Superradiant lasing in inhomogeneously broadened ensembles with spatially varying coupling

Background: Theoretical studies of superradiant lasing on optical clock transitions predict a superb frequency accuracy and precision closely tied to the bare atomic linewidth. Such a superradiant laser is also robust against cavity fluctuations when the spectral width of the lasing mode is much larger than that of the atomic medium. Recent predictions suggest that this unique feature persists even for a hot and thus strongly broadened ensemble, provided the effective atom number is large enough. Methods: Here we use a second-order cumulant expansion approach to study the power, linewidth and lineshifts of such a superradiant laser as a function of the inhomogeneous width of the ensemble including variations of the spatial atom-field coupling within the resonator. Results: We present conditions on the atom numbers, the pump and coupling strengths required to reach the buildup of collective atomic coherence as well as scaling and limitations for the achievable laser linewidth. Conclusions: We show how sufficiently large numbers of atoms subject to strong optical pumping can induce synchronization of the atomic dipoles over a large bandwidth. This generates collective stimulated emission of light into the cavity mode leading to narrow-band laser emission at the average of the atomic frequency distribution. The linewidth is orders of magnitudes smaller than that of the cavity as well as the inhomogeneous gain broadening and exhibits reduced sensitivity to cavity frequency noise.

A Cold-Atom Interferometer with Microfabricated Gratings and a Single Seed Laser

The extreme miniaturization of a cold-atom interferometer accelerometer requires the development of novel technologies and architectures for the interferometer subsystems. We describe several component technologies and a laser system architecture to enable a path to such miniaturization. We developed a custom, compact titanium vacuum package containing a microfabricated grating chip for a tetrahedral grating magneto-optical trap (GMOT) using a single cooling beam. The vacuum package is integrated into the optomechanical design of a compact cold-atom sensor head with fixed optical components. In addition, a multichannel laser system driven by a single seed laser has been implemented with time-multiplexed frequency shifting using single sideband modulators, reducing the number of optical channels connected to the sensor head. This laser system architecture is compatible with a highly miniaturized photonic integrated circuit approach, and by demonstrating atom-interferometer operation with this laser system, we show feasibility for the integrated photonic approach. In the compact sensor head, sub-Doppler cooling in the GMOT produces 15 μK temperatures, which can operate at a 20 Hz data rate for the atom interferometer sequence. After validating atomic coherence with Ramsey interferometry, we demonstrate a light-pulse atom interferometer in a gravimeter configuration without vibration isolation for 10 Hz measurement cycle rate and T = 0 - 4.5 ms interrogation time, resulting in Δg/g = 2.0e-6. All these efforts demonstrate progress towards deployable cold-atom inertial sensors under large amplitude motional dynamics.

Superradiant lasing in inhomogeneously broadened ensembles with spatially varying coupling

Background: Theoretical studies of superradiant lasing on optical clock transitions predict a superb frequency accuracy and precision closely tied to the bare atomic linewidth. Such a superradiant laser is also robust against cavity fluctuations when the spectral width of the lasing mode is much larger than that of the atomic medium. Recent predictions suggest that this unique feature persists even for a hot and thus strongly broadened ensemble, provided the effective atom number is large enough. Methods: Here we use a second-order cumulant expansion approach to study the power, linewidth and lineshifts of such a superradiant laser as a function of the inhomogeneous width of the ensemble including variations of the spatial atom-field coupling within the resonator. Results: We present conditions on the atom numbers, the pump and coupling strengths required to reach the buildup of collective atomic coherence as well as scaling and limitations for the achievable laser linewidth. Conclusions: We show how sufficiently large numbers of atoms subject to strong optical pumping can induce synchronization of the atomic dipoles over a large bandwidth. This generates collective stimulated emission of light into the cavity mode leading to narrow-band laser emission at the average of the atomic frequency distribution. The linewidth is orders of magnitudes smaller than that of the cavity as well as the inhomogeneous gain broadening and exhibits reduced sensitivity to cavity frequency noise.

Nonclassical Atomic System Dynamics Time-dependently Interacts With Finite Entangled Pair Coherent Parametric Converter Cavity Fields

We consider a time-dependent model that describes a qubit time-dependently interacts with a cavity containing finite entangled pair coherent parametric converter fields. The dynamics of some quantum phenomena, as: phase space information, quantum entanglement and squeezing, are explored by atomic Husimi function, atomic Wehrl entropy, variance, and entropy squeezing. The influences of the unitary qubit-cavity interaction, the difference between the two-mode photon numbers, the initial atomic coherence, and the time-dependent qubit location are investigated. It is found that the regularity, the amplitudes and the frequency of the quantum phenomena can be controlled by the physical parameters. For the initial atomic pure state, the qubit-cavity entanglement, the qubit phase space information, and atomic squeezing can be generated strongly compared to those of the initial atomic mixed state. The time-dependent location parameters enhance the generated quantum phenomena, and its effect can be enhanced by the parameters of the two-mode photon numbers and the initial atomic coherence.

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.