Stationary Light Pulses Research Articles

Simultaneous Trapping of Two Optical Pulses in an Atomic Ensemble as Stationary Light Pulses.

The stationary light pulse (SLP) refers to a zero-group-velocity optical pulse in an atomic ensemble prepared by two counterpropagating driving fields. Despite the uniqueness of an optical pulse trapped within an atomic medium without a cavity, observations of SLP so far have been limited to trapping a single optical pulse due to the stringent SLP phase-matching condition, and this has severely hindered the development of SLP-based applications. In this Letter, we first show theoretically that the SLP process in fact supports two phase-matching conditions and we then utilize the result to experimentally demonstrate simultaneous SLP trapping of two optical pulses for the duration from 0.8 to 2.0 μs. The characteristic dissipation time, obtained by the release efficiency measurement from the SLP trapping state, is 1.22 μs, which corresponds to an effective Q factor of 2.9×10^{9}. Our Letter is expected to bring forth interesting SLP-based applications, such as, efficient photon-photon interaction, spatially multimode coherent quantum memory, creation of exotic photonic gas states, etc.

Trapping a free-propagating single-photon into an atomic ensemble as a quantum stationary light pulse

Efficient photon–photon interaction is one of the key elements for realizing quantum information processing. The interaction, however, must often be mediated through an atomic medium due to the bosonic nature of photons, and the interaction time, which is critically linked to the efficiency, depends on the properties of the atom–photon interaction. While the electromagnetically induced transparency effect does offer the possibility of photonic quantum memory, it does not enhance the interaction time as it fully maps the photonic state to an atomic state. The stationary light pulse (SLP) effect, on the contrary, traps the photonic state inside an atomic medium with zero group velocity, opening up the possibility of enhanced interaction time. In this work, we report the first experimental demonstration of trapping a free-propagating single-photon into a cold atomic ensemble via the quantum SLP (QSLP) process. We conclusively show that the quantum properties of the single-photon state are preserved well during the QSLP process. Our work paves the way for new approaches for efficient photon–photon interactions, exotic photonic states, and many-body simulations in photonic systems.

Numerical study of large cross-phase modulation with stationary light pulses

We report a systematic investigation of cross-phase modulation using techniques of light storage (LS) and stationary light pulse (SLP) based on the effect of electromagnetically induced transparency. Two light fields are stopped in the medium to prolong the interaction time, which enhances the efficiency of optical nonlinearity. We numerically study the properties of the signal SLP field such as lifetime, light pulse storage efficiency, and stored peak intensity as functions of optical density (OD) and coupling field intensity. The strong nonlinearity between LS and SLP photons leads to a phase shift of up to π at the single-photon level. Meanwhile, both the LS and SLP photons maintain energy transmission higher than 20%, as the OD of the SLP subsystem is larger than 700. The energy transmission and phase shift can be further improved by increasing the OD of the medium. The performance of the quantum phase gate between two single photons is expected by applying such strong photon interaction.

Efficient polarization beam splitter based on the optimized stationary light pulse

A tripod-double M type atomic system is proposed for generating stationary light pulse (SLP) encoded in degree of freedom of polarization, and realizing configurable polarization beam splitter through the active operation of the controlling fields and the additional intensity-modulated weak microwave fields. Compared to the previous work [Phys. Rev. A, 100 (2019) 013844], the present one has the following advantages: (1) the generated SLP and the retrieved signal field can be amplified or decreased in a controllable manner, (2) beam-splitting ratio of the left and the right circularly polarized components can be flexibly and continuously configurable in a wide range, and (3) the frequency and the polarization state of the input signal field can be converted. The current scheme, integrating multiple functions and showing excellent performance, may find promising applications in all-optical information processing.

