaks, representing

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0.30.6

-100-500501000.00.30.6(a) I o u t /I o u t (e m p t y c a v i t y ) ?p (MHz)

(b)?p (MHz)

Fig. 3 Cavity transmission versus the probe detuning ?p . Blue (red) lines are experimental data (calculations). The coupling detuning ?=0. (a) ?≈8 MHz and ?c ≈13 MHz. (b) ?≈8 MHz and ?c ≈-5 MHz. The other parameters are the same as those in Fig . 2.

the normal modes of the coupled cavity-atoms system, shift in their positions and have unequal amplitudes, but the narrow central peak is always located near ?p =?=0 where the two-photon Raman transition |1>-|3>-|2> is resonant. T hat is, the intra-cavity dark state is induced by the two-photon Raman resonance, its position is given by ?p =? and is insensitive to the change of the empty cavity frequency .

Under the condition of the two-photon Raman resonance (?p =?), we plot the position of the intra-cavity dark state (the frequency of the central transmission peak) versus the coupling frequency detuning ? in Fig.

νr -ν31 (M H z )?=?p (MHz)

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νr -νp (M H z )?c (MHz)

Fig. 4 Resonant frequency of the intra-cavity dark state versus (a) the frequency detuning ?=?p and (b) the frequency detuning ?c of the empty cavity. Lines are the calculations and dots are experimental data. For (a), the empty cavity frequency is tuned to the atomic transition frequency ν31 (?c =0). For (b), the probe and the coupling detunings are kept at ?p =?=0.

Fig. 4(a) and also versus the empty cavity detuning ?c in Fig. 4(b). The experimental data are plotted as solid dots and the calculated results for several η values are plotted in solid lines. The experimental measurements demonstrate that the cavity resonant frequency νr (the intracavity dark-state resonance) is nearly equal to the probe frequency νp at the two-photon Raman resonance (Fig. 4(a)) and is insensitive to the frequency change of the empty cavity (Fig. 4(b)). Such characteristic of the coupled cavity-atom system is useful for the frequency standard and atomic clocks based on EIT/ CPT [13]. There are two advantages of a cavity-atom composite system for such applications: first, a strong coupling field can be used to create a large EIT/CPT window, which increases the signal to noise ratio but does not cause the power broadening

of the cavity transmission; second, the cavity transmission peak is always kept on the two-photon Raman resonance ?p=? and is insensitive to changes of the empty cavity frequency caused by the cavity length drift due to the thermal and mechanical instabilities.

In conclusion, we have measured the transmission spectrum of an optical cavity coupled with coherently prepared cold Rb atoms. When the intra-cavity dark state is induced by a coupling laser in the cavity and Λ-type atomic system, the cavity transmission spectrum exhibits three peaks: two sidebands associated with the multi-atom vacuum Rabi splitting and a narrow central peak representing the cavity dark-state resonance. The experimental results agree with the theoretical results of ref. [10] for the resonant EIT at ?p=?=0 and also show that they can be extended to the detuned Λ system without EIT as long as the two-photon Raman resonance is satisfied. The cavity-atom composite system can be used for a variety of fundamental studies [14]and may be useful for the EIT/CPT based precision measurement applications [13,15].

This work is supported by the National Science Foundation under Grant No. 0456766.

References

1. E. T. Jaynes and F. W. Cummings, Proc. IEEE 51, 89(1963).

2. J. J. Sanchez-Mondragon, N. B. Narozhny, and J. H. Eberly, Phys. Rev. Lett. 51, 550(1983).

3. Cavity Quantum Electrodynamics, edited by P. R. berman (Academic, San Diego, 1994).

4. A. Boca, R. Miller, K. M. Birnbaum, A. D. Boozer, J. McKeever, and H. J. Kimble, Phys. Rev. Lett. 93, 233603 (2004).

5. G. S. Agarwal, Phys. Rev. Lett. 53, 1732(1984).

6. Y. Zhu, D. J. Gauthier, S. E. Morin, Q. Wu, H. J. Carmichael, and T. W. Mossberg, Phys. Rev. Lett. 64, 2499 (1990).

7. J. Gripp, S. L. Mielke, and L. A. Orozco, Phys. Rev. A 56, 3262(1997).

8. S. E. Harris, Phys. Today 50, 36 (1997).

9. E. Arimondo, in Progress in Optics (E. Wolf ed.) Vol. 31, 257(1996).

10. M. D. Lukin, M. Fleischhauer, M. O. Scully, and V. L. Velichansky, Opt. Lett. 23, 295 (1998).

11. H. Wang, D. J. Goorskey, W. H. Burkett, and M. Xiao, Opt. Lett. 25, 1732 (2000).

12. A. Joshi and M. Xiao, Phys. Rev. Lett. 91, 143904 (2003).

13. S. Knappe, V. Shah, P. Schwindt, L. Hollberg L, J. Kitching , L. A. Liew , J. Moreland, Appl. Phys. Lett. 85, 1460 (2004).

14. J. Ye and T. W. Lynn, in Advances in Atomic, Molecular, and Optical Physics, edit. by B. Bederson and H. Walther, Vol. 49, p1 (2003).

15. P. Schwindt, S. Knappe S, V. Shah, L. Hollberg, J. Kitching, L. A. Liew, and J. Moreland, Appl. Phys. Lett. 85, 6409(2004).

