Atomic Coherence Research Articles

Two-channel cross-phase modulation based on the reversible storage of light in a cold atomic system

We propose a five-level quasi-tripod type atomic system for realizing two-channel cross-phase modulation (XPM) based on the light-storage. Due to the existence of the double dark-state polaritons, both probe fields can be coherently mapped into and out of the cold atoms by switching off and on the coupling field adiabatically. The analytic results and the numerical simulations show that the application of an additional weak microwave field during the storage time can efficiently modify the atomic spin coherence, and a continuous and controllable phase shift can be imposed on the retrieved probe fields with negligible attenuation in the amplitude. The phase shift and the energy retrieving rate of the probe fields are neither influenced by the coupling field nor by the atomic optical density. Such a novel scheme can be easily extended to realize the XPM of multiple-probe fields and may find potential applications in multiple-channel classical and quantum information processing.

Generation of quintupartite entanglement with an atom-assisted dual-cavity optomechanical system

We present a proposal to generate quintupartite entanglement with an optomechanical dual-cavity containing an ensemble of Λ-type three-level atoms. By solving the Heisenberg-Langevin equations, we show that entanglement among the two cavity fields, two mechanical oscillators, and atoms can be realized via atomic coherence and cavity field radiation pressure. In addition, within the experimentally available range of parameters, the larger the input laser power, atomic ensemble number, and quality factors of the cavity and mechanical oscillators, and the smaller the environmental temperature, the stronger the multipartite entanglement. This atom-cavity-optomechanical hybrid system provides an efficient and convenient platform for quantum states exchange between macroscopic (mechanical oscillators) and microscopic (atoms, photons) matters, and may find promising applications in realistic quantum information processing.

Laser interferometry based on atomic coherence

We demonstrate laser interferometry based on phase difference between the two arms of an interferometer. The experiments are done with a Cs atomic vapor cell at room temperature and use atomic coherence. The interference can be tuned from constructive to destructive by tuning the relative phase between the two arms. It is similar to the Michelson interferometer, but differs in the important aspect of allowing interference when the polarizations in the two arms are orthogonal. This would be a novel method for interfering two independent lasers, which can even allow interfering two independent lasers of completely different wavelengths.

Atomic population inversion and absorption dispersion-spectra driven by modified double-exponential quotient pulses in a three-level atom

In this study, we control a three-level atomic system using a typical strong control field with a modified quotient double exponential form (modified QEXP). The considered atomic configuration is a V-type three-level system in which QEXP is applied between the ground and excited states. Atomic population inversion can be achieved by selecting specific shaped pulses. In addition, we control the temporal atomic coherence of the system for a spectrum of waveforms and derive both absorption and dispersion spectra. Compared to a continuous wave control field, the proposed modified QEXP pulse achieves an electromagnetically induced transparency window in the absorption spectrum.

Study of the optical response and coherence of a quadratically coupled optomechanical system

In this article, we theoretically investigate a quadratically coupled optomechanical system with a two-level atom. At steady-state, we examine the variation of transmission intensity with various parameters of the system as well as investigate the transmission in lower/upper sidebands. Moreover, taking into account the quantum fluctuations, we extend our investigation towards the study of quantum coherence for the optomechanical system. The result shows that the coherence inside the proposed cavity can be efficiently controlled by varying atom-to-photon coupling and modified optical detuning. We also discuss and provide a physical explanation of why the atomic coherence can surpass the optical and mechanical ones.

The different behaviors of thermal noise in collective quantum steering and genuinely tripartite steering induced by atomic coherence

Multipartite quantum steering has important application in quantum information processing. Here we study the influence of thermal noise on the collective quantum steering and genuine tripartite steering in a system of four-level inverted Y-type atoms, in which the atomic coherence is initially prepared and the cavity is coupled to a thermal reservoir. It is found that for the cases of the balanced and unbalanced cavity losses, the thermal noise plays a positive role in realizing the collective steering. However the case is different for the genuine tripartite steering effect. For the case of either balanced or unbalanced cavity losses, the thermal noise would destroy genuine tripartite steering effect and reduce the parameter region of genuine tripartite steering. The thermal noise plays a negative role in realizing genuine tripartite steering. Specially, it is verified that the genuine tripartite steering does not reject the bipartite steering, which is very different from the collective quantum steering requiring no bipartite steering. The present scheme may provide some help for potential applications such as quantum communication.

