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Showing papers on "Atomic coherence published in 2020"


Journal ArticleDOI
17 Dec 2020-Nature
TL;DR: This work leverages the favourable properties of tweezer-trapped alkaline-earth (strontium-88) atoms and introduces a hybrid approach to tailoring optical potentials that balances scalability, high-fidelity state preparation, site-resolved readout and preservation of atomic coherence.
Abstract: 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 of leading 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. A tweezer clock containing about 150 88Sr atoms achieves trapping and optical excited-state lifetimes exceeding 40 seconds, and shows relative fractional frequency stability similar to that of leading atomic clocks.

117 citations


Journal ArticleDOI
TL;DR: In this article, a Tavis-Cummings model was used to characterize the velocity-dependent dynamics of the atoms as well as the dependency on the cavity detuning, and the authors experimentally and theoretically characterized the lasing threshold and evolution of such a system.
Abstract: Highly stable laser sources based on narrow atomic transitions provide a promising platform for direct generation of stable and accurate optical frequencies. Here we investigate a simple system operating in the high-temperature regime of cold atoms. The interaction between a thermal ensemble of $^{88}\mathrm{Sr}$ at mK temperatures and a medium-finesse cavity produces strong collective coupling and facilitates high atomic coherence, which causes lasing on the dipole forbidden $^{1}S_{0}\ensuremath{\leftrightarrow}^{3}P_{1}$ transition. We experimentally and theoretically characterize the lasing threshold and evolution of such a system and investigate decoherence effects in an unconfined ensemble. We model the system using a Tavis-Cummings model and characterize the velocity-dependent dynamics of the atoms as well as the dependency on the cavity detuning.

59 citations


Journal ArticleDOI
TL;DR: In this article, a hybrid approach was proposed to tailoring optical potentials that balances scalability, high-fidelity state preparation, site-resolved readout, and preservation of atomic coherence.
Abstract: The preparation of large, low-entropy, highly coherent ensembles of identical quantum systems is foundational for many studies in quantum metrology, simulation, and information. Here, we realize these features by leveraging the favorable properties of tweezer-trapped alkaline-earth atoms while introducing a new, 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 $10^{16}$. These coherence times and atom numbers reduce the effect of quantum projection noise to a level that is on par with leading atomic systems, yielding a relative fractional frequency stability of $5.2(3)\times10^{-17}~(\tau/s)^{-1/2}$ for synchronous clock comparisons between sub-ensembles within the tweezer array. When further combined with the microscopic control and readout available in this system, these results pave the way towards long-lived engineered entanglement on an optical clock transition in tailored atom arrays.

20 citations


Journal ArticleDOI
TL;DR: A collection of cold rubidium atoms in three-level configuration trapped in one dimensional optical lattice is revisited and strong evidence that the nonreciprocal behavior can be greatly enhanced by increasing the spatial modulation amplitude is shown.
Abstract: A collection of cold rubidium atoms in three-level configuration trapped in one dimensional (1D) optical lattice is revisited. The trapped atoms are considered in the Gaussian density distribution and study the realization of P T-, non-P T- and P T anti-symmetry in optical susceptibility in 1D atomic lattices in a periodic structure. Such a fascinating modulation is achieved by spatially modulating the intensity of the driving field. Interestingly, a nonreciprocal optical propagation phenomenon is investigated. In this system, we have introduced a microwave that couples to the two ground states, spatial modulation of the coupling field, and the atomic density with Gaussian distribution in practice. With a proper detuning and coupling field Rabi frequencies, we can find the condition of P T-symmetry along with field propagation direction, and the novel properties of transmission and reflections have been discussed. The large difference of field reflections from the two ends of the atomic lattice medium shows strong evidence that the nonreciprocal behavior can be greatly enhanced by increasing the spatial modulation amplitude.

