Atomic qubit manipulations with an electro-optic modulator

We report new techniques for driving high-fidelity stimulated Raman transitions in trapped-ion qubits. An electro-optic modulator induces sidebands on an optical source, and interference between the sidebands allows coherent Rabi transitions to be efficiently driven between hyperfine ground states separated by 14.53 GHz in a single trapped 111Cd+ ion.     

用于铯原子内态操控的双光子拉曼激光的产生及应用

双光子拉曼过程是一种有效制备和控制原子内态的方法, 在原子内态操控和基于原子的量子信息处理中具有重要意义. 研制用于特定原子的拉曼激光是实现该过程的重要一步. 报道了利用光纤波导相位调制器及滤波器等实现用于铯原子内态操控的拉曼激光的方法, 并成功用于单个铯原子的内态精密操控. 通过4.6 GHz的微波信号源直接驱动波导相位调制器高效地获得光场的调制边带, 并利用自由光谱区为9.19 GHz的法布里-珀罗腔将载波及二阶边带滤掉, 获得了频率精确、相差9.19 GHz的拉曼激光. 经过基于光纤振幅调制器的功率稳定系统, 最终可以获得总功率为73 μupW、长时间内波动为2.2%的拉曼激光束, 并将此光束用于激发单个铯原子, 实现了|6S_1/2, F=4, mF=0和|6S_1/2, F=3, mF=0 之间的可控拉比操作.     

A frequency-doubled laser system producing ns pulses for rubidium manipulation

We have constructed a pulsed laser system for the manipulation of cold ⁸⁷Rb atoms. The system combines optical telecommunications components and frequency doubling to generate light at 780 nm. Using a fast, fibre-coupled intensity modulator, we sliced output from a continuous laser diode into pulses with a length between 1.3 and 6.1 ns and a repetition frequency of 5 MHz. These pulses are amplified using an erbium-doped fibre amplifier, and frequency-doubled in a periodically poled lithium niobate crystal, yielding a peak power up to 12 W. Using the resulting light at 780 nm, we demonstrate Rabi oscillations on the F=2,m_F=+2↔F^′=3, m^′ _F=+3-transition of a single ⁸⁷Rb atom. PACS 32.80.Qk; 39.25.+k; 42.55.-f     

Spectral line suppression and sideband narrowing via quantum interference

We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states.     

Generating controllable atom-light entanglement with a Raman atom laser system

We introduce a scheme for creating continuous variable entanglement between an atomic beam and an optical field, by using squeezed light to outcouple atoms from a Bose-Einstein condensate via a Raman transition. We model the full multimode dynamics of the atom laser beam and the squeezed optical field and show that, with appropriate two-photon detuning and two-photon Rabi frequency, the transmitted light is entangled in amplitude and phase with the outcoupled atom laser beam. The degree of entanglement is controllable via changes in the two-photon Rabi frequency of the outcoupling process.     

光学相位锁定激光在原子玻色-爱因斯坦凝聚中实现拉曼耦合

采用光学相位锁定环路技术将外腔反馈式半导体激光器锁定到与钛宝石激光器输出激光频率上. 锁定后两束激光的差频线宽从MHz降低到Hz量级, 同时两束激光的频率差可实现几百兆赫兹到7 GHz的精密调节. 锁定的两束激光作用在铷原子玻色-爱因斯坦凝聚的两个基态超精细态F=2, 1, 观测到在两个超精细态之间的拉曼跃迁. 该技术可用于超冷原子两个超精细态之间自旋轨道耦合.     

Multi-photon processes in the Zeeman structure of atomic Cs trapped in solid helium

We report magnetic resonance experiments with optical detection performed on cesium atoms trapped in a crystalline ^Hematrix. Multi-photon transitions, i.e., processes in which several radio-frequency photons are absorbed simultaneously in a given hyperfine Zeeman multiplet of the ground state, were the central topic of these studies. The long relaxation times of spin coherences of Cs in solid He allow such transitions to be spectrally resolved in fields as low as 1 mT. We observed all allowed multi-photon transitions up to the M=8 transition in the F=4 state. We compare the experimental spectra with theoretical spectra obtained from numerical solutions of the Liouville equation that include optical pumping and the interaction with the static and oscillating fields. Multi-photon transitions may find applications in magnetometry, suppress systematic effects in EDM experiments, and allow the study of relaxation phenomena in doped He crystals. The demonstration of these features is still hindered by inhomogeneous line broadening. PACS 76.70.Hb; 32.80.Wr; 32.30.Dx; 32.60.+i     