Rydberg atom based microwave sensing and communication

With the overall redefinition of the international system of units (SI), the classical physical standards are gradually replaced by the natural standards based on quantum physics. Due to the reproducibility, accuracy and stability of atomic system, many new technologies of quantum precision measurement have been developed based on the atomic systems. Rydberg atoms are very sensitive to external electromagnetic fields because of their large MW transition dipole moment and polarizability. With the atomic coherence effect, the ultra wideband electric field can be measured with high precision and high sensitivity. Especially for the microwave range whose frequency is higher than 1 GHz, the research of establishing microwave quantum standard is advancing steadily. In addition, all optical materials and ultra wide band atomic antenna have a wide range of applications in aerospace, military communications and other fields. In this paper, we review the researches of microwave sensing and communication based on Rydberg atoms, and introduce the progress in the quantum standard of microwave electric field strength, coherent detection, radio-over-fiber, digital communication, etc., and discuss the possible applications and research frontiers in this rapid developing field.

Plasmon's Fizeau‐dragging effect at the interface of atomic and nano‐composites media

AbstractThe velocity uncertainty by Fizeaus plasmon dragging‐effect is investigated at the interface of four level atomic medium and Silver Silica (AgSiO2) nano‐composites material by using surface plasmon polaritons(SPPs) waves. We measured the real part of the dispersion relation Re(Ksp) = 1.5K0 with probe and control field detunings and Re(Ksp) = 1.36K0 with control field Rabi frequencies ∣Ω1,2 ∣ /γ. Furthermore, Re(Ksp/K0) = 1.8 with damping rate γ42/γ and volume frictional change fm. A large kink in the real part of dispersion relation of SPPs was measured in the large interaction region. The group index is in the range of ±20. The maximum dragging coefficient is ±20. The relative phase difference due to dragging is enhance by factor of −1.5 × 10−8rad. The propagation time is measured to be 0.8 ns with both control field Rabi frequencies. The volume fractional change of nano particles, probe/control field detuning and Rabi frequency of control field significantly influence the dragging coefficient, relative phase difference and velocity uncertainty. Including Fizeau‐Dragging effect in the given configuration the velocity uncertainty is measured to be 15 μm/s which is much larger than the velocity width of Kuan et al, used Δva = (8kBTln2/m)1/2 = 176 mm/s. The velocity uncertainty could be improved to 0.1 μm/s by taking large ensemble of atomic coherence and large delay/advance in time due to SPPs.

Microwave controlled ground state coherence in an atom-based optical amplifier

We experimentally investigate and theoretically analyze the effect of microwave controlled atomic ground state coherence on the phase-dependent amplification (PDA) of an optical probe field. We use three hyperfine levels in room temperature 85Rb atoms, which are cyclically connected by two optical and one microwave electromagnetic field. We show that a simultaneous fulfilment of a two-photon resonance condition that creates ground state coherence and a three-photon resonance condition leads to a significantly higher amplification of 7.5 dB of the optical probe field with a visibility of 98.8 %. By selectively breaking the ground state coherence using microwaves, we show that the amplification reduces with a bandwidth of 5 MHz. Nevertheless, the system shows non-zero PDA for large two-photon detunings of 15 MHz with high visibility of 66.8 %. This novel, controllable hybrid-PDA can be potentially used to trade-off amplification for bandwidth during the transmission of phase coherent classical and quantum information.

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.

Strongly-Entangled Twin Beams Produced by a Coherent Beat Laser Coupled to Thermal Reservoir

Applying the combination of the master and stochastic differential equations, we investigate in detail a continuous-variable entanglement of the twin beam generated by the coherent beat laser containing a parametric amplifier and coupled to thermal light of an external environment. The dipole-forbidden transition of the three-level atoms are coupled by the initial coherent superposition and classical pumping light emerging from the parametric oscillator. The atomic coherence induced by the classical pumping field and the initial coherent superposition induce a strong correlation between the two-mode radiation, which results in a high degree of the photon entanglement. In addition, the parametric amplifier enhances the achievable degree of entanglement of the two-mode fields. On the other hand, thermal light appears to degrade entanglement but a strong photon entanglement can be generated by managing the amount of thermal noise entering into the laser cavity through the output mirror.