13 citations


Journal ArticleDOI
29 Oct 2020
TL;DR: More coherent than coherent states: Novel quantum states of light are optimal for creating coherent superposition of qubit states as discussed by the authors, which is the state of the art for quantum superposition.
Abstract: More coherent than coherent states: Novel quantum states of light are optimal for creating coherent superposition of qubit states.

11 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of phase fluctuations on the entanglement and intensity of the radiation produced by a correlated-emission laser was analyzed by applying the Duan-Giedke-Cirac-Zoller (DGCZ) and logarithmic negativity inseparability criteria for a continuous variable system.
Abstract: 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.

10 citations


Journal ArticleDOI
TL;DR: In this article, the authors theoretically study the generation of orbital angular momentum (OAM) based on the four-wave mixing process in a diamond-type homogeneously broadened 85Rb atomic system.
Abstract: We theoretically study the generation of orbital angular momentum (OAM) based on the four-wave mixing process in a diamond-type homogeneously broadened 85Rb atomic system. We use density matrix formalism at a weak field limit to explain the origin of vortex translation between different optical fields and a generated signal. We show how the singularities, which are omnipresent in the phases of the input optical vortex beams, can be profoundly mapped to atomic coherence in the transverse plane, which holds the origin of OAM translation. This translation process works well even for a moderately intense probe and control field, which enhances medium nonlinearity. The generation and manipulation of OAM of the light beam in a nonlinear medium may have important applications in optical tweezers and quantum information processing systems.

9 citations


Journal ArticleDOI
TL;DR: An efficient scheme for realizing all-optical router or beam splitter by employing a double tripod-type atomic system, where the ground levels are coupled by two additional intensity-dependent weak microwave fields, showing that the high-dimensional probe field encoded in a degree of freedom of orbital angular momentum can be stored, retrieved, and manipulated.
Abstract: 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.

7 citations


Journal ArticleDOI
TL;DR: In this paper, the transfer of optical vortices is studied based on double two-photon processes in a four-level diamond configuration system, where a pair of strong fields are applied to prepare atomic coherence, while two weak probe fields are coupled with the other two transitions.
Abstract: The transfer of optical vortices is studied based on double two-photon processes in a four-level diamond configuration system. A pair of strong fields are applied to prepare atomic coherence, while two weak probe fields are coupled with the other two transitions. When the two-photon resonances are satisfied, the analytical results for the intensities of the probe fields are calculated using perturbation theory and an adiabatic approximation approach. Our results explore whether the orbital angular momentum of an input probe beam or the second control field can be transferred to the generated probe field, and this is verified by numerical simulation. It is interesting that as the intensities of the control fields increase, the propagation of probe beams exhibits oscillation behaviors only when the one-photon detuning is nonzero. Furthermore, we show that the absorption losses are minimized, and the transfer efficiency is enhanced by appropriately modifying the one-photon detuning together with the control-field Rabi frequencies.

6 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that an optical field in a two-mode squeezed vacuum state can propagate through a lossy atomic medium without degradation or evolution, and that the losses give rise to that state when a different state is initially injected into the medium.
Abstract: We show that, under certain circumstances, an optical field in a two-mode squeezed vacuum (TMSV) state can propagate through a lossy atomic medium without degradation or evolution. Moreover, the losses give rise to that state when a different state is initially injected into the medium. Such a situation emerges in a Λ-type atomic system, in which both optical transitions are driven by strong laser fields that are two-photon resonant with the respective signal modes. Then the interactions of the two signal modes with the ground-state atomic coherence interfere destructively, thereby ensuring the preservation of the TMSV with a particular squeezing parameter. This mechanism permits unified interpretation of recent experimental results and predicts new phenomena.

