Here, we describe progress toward realization of a vector magnetometer based on all-optical excitation
of an atomic ensemble in a vapor cell under the conditions of electromagnetically induced transparency (EIT). The EIT resonance amplitudes depend on relative orientations of the three key vectors: laser wave-vector, polarization,
and the direction of the magnetic field. By analyzing possible two-photon transitions and their combinations, we can,
in principle, analytically calculate the amplitude of various EIT resonances as functions of the relative angles between
the magnetic field, polarization and laser propagation vectors. By locking the polarization to
one of these maxima, one can determine the plane formed by the magnetic field and the light wave vector to the
accuracy better than 0.001 rad. Analysis of the relative resonance amplitude may be used to extract the full information
about the magnetic field direction.
If one has access to information about a quantum system both before and after a measurement, the usual remit of Heisenberg uncertainty relation (HUR) does not apply. Here, we theoretically and experimentally demonstrate that, in such a scenario, one can retrodict position and momentum measurements without being limited by HUR. The experiment uses a large ensemble of 10^11 atoms in a macroscopic vapor cell, and the results may be applicable for quantum state estimation and sensing, especially for sensitive magnetometers equally capable of measuring the amplitude and phase of an RF magnetic field both below the standard quantum limit.
Quantum interface between photons is a long- standing goal of fundamental significance, and also serves as powerful tools for quantum technologies. Remarkable advances in quantum optics have recently developed in several platforms to demonstrate the generation of optical nonlinearities at the level of individual photons, which enable a number of unique applications such as light-by-light control at quantum level. Here, we present two examples in the realm of continuous variables based on the platform of flying atoms where thermal motion of atoms with long-lived coherence of ground state mediate the coupling between the spatially separated optical channels.
We investigate a four-wave-mixing process in an N interaction scheme in Rb vapor placed inside a low-finesse ring cavity. We observe strong amplification and generation of a probe signal, circulating in the cavity, in the presence of two strong optical pump fields. We study the variations in probe field gain and dispersion as functions of experimental parameters with an eye on the potential application of such a system for enhanced rotation measurements. Density-matrix calculations are performed to model the system and are shown to provide good qualitative agreement with the experiment.
We investigate weak optical probe pulse propagation in a resonant Lambda and N-interaction schemes, and investigate the role of the four-wave mixing on classical and quantum properties of the probe field. In particular, we focus our attention on two configurations. In the first case we take into account the off-resonant coupling of the strong field to the signal field ground state. Such configuration is relevant for EIT-based slow light and quantum memory. In the second configuration the additional control field is derived from an independent laser, and it is tuned to a different optical resonance from the ones forming an original Lambda system. Such interaction scheme allows realization of tunable slow and fast light, and was considered with regards to enhancement of optical gyroscopes performance.
We demonstrate that in both cases the four-wave mixing (FWM) has a profound effect on signal field group velocity and absorption profile, and may even lead to gain. We present both semi-classical and fully quantum treatments for propagation of both signal and newly generated Stokes fields that include accurate description of their quantum noise. In particular, we analyze the case of a quadrature-squeezed signal field, and demonstrate that vacuum fluctuations of the Stokes field couple into the signal field through the FWM process and degrades the squeezing. The severity of this degradation grows with optical depths of an atomic medium, setting an additional practical limits for the experiments.
We investigate the propagation of a weak probe laser field in a medium of warm Rb atoms, controlled with two strong resonant pump fields tuned to the D1 and D2 optical transitions to form an N-scheme arrangement. We have shown theoretically that four-wave mixing has a profound effect on the probe-field group velocity and absorption, allowing the probe-field propagation to be continuously tuned from superluminal to slow-light regimes with amplification. We have also identified the experimental conditions for observation of such tunable slow-to-fast light regime (continuously through the point of zero group index) with positive probe-field gain, and demonstrated that the spectral range corresponding to the zero group index can be tuned by controlling the power of one of the pump laser.
In this manuscript we present calculations that consider the propagation of a squeezed vacuum signal field through
a resonant atomic medium under electromagnetically induced transparency (EIT). We show that squeezing is
degraded due to four-wave mixing processes at high optical depth of the atomic medium. We also present some
preliminary results for degenerate Zeeman EIT resonances.
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