Tunable quantum and statistical features of the two-mode radiation generated by a correlated emission laser injected with squeezed radiation

The role of phase fluctuation on the quantum and statistical features of the two-mode radiation produced by a correlated emission laser which is externally injected with squeezed radiation is discussed. The considered atoms are prepared in the ground and excited states with equal probabilities before being injected into the laser cavity, and an external coherent field generates the atomic coherence that leads to the non-classical features in the quantum system. A non-degenerate parametric amplifier is also introduced into the laser cavity which is coupled to a two-mode squeezed environment. It is found that the quantum and statistical properties are very sensitive to and highly altered by the phase fluctuation when the strength of the external coherent field is weak. On the contrary, the external coherent field entirely overcomes the influence of phase fluctuation for the amplitude of the external coherent field that lies in the strong pumping regime so that the strength of squeezing and entanglement, and photon statistics of the two-mode radiation are not substantially affected by the phase fluctuation.

Entanglement of atoms induced by thermal noise in the presence of initial atomic coherence

In this article, author investigated the dynamics of entanglement of two dipole-coupled natural or artificial two-level atoms (qubits) interacting nonresonantly with the intensive one-mode cavity thermal field. Author found an exact solution of the quantum Liouville equation for the full density matrix of the system two atoms + field mode for a coherent initial state of atoms in the dressed states representation. The full system density matrix is used to calculate the two-atom reduced density matrix and to calculate the quantitative criterion for atom-atom entanglement ‒ negativity. The results of computer simulation of the time dependence of negativity showed that in the case of a model with nonresonant interaction, the presence of initial atomic coherence leads to a significant decrease in the maximum degree of atomic entanglement, in contrast to the model with resonant interaction of atoms and a field. For the resonance model, the initial atomic coherence greatly enhances the degree of atomic entanglement.

Magnetic dipole interaction between a single-cycle microwave pulse and an atom

The manipulation of atoms by using a microwave (MW) field in precise atomic measurement and atomic chips is experiencing a renaissance. In this article, we study the magnetic dipole interaction (MDI) between a neutral 87 R b atom and a single-cycle MW field. Based on the strict analytic expression of the MW pulsed field radiated by the double L -type dipole transmitter, the MDI is simulated for different initial atom states and different detunings of the MW pulse. Our results show that the MDI can reach about one times the gravity of the atom, and it can change from a defocusing force to a focusing force on the coherent state atom depending on the distance from the emitter. Finally, the transient evolution of the coherent population transfer driven by the MW pulse is discussed. We hope that our calculation may help in understanding the coupling between an ultrashort MW field and an atom.

Half-minute-scale atomic coherence and high relative stability in a tweezer clock.

The preparation of large, low-entropy, highly coherent ensembles of identical quantum systems is fundamental for many studies in quantum metrology1, simulation2 and information3. However, the simultaneous realization of these properties remains a central challenge in quantum science across atomic and condensed-matter systems2,4-7. Here we leverage the favourable properties of tweezer-trapped alkaline-earth (strontium-88) atoms8-10, and introduce a hybrid approach to tailoring optical potentials that balances scalability, high-fidelity state preparation, site-resolved readout and preservation of atomic coherence. With this approach, we achieve trapping and optical-clock excited-state lifetimes exceeding 40 seconds in ensembles of approximately 150 atoms. This leads to half-minute-scale atomic coherence on an optical-clock transition, corresponding to quality factors well in excess of 1016. These coherence times and atom numbers reduce the effect of quantum projection noise to a level that is comparable with that ofleading atomic systems, which use optical lattices to interrogate many thousands of atoms in parallel11,12. The result is a relative fractional frequency stability of 5.2(3)×10-17τ-1/2 (where τ is the averaging time in seconds) for synchronous clock comparisons between sub-ensembles within the tweezer array. When further combined with the microscopic control and readout that are available in this system, these results pave the way towards long-lived engineered entanglement on an optical-clock transition13 in tailored atom arrays.

Light manipulation via spontaneous four-wave mixing in a warm double-Λ-type atomic ensemble.

We report on the dynamic manipulation of light in a warm 87Rb atomic ensemble using light storage based on the atomic spin coherence arising from the electromagnetically induced transparency (EIT) and spontaneous four-wave mixing (FWM) processes. We demonstrate that, subsequent to the generation of atomic spin coherence between two hyperfine ground states via the EIT storage process, it is possible to control the delay time, direction, and optical frequency of the retrieved light according to the timing sequence and powers of the coupling, probe, and driving lasers used for atomic-spin-coherence generation and the spontaneous FWM process. We believe that our results provide useful ideas in photon frequency conversion and photon control in connection with the quantum memories that is essential in the quantum communications technology.