弱射频场中Rydberg原子的电磁感应透明

在铯原子室温蒸气池中研究了弱射频场中Rydberg原子阶梯型三能级系统的电磁感应透明(EIT)效应.铯原子基态6S_(1/2)、第一激发态6P_(3/2)和Rydberg 48D_(5/2)态形成阶梯型三能级系统,探测光共振作用于6S_(1/2)(F=4)→6P_(3/2)(F′=5)的跃迁,耦合光在Rydberg跃迁线6P_(3/2)(F′=5)→48D_(5/2)附近扫描,形成Rydberg原子EIT.当对铯原子施加一个80 MHz的弱射频电场时,48D_(5/2)Rydberg原子的EIT光谱发生Stark频移和分裂,同时产生由射频场调制Rydberg能级的偶数级边带,测量结果与Floquet理论模拟的结果相符合.同时,改变弱射频电场的频率研究了铯Rydberg能级的自电离效应对Rydberg原子Stark谱的影响,据此,我们提出将电极板置于铯原子蒸气池内的方案以减少自电离效应的影响.在弱射频Stark谱中,mj=5/2的Stark谱与mj=1/2,3/2的二级边带形成多个能级交叉,这些能级交叉点提供了一种基于原子的精确校准射频电场的新方法.     

铯原子7S1/2态磁偶极超精细常数的测量

在室温下的原子气室中, 基于铯原子6S_1/2-6P_3/2-7S_1/2(852.3 nm+1469.9 nm) 阶梯型能级系统, 利用电光调制器的主频和±1级边带分别产生的三套双共振吸收光谱, 当驱动电光调制器的信号源频率严格等于7S_1/2态超精细分裂的能级间隔时, 三套谱线中的一些超精细跃迁谱线重叠且线宽最窄, 利用这一现象很好地避免了激光器频率扫描时非线性效应的影响, 测量出了7S_1/2 态超精细分裂能级间隔: 2183.72 MHz±0.23 MHz, 并计算出该态的磁偶极超精细常数: A_hfs= 545.93 m MHz±0.06 MHz, 与文献中报道的测量结果一致.     

Fast ground state manipulation of neutral atoms in microscopic optical traps

We demonstrate Rabi flopping at MHz rates between ground hyperfine states of neutral 87Rb atoms that are trapped in two micron sized optical traps. Using tightly focused laser beams we demonstrate high fidelity, site specific Rabi rotations with cross talk on neighboring sites separated by 8 microm at the level of 10(-3). Ramsey spectroscopy is used to measure a dephasing time of 870 micros, which is approximately 5000 longer than the time for a pi/2 pulse.     

Role of the carrier-envelope offset phase of few-cycle pulses in nonperturbative resonant nonlinear optics

We study the influence of the carrier-envelope offset phase of few-cycle pulses on nonperturbative resonant extreme nonlinear optics in a semiconductor. If the Rabi frequency becomes comparable to the light frequency, the different Rabi sidebands interfere around twice the laser center frequency, giving rise to a signal which strongly depends on the carrier-envelope offset phase. This signature should be measurable in GaAs samples.     

用于铯原子受激拉曼绝热输运过程的光源的产生

受激拉曼绝热输运(STIRAP)是一种有效制备和控制原子态的技术,在原子操控和量子信息中具有重要意义,最近几年得到广泛关注.研制用于特定原子的拉曼激光是实现该过程的重要一步.研究了利用光纤波导调制器及干涉滤波器等组成的系统实现用于铯原子STIRAP过程的光源的方法.通过直接调制高频光纤调制器获得正负一级边带,并利用两个...     

超冷铯Rydberg原子的Autler-Townes分裂

主要研究超冷铯Rydberg原子阶梯型三能级系统的Autler-Townes(A-T)分裂.铯原子基态6S_(1/2)、第一激发态6P_(3/2)和Rydberg态形成阶梯型三能级系统,强耦合光共振作用于6P_(3/2)(F′=5)→34D_(5/2)的跃迁,探测光由偏振光谱锁定在6S_(1/2)(F=4)→6P_(3/2)(F′=5)的跃迁,并由双通的声光调制器在其共振跃迁附近扫描,形成的Rydberg原子A-T分裂谱由单光子计数器探测.A-T光谱的双峰间距与耦合光的拉比频率成正比,实验结果与理论计算在耦合光拉比频率Ω_c2π×9 MHz时符合得很好,在拉比频率Ω_c2π×9 MHz时,测量的A-T分裂比理论计算值小13%.产生偏差的主要原因是由于较大的耦合光拉比频率Ω_c增加了激发的Rydberg原子数,Rydberg原子间的相互作用产生了较大的退相干率所致.     

