Λ-type System Research Articles

Time-bin entanglement in the deterministic generation of linear photonic cluster states

We theoretically investigate strategies for the deterministic creation of trains of time-bin entangled photons using an individual quantum emitter described by a Λ-type electronic system. We explicitly demonstrate the theoretical generation of linear cluster states with substantial numbers of entangled photonic qubits in full microscopic numerical simulations. The underlying scheme is based on the manipulation of ground state coherences through precise optical driving. One important finding is that the most easily accessible quality metrics, the achievable rotation fidelities, fall short in assessing the actual quantum correlations of the emitted photons in the face of losses. To address this, we explicitly calculate stabilizer generator expectation values as a superior gauge for the quantum properties of the generated many-photon state. With widespread applicability in other emitter and excitation–emission schemes also, our work lays the conceptual foundations for an in-depth practical analysis of time-bin entanglement based on full numerical simulations with predictive capabilities for realistic systems and setups, including losses and imperfections. The specific results shown in the present work illustrate that with controlled minimization of losses and realistic system parameters for quantum-dot type systems, useful linear cluster states of significant lengths can be generated in the calculations, discussing the possibility of scalability for quantum information processing endeavors.

Electromagnetically induced transparency with magnetically induced ΔF=0,mF=0→mF=0 probe transition

Interest in magnetically induced (MI) transitions of alkali metal atoms is caused by the fact that their intensities can exceed the intensities of ‘regular’ atomic transitions in a wide magnetic field range (200–4000 G). The goal of this work was to form and study, for the first time, electromagnetically induced transparency (EIT) resonance in a strong magnetic field using probe radiation tuned to |Fg=F,mF=0⟩→|Fe=F,mF=0⟩ MI transition, which is forbidden in zero magnetic fields. Two narrow-band linearly polarized cw diode lasers were used to form EIT resonance on a Λ-type system of a Cs atomic D2 line in a strong transverse magnetic field (up to 1000 G). The resonance was formed in a Cs atomic vapor nanocell with an atomic vapor column thickness of 850 nm.

Velocity selective multiple two-photon dark and bright resonances in Potassium vapor

We report the observation of two additional sub-natural line width quantum interferences in the D 2 manifold of 39 K vapor, in addition to the usual single Electromagnetically Induced Transparency (EIT) peak. In a typical three level Λ-type system, only one EIT peak is observed. However, here we report observation of two additional line shapes riding on top of the absorption profile. The fact that the hyperfine splitting is smaller than the Doppler width in 39 K allows the probe and control beams to swap their transition pathways in different velocity groups of atoms even when their frequencies are kept constant. Our observations are in striking contrast to standard EIT measurements. These findings are in quantitative agreement with density matrix formalism taking into account velocity-selective two-photon resonances. Owing to the favorably low ground hyperfine splitting (Δ hf ) in 39 K, which allows a significantly large number of atoms with a Doppler shift greater than or equal to the Δ hf , the strength of these additional resonances is strong compared to that of other alkali atoms such as 87 Rb, 133 Cs where these resonances can not be observed. The control photon detuning to atomic transition captures the nature of the coherence; therefore an unusual phenomenon of conversion from perfect transparency to enhanced absorption of the probe photon is observed and explained by utilizing the adiabatic elimination of the excited state in the Master equation. Controlling such dark and bright resonances leads to new applications in quantum technologies such as frequency-offset laser stabilization and long-lived quantum memory.

Optical storage of circular airy beam in atomic vapor

Abstract The realization of quantum storage of spatial light field is of great significance to the construction of high-dimensional quantum repeater. In this paper, we experimentally realize the storage and retrieval of circular Airy beams (CABs) by using the Λ-type three-level energy system based on the electromagnetically induced transparency in a hot rubidium atomic vapor cell. The weak probe beam field is modulated with phase distribution of CABs by a spatial light modulator. We store the probe circular Airy beam (CAB) into the rubidium atomic vapor cell and retrieve it after the demanded delay. We quantitatively analyze the storage results and give corresponding theoretical explanations. Moreover, we investigate the autofocusing and self-healing effect of the retrieved CAB, which indicates that the properties and beam shape of CAB maintain well after storage. Our work will have potential applications in the storage of high-dimensional quantum information, and is also useful for improving the channel capacities of quantum internet.