Continuous-Variable Entanglement Adjustable by Phase Fluctuation and Classical Pumping Field in a Correlated Emission Laser Seeded with Squeezed Light

We present the influence of phase fluctuations on the entanglement and intensity of the radiation produced by a correlated-emission laser. The three-level atoms are initially prepared in a partial coherent superposition of the ground and exited states, and the driven radiation field incoming via the input mirror induces the atomic coherence that leads to the entanglement in the quantum system. The laser cavity also contains a nondegenerate parametric amplifier and is seeded by a two-mode squeezed light. The entanglement is analyzed by applying the Duan–Giedke–Cirac–Zoller (DGCZ) and logarithmic negativity inseparability criteria for a continuous variable system. We find that the phase fluctuation remarkably reduces the amount of entanglement in the weak driving field. On the other hand, the driven field completely overcomes the influence of phase fluctuations in the strong driving field, so that the entanglement remains in its highest degree (97%) in this regime.

Transcoherent States: Optical States for Maximal Generation of Atomic Coherence

Quantum technologies are built on the power of coherent superposition. Atomic coherence is typically generated from optical coherence, most often via Rabi oscillations. However, canonical coherent states of light create imperfect resources; a fully-quantized description of "$\tfrac{\pi}{2}$ pulses" shows that the atomic superpositions generated remain entangled with the light. We show that there are quantum states of light that generate coherent atomic states perfectly, with no residual atom-field entanglement. These states can be found for arbitrarily short times and approach slightly-number-squeezed $\tfrac{\pi}{2}$ pulses in the limit of large intensities; similar ideal states can be found for any $(2k+1)\tfrac{\pi}{2}$ pulses, requiring more number squeezing with increasing $k$. Moreover, these states can be repeatedly used as "quantum catalysts" to successfully generate coherent atomic states with high probability. From this perspective we have identified states that are "more coherent" than coherent states.

Frequency up-conversion of intense, ultrashort laser pulses at maximal atomic coherence

We present experimental data on adiabatically driven frequency conversion with ultrashort (picosecond) laser pulses towards the vacuum-ultraviolet regime, enhanced by coherent population return and preparation of maximal atomic coherences. We generate the sum frequency of an intense pump pulse and a probe pulse via a two-photon resonance in xenon. When we slightly detune the pump laser from two-photon resonance, the atomic populations are adiabatically driven forth and back from the atomic ground state to an excited state. This coherent population return (CPR) prepares the medium in a transient state of maximal atomic coherence, which enhances frequency mixing with a probe laser. We thoroughly study the variation of CPR-enhanced frequency conversion with experimental parameters and compare CPR with conventional, resonantly enhanced frequency conversion. In particular, we investigate the temporal evolution of the atomic coherence and the effect of inevitable ac Stark shifts. We find that ac Stark shifts induce an asymmetry in the spectral characteristics of CPR, which nevertheless permits enhanced frequency conversion. For the case of resonantly enhanced frequency conversion, we show that the atomic coherences are maintained for several tens of picoseconds after the pump pulse, which permits time-delayed frequency conversion. Moreover, we analyze the pressure dependence of the atomic coherence' lifetime and observe a free induction decay at the two-photon coherence with the generation of a second harmonic field. These findings shall push applications of adiabatic light-matter interactions also to the regime of nonlinear optics, driven by intense laser pulses.

Analysis of Controlled Rabi Flopping in a Double Rephasing Photon Echo Scheme for Quantum Memories.

A double rephasing scheme of a photon echo is analyzed for inversion-free photon echo-based quantum memories using controlled Rabi flopping, where the Rabi flopping is used for phase control of collective atom coherence. Unlike the rephasing-caused π-phase shift in a single rephasing scheme, the control Rabi flopping between the excited state and an auxiliary third state induces coherence inversion. Thus, the absorptive photon echo in a double rephasing scheme can be manipulated to be emissive. Here, we present a quantum coherence control of atom phases in a double rephasing photon echo scheme for emissive photon echoes for quantum memory applications.