Efficient generation of stationary light pulses due to coupling between two lower levels

A double- $$\varLambda $$ system, the two low levels of which is connected by an additional weak intensity-modulated microwave field as the controlling fields are switched off, is exploited for efficient generation of stationary light pulse (SLP). Analytical and numerical results show that due to the constructive or destructive interference between the introduced microwave field and the atomic spin coherence, the generated SLP and the retrieved signal field can be optimized or degenerated without causing distortion through modulating the intensity and phase of the microwave field.

Efficient all-optical router and beam splitter for light with orbital angular momentum.

We propose an efficient scheme for realizing all-optical router or beam splitter (BS) by employing a double tripod-type atomic system, where the ground levels are coupled by two additional intensity-dependent weak microwave fields. We show that the high-dimensional probe field encoded in a degree of freedom of orbital angular momentum can be stored, retrieved, and manipulated. Due to the constructive or destructive interference between the introduced microwave fields and the atomic spin coherence, the generated stationary light pulses and the retrieved probe fields can be increased or decreased with high efficiency and fidelity in a controllable manner. On the basis of the results and a general extension, a tunable all-optical router or BS, which can split a high-dimensional probe field into two or more ones, can be achieved by actively operating the controlling fields and the microwave fields. The current scheme, integrating multiple functions and showing excellent performance, could greatly enhance the tunability and capacity for the all-optical information processing.

Single-photon-level narrowband memory in a hollow-core photonic bandgap fiber

An experimental platform operating at the level of individual quanta and providing strong light-matter coupling is a key requirement for quantum information processing. In our work, we show that hollow-core photonic bandgap fibers filled with laser-cooled atoms might serve as such a platform, despite their typical complicated birefringence properties. To this end, we present a detailed theoretical and experimental study to identify a fiber with suitable properties to achieve operation at the single-photon level. In the fiber, we demonstrate the storage and on-demand retrieval as well as the creation of stationary light pulses, based on electromagnetically induced transparency, for weak coherent light pulses down to the single-photon level with an unconditional noise floor of 0.017(4) photons per pulse. These results clearly demonstrate the prospects of such a fiber-based platform for applications in quantum information networks.

Reversible storage and manipulation of light pulses with orbital angular momentum

We propose a scheme to realize the storage and retrieval of high-dimensional signal field with orbital angular momentum (OAM) in a double-$$\Lambda $$ system of cold atoms. By employing two counter-propagating controlling fields, we show that the system exists two shape-preserving dark-state polaritons, which propagate in the opposite direction. We demonstrate that stationary light pulses with OAMs can be generated when both the controlling fields are switched on for retrieving the stored signal field from the atomic spin coherence, and the signal fields with OAMs can be manipulated coherently and all-optically through the active operation of the controlling fields in direction and time. The proposed scheme can easily be extended to the reversible storage and manipulation of multiple signal fields with OAMs. Our work is promising for practical application of information processing with large capacity.

Coherent generation and manipulation of stationary light pulses encoded in degrees of freedom of polarization and orbital angular momentum

We propose a double-$\mathsf{M}$ system of cold atoms for realizing the reversible storage and manipulation of signal fields encoded in degrees of freedom (DOFs) of polarization and orbital angular momentum (OAM). By employing two pairs of counterpropagating controlling fields, we show that the system exhibits dark state polaritons relating to the polarization and propagation direction of the light fields. Through the active operation of the controlling fields in time, stationary light pulses with polarizations and OAM information can be generated due to the tight coupling and balanced competition between the retrieved signal fields, and can be manipulated coherently and all-optically. Another advantage of our proposed scheme is that the two polarization components of the signal field can be decoupled and thus be independently retrieved from the atomic ensemble, and then the scheme can be employed to realize polarization-dependent beam splitting. Such a multiple DOF-dependent scheme could pave the way toward quantum nonlinear optics without a cavity, and could greatly enhance the tunability and capacity for both classical and quantum information processing.