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镀膜真空术语全集（中英文对照） 5.分压真空计（分压分析器） 5-1.射频质谱仪radio frequency mass spectrometer： 5-2.四极质谱仪（四级滤质器）quadrupole mass spectrometer；quadrupole mass filer：5-3.单极质谱仪momopole mass spectrometer： 5-4.双聚焦质谱仪double focusing mass spectrometer： 5-5.磁偏转质谱仪magnetic deflection mass spectrometer： 5-6.余摆线聚焦质谱仪trochoidal focusing mass spectrometer： 5-7.回旋质谱仪omegatron mass spectrometer： 5-8.飞行时间质谱仪time of flight mass spectrometer： 6.真空计校准 6-1.标准真空计reference gauges： 6-2.校准系统system of calibration： 6-3.校准系数K calibration coefficient： 6-4.压缩计法meleod gauge method： 6-5.膨胀法expansion method： 6-6.流导法flow method： 4. 1.真空系统vacuum system 1-1.真空机组pump system： 1-2.有油真空机组pump system used oil ： 1-3.无油真空机组oil free pump system 1-4.连续处理真空设备continuous treatment vacuum plant： 1-5.闸门式真空系统vacuum system with an air-lock： 1-6.压差真空系统differentially pumped vacuum system： 1-7.进气系统gas admittance system： 2.真空系统特性参量

真空计(vacuum gauge)介绍

真空计(vacuum gauge)介绍 用于测量低于大气压的稀薄气体总压力的仪表，又称真空规。真空计的测量单位沿用压力测量单位，压力的国际单位为帕(Pa)，曾使用的单位还有托(Torr)和毫巴(mbar)等。 自1643年意大利物理学家E.托里拆利进行大气压力实验以来，先后出现许多种真空计。最早出现的是Ｕ形管真空计,它只能用来测量粗真空和低真空。1874年,H.G.麦克劳发明的压缩式真空计,解决了低真空和高真空的绝对压力的测量，但仍不能进行连续测量。1906年，M.皮喇尼发明电阻式真空计，解决了工业生产中的低真空测量问题。继而，O.E.巴克利于1916年又发明电离真空计,这在当时不仅解决了10-1～10-5帕的高真空测量,而且促进了油扩散泵等真空设备的发展和应用。1937年，F.M.潘宁发明冷阴极电离真空计，适用于有大量放气和经常暴露于大气的真空设备的测量，所以在真空冶金和机械工业中得到广泛应用。1950年，R.T.贝阿德和D.A.阿尔伯特发明BA式电离真空计,解决了10-8帕的超高真空测量问题,从而使真空测量获得了突破,并推动了超高真空技术的发展；而与此有关的表面物理、核能、航天和大型集成电路等科学技术也得到了迅速发展。1960年以来，相继研制成功的调制规、抑制规、弯注规、分离规和磁控式电离规等已能实现10-11帕左右的超高真空测量。 分类真空计可分为绝对真空计和相对真空计两大类。凡能从其本身测得的物理量（如液柱高度、工作液、比重等）直接计算出气体压力的称绝对真空计，这种真空计测量精度较高，主要用作基准量具。相对真空计主要利用气体在低压力下的某些物理特性（如热传导、电离、粘滞性和应变等）与压力的关系间接测量，其测量精度较低，而且测量结果还与被测气体种类和成分有关。因此相对真空计必须用绝对真空计标定和校准后方能用作真空测量。但它能直接读出被测压力，使用方便，在实际应用中占绝大多数。真空技术需要测量的压力范围为105～10-11帕，甚至更小,宽达16个数量级以上,尚无一种真空计能适用于从粗真空(105～102帕)、低真空（102～10-1帕）、高真空（10-1～10-5帕）、超高真空（小于10-5帕）到极高真空（小于10-10帕）的全范围测量,因而有多种真空计。最常用的有U形管真空计、压缩式真空计、电阻真空计和冷热阴极电离真空计。 U形管真空计用以测量粗真空和低真空的绝对真空计。在U字形的玻璃管中充以工作液（低蒸气压的油、汞）。管的一端被抽成真空（或直接通大气），另一端接被测真空系统。根据两边管中的压差所造成的液柱差可测出被测真空系统的压力。 压缩式真空计又称麦克劳真空计，是一种测量低真空和高真空的绝对真空计。这种真空计一般用硬质玻璃制成。A是一根与被测真空系统相连接的开管，D、B为内径相同的毛细管，V为球泡,其体积远大于毛细管。测量时，通过活塞2抽真空，然后用活塞1充气,使汞储存器C中的汞上升到覆没交叉口ΜΜ′，则D、V和B、A内的气体被隔成两个区域。再充气继续提高汞液面,D、V内的气体则进一步被压缩，压力增高。这样D、B间存在的压差可由汞柱高度差来表示。玻璃容器的体积和毛细管的高度是可精确测出的，所以用玻意耳定律即可算出被测压力。测量精度较高,在10-3帕时的精度小于或等于5％。 电阻真空计又称皮喇尼真空计，是一种测量低真空的相对真空计，主要由电阻式规管和测量线路两部分组成。电阻式规管是在管壳内封装着一条电阻温度系数较大的电阻丝，常用的为钨或铂丝。测量时，规管与被测真空系统相接，用一定的电压、电流加热电阻丝，其表面温度可用电阻值来反映，且与周围的气体分子的热传导有关，而气体分子的热传导又与压力有关。当被测压力降低时，由气体分子传走的热量减小，电阻丝表面温度就增高，电阻值增大；反之，电阻值减小。因此根据电阻值的大小就可测量出压力。 热阴极电离真空计通称电离真空计，主要用于高真空测量。它是由圆筒式热阴极电离规管和测量线路两部分组成。这种规管与三极电子管相似，有 3个电极：阴极（灯丝）、螺旋