Electromagnetically induced transparency in cesium vapor with probe pulses on the single-photon level

We perform electromagnetically induced transparency (EIT) experiments in cesium vapor with pulses on the single-photon level for the first time. This was made possible by an extremely large total suppression of the EIT coupling beam by 118 dB mainly due to a newly developed triple-pass planar Fabry-Pérot etalon filter. Slowing and shaping of single-photon light pulses as well as the generation of pulses suitable for quantum key distribution applications and testing of approaches for single photon storage is demonstrated. Our results extend single-photon EIT to the particularly interesting wavelength of the Cs D1 line.     

Structural features of self-action of laser radiation in the electromagnetic induced transparency mode

Structural features of the laser radiation self-focusing dynamics in the electromagnetic induced transparency (EIT) band are studied for an atomic system with a Λ-type energy level diagram. Effective nonlinearity of an EIT medium is manifested primarily as nonlinear dispersion (dependence of the group velocity on the wave amplitude). Qualitative analysis of the dynamics of self-action of laser pulses, which is confirmed by numerical simulation, shows that nonlinear evolution of a 3D wave packet follows the scenario of self-focusing, which serves as the background on which the envelope profile turnover and the formation of a shock wave occur at an advanced rate.     

Two narrow bandwidth photons interfering in an electromagnetically induced transparency （EIT） system

In this paper, we have analysed in detail the quantum interference of the degenerate narrowband two-photon state by using a Mach-Zehnder interferometer, in which an electromagnetically induced transparency （EIT） medium is placed in one of two interfering beams. Our results clearly show that it is possible to coherently keep the quantum state at a single photon level in the EIT process, especially when the transparent window of the EIT medium is much larger than the bandwidth of the single photon. This shows that the EIT medium is possibly a kind of memory or repeater for the narrowband photons in the areas of quantum communication and quantum computer. This kind of experiment is feasible within the current technology.     

Ultracold Rydberg atoms for efficient storage of terahertz frequency signals using electromagnetically induced transparency

Quantum communication with terahertz (THz) frequency signals has many advantages like reduced attenuation and scintillation effects in certain atmospheric conditions along with very high level of data security. In this work, we propose a scheme to realize Quantum Memory (QM) for efficient storage of terahertz (THz) frequency signals using Electromagnetically Induced Transparency (EIT) in an ultracold atomic medium of ⁸⁷Rb Rydberg atoms prepared in a Two Dimensional Magneto Optical Trap (2D-MOT). The uniqueness of our scheme lies in the choice of the energy levels involved in the EIT process, all three of which have been chosen to be the Rydberg levels (enabling signal beam to be in THz) in a lambda type arrangement. This first of its kind proposal reveals that atomic media are a potential candidate for devising QMs which can store THz frequency signals. We have estimated that the Optical Depth (OD) in our scheme can reach a very high value of 690, very high maximum obtainable storage efficiency (η) of ～99%, the group velocity ($v_g$) can be as low as 5.07 × 10³ m/s, and the Delay Bandwidth Product (DBP) can be as high as 9.5. All of these estimates emphasize the feasibility of our scheme as a QM device for efficient storage of THz pulses.     

Controllable shape-matched propagation of two signal beams in a double-Λ atomic ensemble

We study a four-level double-Λ atomic ensemble interacting with two time-dependent signal fields and two stationary control fields. Though, in each Λ channel, a pair of signal and control fields couple resonantly with the two lower levels of atoms, the occurrences of electromagnetically induced transparency (EIT) is affected by the coherence of the four fields. In the discussion of atomic susceptibilities, we show that the quantum coherence between the two lower levels can be either formed or released according to the phase matching of the four fields. We analyze the propagation equation of the two signal fields, and find two characteristic solutions: the stationary transmission wave and the transient decay wave. The former corresponds to a correlated EIT effect in which two signal pulses are shape-matched. The latter is an opposite effect to the correlated EIT in which two pulses quench simultaneously, thus named as the correlated two-signal absorption (CTSA). We propose the CTSA condition in correspondence with the EIT condition. The numerical simulation shows that the double-Λ configuration is capable of manipulating synchronous optical signals and thus provides multiplicity and versatility in quantum information process.     