Formation of a Stationary Light Pulse in a Doppler-Broadened EIT Medium

A number of experiments have been performed on light slowing and stopping in the electromagnetically induced transparency (EIT) media of hot atomic gases where the Doppler-shift may add detunings to the field frequencies in an inhomogeneous fashion. We provide here a theoretical analysis as to the effect of such a Doppler-broadened environment on the dynamics of the system in comparison to a cold atomic medium. We will show that one of the most critical factors in the formation of a stationary light pulse is the enhancement of the excited-state decay rate caused by the collisions between the atoms of the medium and the molecules of the buffer gas.

Experimental Demonstration of Quantum Stationary Light Pulses in an Atomic Ensemble

A new experiment demonstrates a quantum stationary light pulse---a nonclassical approach to stopping light---in a cold atomic ensemble, which could pave the way toward novel quantum materials, optics, and devices.

Dynamic generation and coherent control of beating stationary light pulses by a microwave coupling field in five-level cold atoms

We propose an efficient scheme for generating and controlling beating stationary light pulses in a five-level atomic sample driven into electromagnetically induced transparency condition. This scheme relies on an asymmetrical procedure of light storage and retrieval tuned by two counter-propagating control fields where an additional coupling field, such as the microwave field, is introduced in the retrieval stage. A quantum probe field, incident upon such an atomic sample, is first transformed into spin coherence excitation of the atoms and then retrieved as beating stationary light pulses exhibiting a series of maxima and minima in intensity due to the alternative constructive and destructive interference. It is convenient to control the beating stationary light pulses just by manipulating the intensity and detuning of the additional microwave field. This interesting phenomenon involves in fact the coherent manipulation of dark-state polaritons and could be explored to achieve the efficient temporal splitting of stationary light pulses and accurate measurement of the microwave intensity.

Light Trapping above the Light Cone in One-Dimensional Arrays of Dielectric Spheres

We demonstrate bound states in the radiation continuum (BSC) in a linear periodic array of dielectric spheres in air above the light cone. We classify the BSCs by orbital angular momentum m = 0,±1,±2 according to the rotational symmetry of the array, Bloch wave vector ꞵ directed along the array according to the translational symmetry, and polarization. The most simple symmetry protectedBSCshavem = 0,ꞵ = 0 and occur in a wide range of the radius of the spheres and dielectric constant. More sophisticated BSCs with m 6= 0,ꞵ = 0 exist only for a selected radius of spheres at fixed dielectric constant. We also find robust Bloch BSCs with ꞵ 6= 0,m = 0. All BSCs reside within the first but below the other diffraction continua. We show that the BSCs can be easily detected by bright features in scattering of different plane waves by the array as dependent on type of the BSC. The symmetry protected TE/TMBSCs can be traced by collapsing Fano resonance in cross-sections of normally incident TE/TM plane waves. When plane wave with circular polarization with frequency tuned to the bound states with OAM illuminates the array the spin angular momentum of the incident wave transfers into the orbital angular momentum of the BSC.This ,inturn, gives rise to giant vortical power currents rotating around the array. Incident wave with linear polarization with frequency tuned to the Bloch bound state in the continuum induces giant laminar power currents. At last, the plane wave with linear polarization incident under tilt relative to the axis of array excites Poynting currents spiralling around the array. It is demonstrated numerically that quasi-bound leaky modes of the array can propagate both stationary waves and light pulses to a distance of 60 wavelengths at the frequencies close to the bound states in the radiation continuum. A semi-analytical estimate for decay rates of the guided waves is found to match the numerical data to a good accuracy.

Stationary light pulses and narrowband light storage in a laser-cooled ensemble loaded into a hollow-core fiber

We report on the first observation of stationary light pulses and narrowband light storage inside a hollow-core photonic crystal fiber. Laser-cooled atoms were first loaded into the fiber core providing strong light-matter coupling. Light pulses were then stored in a collective atomic excitation using a single control laser beam. By applying a second counterpropagating control beam, a light pulse could be brought to a standstill. Our work paves the way towards the creation of strongly-correlated many-body systems with photons and applications in the field of quantum information processing.

Light guiding above the light line in arrays of dielectric nanospheres.

