Frank Vewinger

Instant single-photon Fock state tomography

Heralded single photons are prepared at a rate of approximately 100 kHz via conditional measurements on polarization-nondegenerate biphotons produced in a periodically poled potassium-titanyl phosphate crystal. The single-photon Fock state is characterized using high-frequency pulsed optical homodyne tomography with a fidelity of (57.6+/-0.1)%. The state preparation and detection rates allowed us to perform on-the-fly alignment of the apparatus based on real-time analysis of the quadrature measurement statistics.

Adiabatic frequency conversion of optical information in atomic vapor

We experimentally demonstrate a communication protocol that enables frequency conversion and routing of quantum information in an adiabatic and thus robust way. The protocol is based on electromagnetically induced transparency (EIT) in systems with multiple excited levels: transfer and/or distribution of optical states between different signal modes is implemented by adiabatically changing the control fields. The proof-of-principle experiment is performed using the hyperfine levels of the rubidium D1 line.

Time-resolved probing of the ground state coherence in rubidium.

We demonstrate the preparation and probing of the coherence between the hyperfine ground states |S(1/2),F=1> and |5S(1/2),F=2> of the Rb87 isotope. The effects of various coherence control techniques, i.e., fractional stimulated Raman adiabatic passage and coherent population return, on the coherence are investigated. These techniques are implemented using nearly degenerate pump and Stokes lasers at 795 nm (Rb D1 transition), which couple the two hyperfine ground states via the excited state |5P(1/2),F=1> through a resonant two-photon process in which a coherent superposition of the two hyperfine ground states is established. The medium is probed by an additional weak laser, which generates a four-wave mixing signal proportional to the ground state coherence and allows us to monitor its evolution in time. The experimental data are compared with numerical simulations.

Characterization of atomic coherence decay for storage of light experiments

We report characterization of EIT resonances in the D1 line of Rb 87 under various experimental conditions. The dependence of the EIT linewidth on the power of the control field investigated. Strictly linear behavior between the ground levels as the main source of decoherence. We therefore formulated a new theory assuming pure dephasing to be the main decoherence mechanism. We also performed experiments where we created additional decoherence mechanisms by means of a counter-propagating repumper field. This field caused the ground-state population exchange, thus reproducing conditions in which the original theory is valid.

Electromagnetically-Induced Transparency with Classical and Nonclassical Light

We present our progress towards storage of squeezed light by means of electromagnetically-induced transparency as well as protocols for routing, frequency conversion, and geometric steering of optical modes in atomic systems with multiple excited levels.

Characterization of atomic coherence decay for the storage of light

We present an experimental study of decoherence of the ground energy levels of 87Rb atoms in vapor cells. We measure the decoherence of the ground state using three different methods: measuring the decay constant of the storage of light in atomic vapor, the decay rates of transient coherence oscillations of the ground state, and the width of the electromagnetically induced transparency resonances. The measurements showed decoherence rates on the scale of 104 s-1.

Adiabatic Transfer of Quantum Optical Information in Atomic Vapor

We demonstrate a quantum communication protocol (RATOS) that enables frequency conversion and routing of quantum optical information in an adiabatic and robust way. The protocol is based on EIT in systems with multiple excited levels. Article not available.