We report our progress towards a high performance solid-state ring laser gyro using a diode-pumped Nd-YAG crystal as the gain medium. We then discuss the possibility of including in this device a highly dispersive medium, which could serve for testing the recent proposal by Shariar and coworkers of a fast-light ring laser gyro. This discussion is supported in particular by the recent results obtained at Laboratoire Aimé Cotton with electromagnetically induced transparency in metastable helium
We optimize the simultaneous oscillations at two frequencies in a class-A Vertical External Cavity Surface Emitting
Laser (VECSEL). We perform this task by measuring the coupling constant between the two perpendicular polarized
modes for different values of the transverse spatial separation between the two modes.
The nearest-neighbor entanglement of the evolved state of an asymmetric quantum XY spin chain, in a transverse time-dependent
field, exhibits criticalities (dynamical phase transitions) as the initial field parameter is varied at a given fixed
time. After a discussion of the dynamical phase transition, we investigate the extent to which the role of an information-theoretic
quantum correlation measure, called quantum discord, can be used to understand the entanglement dynamics in
this spin model. We show that quantum discord can be associated with the collapse and revival of nearest-neighbor
entanglement exhibited in the critical behavior. This behavior of quantum discord leads to the broader question of
whether certain classes of measures of nonclassical correlation can help to understand the non-generic features of
entanglement in a given system.
We experimentally study two different tripod configurations using metastable <sup>4</sup>He, with the probe perpendicular and
parallel to the quantization axis, defined by an applied weak magnetic field. In the first case, the two dark resonances
interact incoherently and merge together into a single transparency peak with increasing coupling power. In the second
case, we observe destructively interfering double dark resonances leading to a narrow absorption dip at the line center.
We confirm the results theoretically.
We present a realistic theoretical treatment of a three-level Λ system in a hot atomic vapor interacting with a
coupling and a probe field of arbitrary strengths, leading to electromagnetically-induced transparency and slow
light under the two-photon resonance condition. We take into account all the relevant decoherence processes
including collisions. Velocity-changing collisions (VCCs) are modeled in the strong collision limit effectively,
which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. We take into
account a dynamic rate of influx of atoms in the two lower levels of the Λ, and an outflux from all the three
levels. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the
experimentally measured response characteristics. Our predictions are in excellent agreement with the reported
experimental results for <sup>4</sup>He*. The role played by the VCC parameter is seen to be distinct from that by the
transit time or Raman coherence decay rate.
In a Λ-type atomic system with electromagnetically-induced transparency, we probe the fidelity of the storage
and retrieval of an electromagnetic signal, as the control laser field is varied with time. We study numerically the
adiabatic transfer problem for an isolated atom, and show that for a weak signal, even the slowest variations of
the control field take the system out of the dark state, which is a coherent superposition of the two lower levels
of the Λ system. Following this, we incorporate the effect of dissipation on system dynamics by allowing for
spontaneous decay of the system to the lower levels in a wavefunction approach. We conclude that dissipation
definitely aids the retrieval process but not so much the storage. Further, for storing the signal, the control field
should be switched off as slowly as possible, but while retrieving it, the faster we switch on the control field, the
better the signal is retrieved. Also, for a given system there is an optimal control power for the best retrieval.
Our results find partial support in the reported experimental observations.