We consider light propagation above the light line in arrays of spherical dielectric nanoparticles. It is demonstrated numerically that quasi-bound leaky modes of the array can propagate both stationary waves and light pulses to a distance of 60 wavelengths at the frequencies close to the bound states in the radiation continuum. A semi-analytical estimate for decay rates of the guided waves is found to match the numerical data to a good accuracy.

On the retrieval efficiency of light storage in an EIT medium

We investigate the retrieval efficiency of light slowed and/or stored in a medium with electromagnetically-induced transparency (an EIT medium) by numerical simulations based on first principles. Starting from the master equation formulation, we derive the full dynamics of the system and then show how the approximations are applied to reduce the number of dynamical equations. While operating the system as an optical “retarder,” a “reflector,” and a “beam-splitter,” we find that the total retrieval efficiency in the case of the “beam-splitter” operation is lower than that in either of the other two operations. Nevertheless, we find that (1) when an appropriate value of detuning is applied between the two counter-propagating “read”-fields, the retrieval efficiency in the latter case can be significantly improved, (2) storing the signal in the form of the atomic spin wave is more advantageous than storing it in the form of a stationary light pulse (SLP), and (3) the retrieval efficiency can be augmented by increasing the strengths of the “read”-fields.

A Numerical Analysis of a Light Slowing and Storage

We provide an in-depth numerical study on creation of stationary light pulses (SLP) in a cold atomic medium, locating the optimal parameter space for experimental realization. We visualize the dynamics of the atoms and the field inside the medium. We find that as the coupling field strength increases, the light slowing effect is actually diminished. It also turns out that the spatial profile of the pulse inside the medium is indeed not symmetric around its apex, and we point out that this asymmetry causes the energy imbalance between the two signals retrieved into the opposite directions, in addition to such extrinsic reasons as the disparity between the coupling field strengths or the imperfect centering of the pulse in the medium at the time of “writing”.

Phase control of stationary light pulses due to a weak microwave coupling

We study the dynamic control of stationary light pulses generated in a sample of cold atoms driven into the double-Λ configuration with two ground levels coupled by a weak microwave field. This microwave field can modify the spin coherence of two ground levels through its phase and amplitude, and then increase or decrease the intensity of a stationary light pulse generated from this spin coherence. Such phase-modulation technique is essential to maximize the effective interaction time between light and matter in photonic information processing and therefore facilitate the achievement of enhanced optical nonlinearities at low-light levels.

Stationary and quasistationary light pulses in three-level cold atomic systems

We have studied stationary and quasistationary signal light pulses in cold \ensuremath{\Lambda}-type atomic media driven by counterpropagating control laser fields at the condition of electromagnetically induced transparency. By deriving a dispersion relation we present spectral and temporal properties of the signal light pulse and a significant influence of atomic decoherence on the coupled stationary light pulses for spatial splitting. Finally we discuss quasistationary light pulse evolution characterized by frozen spatial spreading for a robust coherent control of slow light pulses.

Coherent generation and efficient manipulation of dual-channel robust stationary light pulses in ultracold atoms

We study the dynamic processes of reversible dual-channel light memory in a double-tripod atomic system by modulating only a pair of counterpropagating control fields in time. We find that two pairs of stationary light pulses (SLPs) can be simultaneously generated when we switch on both control fields after storage. Two incident signal fields in two channels can be released either simultaneously from the same surface of the sample, or at different times from the same or different surfaces of the sample, depending on the time modulation of the two control fields, the time sequence of the input signal fields, and the group velocities of the signal fields propagating in medium, which could be successfully manipulated in each channel. Comparing with the light storage in spin-wave excitations, the SLPs may suffer a little space-dependent diffusion but maintain optical components required for nonlinear optical interactions. These results could be used to study the enhanced low-noises nonlinear interaction between dual-channel SLPs, which can maximize the interaction time. Besides, this scheme could also be explored to design synchronous multitasking information processing during light memory processes at low-light even below single-photon level.