Magnetic splitting of electromagnetically induced transparency and absorption spectra in a standing-wave coupled lambda-type system

We study the splitting of traveling wave and standing wave coupled Electromagnetically Induced Transparency (EIT) and Electromagnetically Induced enhanced Absorption (EIA) lines in the presence of a uniform magnetic field in an Electromagnetically Induced Grating (EIG). We realize a Λ-type system in a room-temperature Doppler-broadened buffer-gas-free, unshielded vapor cell of pure 133Cs atoms. Different orientations of the magnetic field are studied while the polarizations of the coupling and probe laser beams are arranged in the lin⊥lin configuration. The effects of the different field directions on the EIT and the EIG-induced EIA are explained in light of the existing theory. The magnetically induced high-contrast features in the EIG scheme are also discussed in comparison to the low-contrast EIT features observed for the same strengths of magnetic field.

Gain-assisted quantum heat engine based on electromagnetically induced transparency

We propose a scheme to realize a gain-assisted quantum heat engine (QHE) based on electromagnetically induced transparency (EIT), which consists of a three-level Λ-type atomic system interacting with two thermal reservoirs and a coupling field. The gain without inversion is induced to the system via spontaneously generated coherence (SGC) between two lower levels. The SGC has significantly affect on the system’s dynamics, resulting in an enhancement of the emission cross-section and spectral brightness of the QHE.

Proposal for composite quantum electromagnetically induced transparency heat engine coupled by a nanomechanical mirror

Abstract This paper introduces a quantum heat engine model that utilizes an ultracold atomic gas coupled with a nanomechanical mirror. The mirror’s vibration induces an opto-mechanical sideband in the control field, affecting the behavior of the cold gas and subsequently influencing the output radiation of the engine. The model incorporates mirror vibration while omitting cavity confinement, establishing a bridge between a multi-level atom–laser interacting system that plays with coherences and the mechanical vibration of the nanomechanical mirror, which jointly function as heat engines. Three distinct heat engine configurations are proposed: the first involves a vibration-free three-level Λ-type system, the second introduces nanomechanical vibration to the three-level Λ-type system, and the third constitutes a composite engine that combines the previous setups along with nanomechanical vibration. The spectral brightness of a three-level heat engine is diminished with mirror vibration, whereas for a composite heat engine, there is a slight enhancement in the brightness peak. However, the maximum brightness is attained when there is no vibration. Comparisons between the proposed model and an ideal system are made regarding entropy balance, adhering to the constraints of the second law of thermodynamics. The model observed that when subjected to mirror vibration, the proposed heat engines diverged from the characteristics expected in an ideal heat engine.

Dynamic all-optical memory switching based on atomic optical bistable behavior in a three level Λ-type atomic system

We theoretically investigate the atomic optical bistability (AOB) in a three-level Λ-type atomic system confined in a unidirectional optical ring cavity. The role of the intensity or detuning of the control field on AOB is explored, and results show that absorption, dispersion, and nonlinearity can be modified significantly by the control field due to quantum coherence and interference in multilevel atomic systems. Thus, tuning the intensity or detuning of the control field can manipulate the switch-up and switch-down thresholds, as well as the area of the bistable hysteresis loop. According to the controllability of AOB, we design various schemes to realize dynamical all-optical switching between the high and low outputs of two bistable curves for a fixed cavity input. In addition, dynamical all-optical memory switching can be implemented by adding a pulse sequence for the intensity or detuning of the control field. For appropriate parameters, such as the cooperative coefficient, the extinction ratio of the switching can be improved dramatically.

Highly efficient creation and detection of deeply bound molecules via invariant-based inverse engineering with feasible modified drivings.

Stimulated Raman Adiabatic Passage (STIRAP) and its variants, such as M-type chainwise-STIRAP, allow for efficiently transferring the populations in a multilevel system and have widely been used to prepare molecules in their rovibrational ground state. However, their transfer efficiencies are generally imperfect. The main obstacle is the presence of losses and the requirement to make the dynamics adiabatic. To this end, in the present paper, a new theoretical method is proposed for the efficient and robust creation and detection of deeply bound molecules in three-level Λ-type and five-level M-type systems via "Invariant-based shortcut-to-adiabaticity." In the regime of large detunings, we first reduce the dynamics of three- and five-level molecular systems to those of effective two- and three-level counterparts. By doing so, the major molecular losses from the excited states can be well suppressed. Consequently, the effective two-level counterpart can be directly compatible with two different "Invariant-based Inverse Engineering" protocols; the results show that both protocols give a comparable performance and have a good experimental feasibility. For the effective three-level counterpart, by considering a relation among the four incident pulses, we show that this model can be further generalized to an effective Λ-type one with the simplest resonant coupling. This generalized model permits us to borrow the "Invariant-based Inverse Engineering" protocol from a standard three-level Λ-type system to a five-level M-type system. Numerical calculations show that the weakly bound molecules can be efficiently transferred to their deeply bound states without strong laser pulses, and the stability against parameter variations is well preserved. Finally, the detection of ultracold deeply bound molecules is discussed.