5 citations


Journal ArticleDOI
TL;DR: In this article, a femtosecond (fs) pump-probe scheme and measuring directional emission signals was used to investigate the excited-state dynamics of hydrogen (H) atoms in flames, and it was shown that the behavior of the atomic system involves atomic coherence, which is produced nonadiabatically and corresponds to a superradiant process.
Abstract: We investigate the excited-state dynamics of hydrogen (H) atoms in flames by using a femtosecond (fs) pump-probe scheme and measuring directional emission signals. An approximately 100-fs pump pulse at 205.1 nm excites H atoms through a two-photon process (n = 3 ←← n = 1), which is followed by detection of the forward emission signals induced by a broadband fs probe pulse near 656 nm. Above a certain threshold, we observe a quadratic dependence of the emission signal on the pump laser energy. Moreover, the linewidth of the forward emission signal varies with the probe delay and the probe laser energy. This behavior can be explained in terms of superradiance. We perform a theoretical analysis and compare the experimental results with the theory, and conclude that, within the conditions of our experiment, the behavior of the atomic system involves atomic coherence, which is produced non-adiabatically and corresponds to a superradiant process. Variations in the duration of the gain time window and lifetime of the excited-state H atoms in flames are explored at different flame conditions (i.e., equivalence ratio and heights above the burner). The fs pump-probe technique demonstrated here can also be extended to characterize the time-resolved population dynamics and the corresponding collisional energy transfer rates for energy levels involved in laser-induced fluorescence detection of H atoms in flames relevant to practical combustion applications.

Journal ArticleDOI
TL;DR: It is demonstrated 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, the form of the eigenstate of an atom coupled to a cavity mode displaying a three-dimensional periodic profile is obtained, and it is shown that the quantized motion leads to degenerate states where the atomic degrees of freedom are masked, that is, upon detection of one component of this composite system the others remain in an entangled state.
Abstract: The form of the eigenstates of an atom coupled to a cavity mode displaying a three-dimensional periodic profile are obtained. It is shown that the quantized motion leads to degenerate states where the atomic degrees of freedom are masked, that is, upon detection of one component of this composite system the others remain in an entangled state. When the system is extended to include drive and dissipation it is found to undergo a dissipative quantum phase transition at a critical drive amplitude. Unlike other phase transitions reported in the literature, the degeneracy prepares the system in a superposition of incompatible states upon detection of the electromagnetic field. Probing the field hints at an order above the transition point that, due to state masking, allows for atomic coherence to survive at long times.

Journal ArticleDOI
TL;DR: In this article, the authors studied the squeezing spectrum of the fluorescence field emitted from a four-level atom in a configuration driven by two coherent fields and found that the squeezing properties were significantly influenced by the presence of vacuum-induced coherence in the atomic system.
Abstract: The squeezing spectrum of the fluorescence field emitted from a four-level atom in $J=1/2$ to $J=1/2$ configuration driven by two coherent fields is studied. We find that the squeezing properties of the fluorescence radiation are significantly influenced by the presence of vacuum-induced coherence in the atomic system. It is shown that such coherence induces spectral squeezing in phase quadratures of the fluorescence light for both weak and strong driving fields. The dependence of the squeezing spectrum on the relative phase of the driving fields is also investigated. Effects such as enhancement or suppression of the squeezing peaks are shown in the spectrum as the relative phase is varied. An analytical explanation of the numerical findings is presented using dressed-states of the atom-field system.

Journal ArticleDOI
15 Feb 2020
TL;DR: In this article, the authors show that the character of the observed intensity noise in any output polarization basis can be modeled as a Markov process in the input light fields' amplitudes that excite the response of a three-level medium.
Abstract: Intensity noise cross-correlation of the polarization eigenstates of light emerging from an atomic vapor cell in the Hanle EIT configuration results in high resolution spectroscopy even with free-running semiconductor lasers. We show that the character of the observed intensity noise in any output polarization basis can be modeled as a Markov process in the input light fields’ amplitudes that excite the response of a three-level medium. This method has promise as an inexpensive and simpler approach to vector magnetometry and has applications in timekeeping and as a probe of dynamics of atomic coherence in warm vapor cells.

Journal ArticleDOI
TL;DR: In this paper, the authors 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.
Abstract: 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.