Dressed states analysis of lasing without population inversion in a three-level ladder scheme: Approximate analytic time dependent solutions

A dressed-state study of lasing without population inversion from a three level atom interacting with a bi-chromatic laser field, in the ladder configuration, is formulated. We allow the atomic system to be dressed by both laser filed photons (double dressing). The evolution of the system under consideration is being explored both analytically and numerically, within the transient regime. Time dependent approximate analytic solutions for dressed-state populations and coherences are derived, within the so called “secular approximation,” under resonant conditions. We also present time dependent numerical solutions for population and coherences in the off-resonance regime. A spectral analysis is also performed revealing the structure of various dressed states transitions. These are shown to be composed of quintets centered about the frequencies of the coupling and probe laser fields and having sidebands located symmetrically at positions shifted from line center at the Rabi and double Rabi frequencies.     

飞秒激光场中原子所受光学偶极力研究

通过求解全波矢布洛赫方程研究了两能级原子与飞秒超快激光脉冲的相互作用过程,计算了不同拉比频率取值下原子所受光学偶极力和粒子数布居随时间的演化情况,分析了光场失谐量对光学势分布情况的影响.研究发现:由飞秒激光场产生的横向光力的时间平均值并不等于零,而是随着拉比频率的增加呈现振荡的增大趋势;纵向光力的时间平均作用也并非是拉比频率的单调函数,而是随着拉比频率的增加呈现周期性的振荡分布特性;光学势的分布对光场的失谐量具有明显的依赖性,随着失谐量的变化,光学势的性质也随之发生了改变.     

Observation of Raman forward scattering and electron accelerationin the relativistic regime

Raman forward scattering (RFS) is observed in the interaction of a high intensity (>10¹⁸ W/cm²) short pulse (<1 ps) laser with an underdense plasma (n_e~10¹⁹ cm ^-3). Electrons are trapped and accelerated up to 44 MeV by the high-amplitude plasma wave produced by RFS. The laser spectrum is strongly modulated by the interaction, showing sidebands at the plasma frequency. Furthermore, as the quiver velocity of the electrons in the high electric field of the laser beam becomes relativistic, various effects are observed which can be attributed to the variation of electron mass with laser intensity     

Paramagnetic Faraday rotation with spin-polarized ytterbium atoms

We report the observation of paramagnetic Faraday rotation of spin-polarized ytterbium (Yb) atoms. As the atomic samples, we used an atomic beam, released atoms from a magneto-optical trap (MOT), and trapped atoms in a far-off-resonant trap (FORT). Since Yb is diamagnetic and includes a spin-1/2 isotope, it is an ideal sample for spin physics, such as quantum non-demolition measurement of spin (spin QND), for example. From the results of the rotation angle, we confirmed that the atoms were almost perfectly polarized. PACS 32.80.Bx; 32.80.Pj; 42.25.Lc     

Magnetic-Field Dependence of Raman Coupling Strength in Ultracold ~(40)K Atomic Fermi Gas

We experimentally demonstrate the relation of Raman coupling strength with the external bias magnetic field in degenerate Fermi gas of ~(40)K atoms.Two Raman lasers couple two Zeeman energy levels,whose energy splitting depends on the external bias magnetic field.The Raman coupling strength is determined by measuring the Rabi oscillation frequency.The characteristics of the Rabi oscillation is to be damped after several periods due to Fermi atoms in different momentum states oscillating with different Rabi frequencies.The experimental results show that the Raman coupling strength will decrease as the external bias magnetic field increases,which is in good agreement with the theoretical prediction.     

Selective loading and laser cooling of rare calcium isotope 43Ca+

We report a method for loading ⁴³Ca⁺ ions selectively in a linear Paul trap using ultraviolet light-emitting-diodes (LEDs) for the second excitation in a two-step photo-ionization process. The difficulty in working with ⁴³Ca⁺ is its low natural abundance (0.135%). In order to load ⁴³Ca⁺ selectively, we utilize the isotope shifts for the 4s^{2 1} S ₀–4s4p¹ P ₁ transition of neutral calcium atoms. We discuss the limitation of the selectivity of the employed photo-ionization scheme and observe spectra from unwanted isotopes as well as that from ⁴³Ca⁺. Purification of ⁴³Ca⁺ is performed by adjusting the detuning of the cooling laser frequency and trapping potential. The method of loading and purification can be used in the application of trapped ⁴³Ca⁺ for an optical frequency standard and for quantum information processing. PACS 32.80.Fb; 32.80.Pj     

Study of frequency-modulated excitation of Rydberg potassium atoms by using B-spline

With the B-spline expansion technique and a model potential of the alkali atoms, the properties of frequency-modulated excitation of Rydberg potassium atoms in a static electric field and a microwave field are investigated by using the time-dependent two-level approach. We successfully reproduce the square wave oscillations in the low frequency, the stair step population oscillations in the intermediate frequency, and the multiphoton transitions in the high frequency with respect to the unmodulated Rabi frequency, which have been observed experimentally by Noel et al. [Phys. Rev. A 58 2265 (1998)]. Furthermore, we also numerically obtain the discretized Rabi oscillations predicted in the Landau-Zener accumulation model.