Enhanced frequency conversion of nonadiabatic pulses in a double Λ system driven by two pumps with and without carrier beams

We show that nonadiabatic, resonant amplitude- and phase-modulated pulses can be frequency converted with greater efficiency than adiabatic resonant pulses in a double Λ system, interacting with two strong cw beams on one side of the system, and a weak pulsed probe on the other. Indeed, in this double EIT (electromagnetically induced transparency) configuration, conversion efficiencies close to unity, similar to those achieved using highly detuned pulses, can be obtained using highly nonadiabatic resonant pulses. The distance at which the maximum conversion occurs is shorter than in a coherently-prepared Λ system. This counteracts the increased absorption that occurs in the double EIT configuration, so that both produce similar conversion efficiencies. The absorption experienced by matched nonadiabatic pulses in the double EIT system, at all propagation distances, can be overcome by superimposing the nonadiabatic pulses as amplitude modulations on carrier fields. Thus we demonstrate the formation of adiabatons in the double EIT system, and of diabatons in both the coherently-prepared Λ system and the double EIT system. Both the diabatons and adiabatons satisfy pulse-matching conditions. In addition, the asymptotic amplitude of the complementary amplitude modulations is proportional to the ratio of the pump to probe carrier Rabi frequencies, and is the same in each of the configurations.     

基于自发辐射相干实现光学前驱动场

研究一个具有两个靠得足够近激发能级的双Lambda模型, 在矩形脉冲中分离出光学前驱动场. 当耦合场是大失谐时, 该原子系统在自发辐射相干效应的影响下产生一个透明窗口并伴随着陡峭的色散曲线. 因此, 由于透明窗口中的慢光效应可以使光学前驱动场从主脉冲场中分离出来. 另外, 我们通过调控脉冲波形序列研究探测场相位和幅值的累积光学前驱动波. 数值结果表明: 由于累积光前驱动场与脉冲主场的相长干涉大大地提高瞬态脉冲的能量.     

Storage of an Optical Packet in the EIT Medium

Based on the Dark State Polariton (DSP) theory, a full numerical simulation of an optical packet’s trapping and retrieval procedure in the Electromagnetically Induced Transparency (EIT) medium is first presented here by us.     

Study of radiofrequency radiation by means of optical effect of electromagnetically induced transparency

We propose a method of all-optical investigation of radiofrequency (RF) radiation based on the coherent effect of electromagnetically induced transparency (EIT). It is shown that if the atomic coherence is perturbed by an RF field, the shape of probe pulse propagating in a three-level ??-type atomic medium under EIT conditions is modified correspondingly to the temporal structure of the RF pulse. The effect is sensitive to the parameters of the pulse which enables measuring the intensity and the spectrum of the RF pulse. The method can be used for storage and lossless transfer of RF information over long distances using optical pulses.     

High-speed properties of a phase-modulation scheme based on electromagnetically induced transparency

Recently a cross-phase modulation scheme that yields giant Kerr nonlinearities by use of an electromagnetically induced transparency (EIT) was proposed [Schmidt and Imamoglu, Opt. Lett. 21, 1936 (1996)]. We analyze the high-speed properties of this scheme for short-pulse propagation. We discuss the relevant losses in this system and show that for short pulses one-photon losses are dominant. We demonstrate that over the entire bandwidth the attainable phase shift in an EIT scheme with a quasi-cw coupling field is orders of magnitude higher than in a conventional three-level scheme or in EIT schemes, in which matched pulses are used to create the transparency.     

Electromagnetically induced transparency‐based slow and stored light in warm atoms

This paper reviews recent efforts to realize a high‐efficiency memory for optical pulses using slow and stored light based on electromagnetically induced transparency (EIT) in ensembles of warm atoms in vapor cells. After a brief summary of basic continuous‐wave and dynamic EIT properties, studies using weak classical signal pulses in optically dense coherent media are discussed, including optimization strategies for stored light efficiency and pulse‐shape control, and modification of EIT and slow/stored light spectral properties due to atomic motion. Quantum memory demonstrations using both single photons and pulses of squeezed light are then reviewed. Finally a brief comparison with other approaches is presented.     

Controllable beating signal using stored light pulse

We experimentally study the controllable generation of a beating signal using stored light pulses based on electromagnetically induced transparency(EIT) in a solid medium. The beating signal relies on an asymmetric procedure of light storage and retrieval. After storing the probe pulse into the spin coherence under the EIT condition, two-color control fields with opposite detunings instead of the initial control field are used to scatter the stored spin coherence. The controllable beating signal is generated due to alternative constructive and destructive interferences in the retrieved signal intensities. The beating of the two-color control fields is mapped into the beating of weak probe fields by using atomic spin coherence. This beating signal will be important in precise atomic spectroscopy and fast quantum limited measurements.     