Proceedings ArticleDOI
TL;DR: In this paper, the feasibility of carrier-envelope phase (CEP) detection using few-cycle pulse pairs is numerically analyzed in a two-level system, and much lower power requirement is demonstrated in comparison with single-pulse schemes.
Abstract: The feasibility of carrier-envelope phase (CEP) detection using few-cycle pulse pairs is numerically analyzed in a two-level system. Much lower power requirement is demonstrated in comparison with single-pulse schemes.


Posted Content
TL;DR: In this paper, coherent control of entangled photon-pair emission in electron-atom collisions mediated by transfer of the temporal and atomic coherence carried by the incident electron wave packet was investigated.
Abstract: Two-pathway coherent control of photoionization is an example of control of matter waves using light. Here, we analyze the opposite and investigate the control of quantum light using matter waves. We report coherent control of entangled photon-pair emission in electron-atom collisions mediated by transfer of the temporal and atomic coherence carried by the incident electron wave packet. The latter is engineered by resonantly-enhanced multiphoton ionization exploiting interfering ionization pathways. We show that both sources of coherence can be used to control the angular distributions of photons emitted by radiative cascade upon optical decay in the target atom, offering the possibility of coherent control driven by sculpted matter waves via transfer of optical and atomic coherence.

Proceedings ArticleDOI
02 Nov 2020
TL;DR: Theoretical simulation and experimental researches of the phenomena of induced superradiation are curried out as mentioned in this paper, and theoretical simulations of the phenomenon of super-radiation have been carried out.
Abstract: Theoretical simulation and experimental researches of the phenomena of induced superradiation are curried out.

Journal ArticleDOI
27 Dec 2020
TL;DR: In this paper, the authors 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, the steady optical properties of triple quantum dots, which obtain a tunneling-induced effect by using the external electric field, were investigated and it was shown that the electromagnetically induced transparency can be achieved via the tunneling induced effect.
Abstract: We investigated the steady optical properties of the triple quantum dots, which obtain a tunneling-induced effect by using the external electric field. Our numerical results shown that the electromagnetically induced transparency can be achieved via the tunneling-induced effect. In addition, we examined the propagation dynamics of a probe field in this system and found that the probe field group velocities and their absorption were related to the tunneling coupling intensities. This finding allowed us to control the probe field to obtain ultraslow group velocities and a tunable optical switch. Finally, using this scheme it was possible to store and release the probe field by modulating the tunneling coupling sequences.

Journal ArticleDOI
TL;DR: In this paper, it was shown that there are quantum states of light that generate coherent atomic states perfectly, with no residual atom-field entanglement, and these states can be found for arbitrarily short times and approach slightly number-squeezed $2k+1/$π 2π 2 ϵ 2π ϵ pulses in the limit of large intensities, requiring more number squeezing with increasing ϵ.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, the authors studied spin fluctuations of room-temperature neutral atoms in a Bell-Bloom type magnetometer and found a strong asymmetry in the noise distribution of the atomic signal quadratures at the magnetic resonance.
Abstract: Spin noise spectroscopy is emerging as a powerful technique for studying the dynamics of various spin systems also beyond their thermal equilibrium and linear response. Here, we study spin fluctuations of room-temperature neutral atoms in a Bell-Bloom type magnetometer. Driven by indirect pumping and undergoing a parametric excitation, this system is known to produce noise-squeezing. Our measurements not only reveal a strong asymmetry in the noise distribution of the atomic signal quadratures at the magnetic resonance, but also provide insight into the mechanism behind its generation and evolution. In particular, a structure in the spectrum is identified which allows to investigate the main dependencies and the characteristic timescales of the noise process. The results obtained are compatible with parametrically induced noise squeezing. Notably, the noise spectrum provides information on the spin dynamics even in regimes where the macroscopic atomic coherence is lost, effectively enhancing the sensitivity of the measurements. Our work promotes spin noise spectroscopy as a versatile technique for the study of noise squeezing in a wide range of spin based magnetic sensors.