Discrete dynamics of light in an anti-parity-time symmetric photonic lattice in atomic vapors.

We demonstrate the realization of an anti-parity-time (PT)-symmetric photonic lattice in a coherent three-level Λ-type 85Rb atomic system both experimentally and theoretically. Such an instantaneously reconfigurable anti-PT-symmetric photonic lattice is "written" by two one-dimensional coupling fields, which are arranged alternately along the x direction and can modulate the refractive index of the atomic vapor in a spatially periodical manner via controllable atomic coherence. By properly adjusting the relevant atomic parameters, the phase shift between two adjacent lattice channels occurs in the constructed non-Hermitian photonic system. Such a readily reconfigurable anti-PT-symmetric photonic lattice may open the door for demonstrating the discrete characteristics of the optical waves in periodic anti-PT-symmetric photonic systems.

Conical diffraction in atomic vapor: Mathematical models and numerical calculations

This study investigated the conical diffraction characteristics in the honeycomb lattice of a Λ-type three-level energy system for rubidium atomic configuration. Its band structure incorporates Dirac cones in accordance with the plane wave expansion method. We determined that the rotation angle θ of the three vectors strongly impacted the cone diffraction profile. For θ=0° and 60°, in the reciprocal lattice space, the Dirac cone states were excited, and symmetric cone diffraction was supported. When 0<θ<60°, an asymmetric cone diffraction with a dark notch appeared on the outer edge of the conical ring. The results indicate that the frequency detuning of the coupling field and high-order nonlinear susceptibilities in the medium are effective and concise approaches to manipulate the occurrence of cone diffraction. The findings of this study enhance the understanding of the cone diffraction phenomena and broaden the practical applicability of atomic configuration.

Quantum state engineering in a three-level system with periodical Gaussian pulses

In this paper, we propose a scheme to achieve selective population transfer in a Λ-type three-level atomic system with a train of periodical Gaussian pulses. Based on temporal constructive quantum interference between the sequential transitions and subsequent coherent accumulations, the selective population transfer can be achieved with the pulse train, without satisfying the requirement of two-photon resonance condition. It can be understood as a result of the formation of a comb-like structure of the pulse train spectrum in time domain. Numerical simulations demonstrate that the scheme is robust against the wave-form deformation of single pulse while sensitive to the pulse train repetition period. Due to the Gaussian waveform of the laser field been readily implemented in experiments, the scheme holds great practicality for quantum state engineering in quantum information processing.

Tunable atom lithography scheme with high resolution in atomic system

We theoretically propose a scheme that utilizes the excited state of a Λ-type three-level atom system for atom lithography. A standing-wave coupling field and a probe field provide localized probability distribution of the excited atoms. Unlike the previous studies in atom localization, we focus on splitting the single-peak structure localized on the node of the standing-wave field to a double-peak structure. The shift distance of double-peak related to the parameters of external laser fields is investigated. The period of lithography pattern could reach λ/4, while the resolution of lithography is promising to be smaller than 0.02λ by adjusting system parameters. This scheme can be extended to form a two-dimensional pattern for lithography.

Generation and Controllability of High-Dimensional Rogue Waves in an Electromagnetically Induced Transparent Medium

We propose a scheme to generate and control high-dimensional rogue waves in a coherent three-level Λ-type atomic system via electromagnetically induced transparency (EIT). Under EIT conditions, the probe field envelopes obey the non-integrable nonlinear Schrödinger equations (NLSE) with or without the external potential, which result from the stark (Zeeman) effect contributed by an electric (magnetic) field. By adjusting the amplitude and width of the initial pulse, we can generate the high-dimensional rogue waves and obtain the phase-transition curves of high-dimensional rogue waves. In the system, the far-detuned electric field, the random weak magnetic field, and the Gauss weak magnetic field are not conducive to the excitation of high-dimensional rogue waves. The results not only provide a theoretical basis for the experimental realization or prevention of the high-dimensional rogue waves, but also prove the possibility of generating and controlling the rogue waves in other high-dimensional non-integrable systems.

Transient fluorescence with a single trapped ion

In this paper, we present a method to measure transient fluorescent dynamics with single trapped ions in a Paul trap. We use 40Ca+ ions that exhibit a Λ-type three-level system and measure the characteristic optical pumping times between the ground S1/2 and the meta-stable D3/2 levels. We prepare one of these states and then pump it to the opposite via the excited P1/2 state. By measuring the scattered photons of the ion, we retrieve transient curves of the atomic fluorescence. These curves provide fundamental information about the atomic system, such as branching fractions and excited-state lifetimes, as well as experimental parameters like the efficiency of the detection system and the saturation parameter of one of the transitions. Finally, we study the time-dependent fluorescence as a function of optical power and detuning of the lasers and find a very good agreement with simulating the dynamics via a three-level open quantum system through a set of optical Bloch equations. Being able to record time-dependent fluorescence is of particular interest as it contains information about the temperature, cooling, and heating dynamics of the ion.