Effect of magnetic field on a multi window ladder type electromagnetically induced transparency with 87Rb atoms in vapour cell

In this work, we experimentally study the effect of externally applied magnetic field on a ladder type EIT in a vapour cell consisting of ⁸⁷Rb atoms. The introduction of magnetic field causes the Zeeman splitting of the hyperfine levels of ⁸⁷Rb atoms and hence the number of available windows of transparency increases. We report the observation of nine such windows. Such multi window EIT systems are capable of storing pulses at the different frequencies, corresponding to these windows hence paving the way for realization of multi frequency quantum memories. Also, the total bandwidth of storage is 218.4 MHz which is two orders of magnitude higher than that typically obtained in single window EIT based storage systems. These systems have tremendous applications in the field of speedy transmission of data over a long distance quantum communication channel.     

双光子失谐对慢光和光存储影响的实验研究

利用电磁感应透明(EIT)效应在87Rb热原子气室中进行了慢光和光存储的实验研究,在单光子红失谐650 MHz处测量了双光子失谐对光脉冲延迟和光存储的影响.结果表明:在双光子失谐0—0.5 MHz范围内存在显著的光脉冲延迟和光存储恢复信号,其慢光波形与理论计算结果基本相符;而恢复光脉冲信号随着双光子失谐的变化出现形变,这是由于多个EIT子系统之间的干涉引起的.这一研究结果为连续变量光场在热原子系综中的存储提供了实验参考.     

Low-light-level cross-phase modulation with double slow light pulses

We report on the first experimental demonstration of low-light-level cross-phase modulation (XPM) with double slow light pulses based on the double electromagnetically induced transparency (EIT) in cold cesium atoms. The double EIT is implemented with two control fields and two weak fields that drive populations prepared in the two doubly spin-polarized states. Group velocity matching can be obtained by tuning the intensity of either of the control fields. The XPM is based on the asymmetric M-type five-level system formed by the two sets of EIT. Enhancement in the XPM by group velocity matching is observed. Our work advances studies of low-light-level nonlinear optics based on double slow light pulses.     

Optical control of light propagation in photonic crystal based on electromagnetically induced transparency

A kind of photonic crystal structure with modulation of the refractive index is investigated both experimentally and theoretically for exploiting electromagnetically induced transparency(EIT).The combination of EIT with periodically modulated refractive index medium gives rise to high efficiency reflection as well as forbidden transmission in a threelevel atomic system coupled by standing wave.We show an accurate theoretical simulation via transfer-matrix theory,automatically accounting for multilayer reflections,thus fully demonstrate the existence of photonic crystal structure in atomic vapor.     

Coherent manipulation of light pulses in a multilevel atomic system

We consider the quantum memory process in general multilevel atomic systems with electromagnetically induced transparency (EIT). We discuss the pulse-matching phenomenon in this general EIT scheme. We also review a recent proposal to create tightly localized stationary pulses by using counterpropagating pump fields. The advantages in creating the stationary pulses with the general EIT system are also discussed.     

Electromagnetically induced self-imaging

We study the self-imaging and image-transforming properties of a probe field in a cold atomic medium with electromagnetically induced transparency (EIT). Due to the similarities between the gradient-index medium and the inhomogeneous index distribution of an EIT medium under the conditions of a negative probe detuning and a Gaussian control field, we find based on analytical investigations that there exists a kind of electromagnetically induced self-imaging phenomenon in cold atomic media. Numerical simulations clearly show that electromagnetically induced self-imaging is observable and controllable.     

Full Quantum Theory of Transient-State Electromagnetically Induced Transparency

We develop a full quantum theory of transient-state electromagnetically induced transparency (EIT) in thevapor of three-level A-type atoms interacting with probe and coupling lasers. As applications of the full quantum theory,we show that transient-state EIT medium exhibits normal dispersion and find that group velocities of both coupling andprobe lasers are greatly reduced. It is shown that the group velocity of the probe laser in the transient-state EIT case isequal to that in the adiabatic EIT case and that the coupling laser group velocity in the transient-state EIT is generallyless than that in the adiabatic EIT.     

Coherent effect of triple-resonant optical parametric amplification inside a cavity with injection of a squeezed vacuum field

In theory, we study the quantum tluctuatlons ot tlae suDllarmonlc renecteu nela Irom a ulplc-rc~ulltUtt IdU~ClIClatC optical parametric amplifier （OPA） inside an optical cavity. We discuss two cases, where the linewidth of the harmonic field is either much narrower or broader than the subharmonic field. Since an electromagnetically-induced-transparency （EIT）-like effect can be simulated in a triple-resonant OPA, the output spectra from a triple-resonant OPA with a squeezed vacuum input may simulate the phenomenon of the response of an EIT medium for squeezed states. This scheme can be implemented with present experimental setups.