No Arabic abstract
A scheme for the detection of photons generated by vacuum mixing processes is proposed. The strategy consists in the utilization of a high numerical aperture parabolic mirror which tightly focuses two co-propagating laser beams with different frequencies. This produces a very high intensity region in the vicinity of the focus, where the photon-photon nonlinear interaction can then induce new electromagnetic radiation by wave mixing processes. These processes are investigated theoretically. The field at the focus is obtained from the Stratton-Chu vector diffraction theory, which can accomodate any configuration of an incoming laser beam. The number of photons generated is evaluated for an incident radially polarized beam. It is demonstrated that using this field configuration, vacuum mixing processes could be detected with envisaged laser technologies.
Recent progress in electro-optic sampling has allowed direct access to the fluctuations of the electromagnetic ground state. Here, we present a theoretical formalism that allows for an in-depth characterisation and interpretation of such quantum-vacuum detection experiments by relating their output statistics to the quantum statistics of the electromagnetic vacuum probed. In particular, we include the effects of absorption, dispersion and reflections from general environments. Our results agree with available experimental data while leading to significant corrections to previous theoretical predictions and generalises them to new parameter regimes. Our formalism opens the door for a detailed experimental analysis of the different characteristics of the polaritonic ground state, e.g. we show that transverse (free-field) as well as longitudinal (matter or near-field) fluctuations can be accessed individually by tuning the experimental parameters.
Controlling the quadrature measured by a homodyne detector is a universal task in continuous-variable quantum optics. However, deriving an error signal that is linear across theentire range of quadrature angles remains an open experimental problem. Here we propose a scheme to produce such an error signal through the use of a universally tunable modulator.
We demonstrate an unseeded, multimode four-wave mixing process in hot $^{85}$Rb vapor, using two pump beams of the same frequency that cross at a small angle. This results in the simultaneous fulfillment of multiple phase-matching conditions that reinforce one another to produce four intensity-stabilized bright output modes at two different frequencies. Each generated photon is directly correlated to exactly two others, resulting in the preferred four-mode output, in contrast to other multimode four-wave mixing experiments. This provides significant insight into the optimal configuration of the output multimode squeezed and entangled states generated in such four-wave mixing systems. We examine the power, temperature and frequency dependence of this new output and compare to the conical four-wave mixing emission from a single pump beam. The generated beams are spatially separated, allowing a natural distribution for potential use in quantum communication and secret-sharing protocols.
Entangled coherent states are shown to emerge, with high fidelity, when mixing coherent and squeezed vacuum states of light on a beam-splitter. These maximally entangled states, where photons bunch at the exit of a beamsplitter, are measured experimentally by Fock-state projections. Entanglement is examined theoretically using a Bell-type nonlocality test and compared with ideal entangled coherent states. We experimentally show nearly perfect similarity with entangled coherent states for an optimal ratio of coherent and squeezed vacuum light. In our scheme, entangled coherent states are generated deterministically with small amplitudes, which could be beneficial, for example, in deterministic distribution of entanglement over long distances.
We report on recent results obtained by analyzing axion--photon mixing in the framework of quantum field theory. We obtain corrections to the oscillation formulae and we reveal a new effect of the vacuum polarization due to the non-zero value of the vacuum energy for the component of the photon polarization mixed with the axion. The study of axion--photon mixing in curved space is also presented. Numerical analysis show that some quantum field theory effect of axion--photon mixing, in principle, could be detected experimentally.