Polarization-insensitive electromagnetically induced transparency-like and dual-band absorption based on graphene and vanadium dioxide metamaterials

In this work, a dynamically tunable and polarization-insensitive electromagnetically induced transparency-like (EIT-like) and dual-band absorption based on graphene and vanadium dioxide metamaterial is proposed. The unit cell of the metamaterial consists of two monolayer graphene square rings of different sizes. The transparent window results from the near-field coupling can be observed in the x and y polarization directions, respectively. The EIT-like effect can be tuned by changing the Fermi energy of graphene. The three-level Λ-type system and the distribution of the electric field on |Ez| are employed to explain the physical mechanism of the EIT-like effect clearly. The theoretical fitting results based on the coupled oscillator model are in good agreement with the numerical simulation results. In addition, by introducing vanadium dioxide (VO2) and utilizing the phase change property of VO2, the designed metamaterial can realize the transition from an analog of electromagnetically induced transparency to a dual-band absorber which has two absorption bands in the frequency range of 0.2–3 THz and the absorption rate reaches 63.2% at 0.96 THz and 99.6% at 1.89 THz. Furthermore, we investigate the performance of metamaterials to probe the refractive index of the surrounding medium and our prototype exhibits a highest sensitivity value of about 0.4845 THz/RIU. This proposed design provides a viable approach for developing slow-light devices, sensors, absorption, and multifunctional devices.

Stimulated Raman adiabatic passage with trains of weak pulses* *This work is dedicated to Bruce Shore, a brilliant and inspiring physicist, a pioneer in coherent light–matter interaction theory, a mentor and a friend.

We consider coherent population transfer in multilevel quantum systems driven by time-delayed pulse trains. We show how to choose the parameters of the trains so that the population dynamics tracks the behavior of a Λ-type three-level system under stimulated Raman adiabatic passage (STIRAP). Efficient population transfer can be achieved regardless of the order and with or without overlap of the pump and the Stokes sub-pulses of the trains. Generalized STIRAP schemes of population transfer in N-level system with sequential couplings are also examined. The mechanism of the population transfer and the robustness of the proposed schemes are discussed.

Phase control of all-optical switching based on spontaneously generated coherence in a three-level Λ-type atomic system

Phase control of all-optical switching based on spontaneously generated coherence in a three-level Λ-type atomic system

Optical effects of quantum systems coupled with one- and two-dimensional structured baths

We study the probe absorption and dispersion properties of a Λ-type quantum system which is coupled to one- and two-dimensional bosonic structured reservoirs. Using as structured reservoirs the one-dimensional model with nearest-neighbor coupling, as well as, a two-dimensional bath with square-lattice symmetry, we show the modification to the optical properties of the Λ-type system and present the conditions for which the system may become transparent to a probe field. Due to the unique band structures emerge from the bath periodicity, transparency presents interesting behavior in the strong coupling regime. The potential for all-optical photon switching is also presented. The effects presented here could be useful in quantum technologies for the creation of all-optical quantum logic gates and switches.

Stimulated Raman adiabatic passage in a quantum system near a plasmonic nanoparticle

We investigate theoretically the population transfer process in a Λ-type three-level quantum system (QS) near a metallic nanosphere using the stimulated Raman adiabatic passage (STIRAP) technique. We combine density matrix quantum dynamical calculations with first-principle electromagnetic calculations, which quantify the influence of the plasmonic nanoparticle on the electric field of the pump and Stokes pulses in STIRAP as well as on the spontaneous emission rates within the Λ-type system. We study the population transfer process by varying the free-space spontaneous emission rate, the distance of the QS from the nanosphere, the polarization direction with respect to the nanoparticle surface and the relative strength of the pump and Stokes pulses used in STIRAP. We find that when the pump and Stokes fields have tangential and radial polarizations with respect to the nanosphere surface, the transfer efficiency is improved due to the increase of the decay rate of the excited state to the target state relatively to the decay to the initial state. The optimal population transfer is achieved for small interparticle distances, moderate free space spontaneous decay rate, large values of the pump Rabi frequency and small values of the Stokes Rabi frequency. When we exchange the polarization directions of the pump and Stokes fields we can still find a range of parameters where the population transfer remains efficient, but larger Stokes Rabi frequencies are necessary to overcome the increased decay rate from the excited state back to the initial state.