124 research outputs found
Vacuum-Stimulated Raman Scattering based on Adiabatic Passage in a High-Finesse Optical Cavity
We report on the first observation of stimulated Raman scattering from a
Lambda-type three-level atom, where the stimulation is realized by the vacuum
field of a high-finesse optical cavity. The scheme produces one intracavity
photon by means of an adiabatic passage technique based on a counter-intuitive
interaction sequence between pump laser and cavity field. This photon leaves
the cavity through the less-reflecting mirror. The emission rate shows a
characteristic dependence on the cavity and pump detuning, and the observed
spectra have a sub-natural linewidth. The results are in excellent agreement
with numerical simulations.Comment: 4 pages, 5 figure
Quantum Beat of Two Single Photons
The interference of two single photons impinging on a beam splitter is
measured in a time-resolved manner. Using long photons of different frequencies
emitted from an atom-cavity system, a quantum beat with a visibility close to
100% is observed in the correlation between the photodetections at the output
ports of the beam splitter. The time dependence of the beat amplitude reflects
the coherence properties of the photons. Most remarkably, simultaneous
photodetections are never observed, so that a temporal filter allows one to
obtain perfect two-photon coalescence even for non-perfect photons.Comment: 4 pages, 3 figure
Entanglement and purity of single- and two-photon states
Whereas single- and two-photon wave packets are usually treated as pure
states, in practice they will be mixed. We study how entanglement created with
mixed photon wave packets is degraded. We find in particular that the
entanglement of a delocalized single-photon state of the electro-magnetic field
is determined simply by its purity. We also discuss entanglement for two-photon
mixed states, as well as the influence of a vacuum component.Comment: 11 pages, 10 figures, 1 debuting autho
Detecting drift of quantum sources: not the de Finetti theorem
We propose and analyze a method to detect and characterize the drift of a
nonstationary quantum source. It generalizes a standard measurement for
detecting phase diffusion of laser fields to quantum systems of arbitrary
Hilbert space dimension, qubits in particular. We distinguish diffusive and
systematic drifts, and examine how quickly one can determine that a source is
drifting. We show that for single-photon wavepackets our measurement is
implemented by the Hong-Ou-Mandel effect.Comment: 5 pages, 2 figure
Characterization of single photons using two-photon interference
Adiabatic passage techniques allow the generation of single photons which are
very long compared to the typical detector time resolution. Therefore the
detection time of a photon can be measured within the duration of the
single-photon wavepacket. As a consequence, two-photon interference can be
investigated in a time-resolved manner, i.e., the coincidence rate can be
measured as a function of the time between photodetections. The theoretical
analysis shows that this method not only gives information about the duration
of single photons, but also about their coherence time. Here we discuss how to
use this method for a spectral or temporal characterization of a single-photon
source.Comment: 17 pages, 12 figure
Counter-Intuitive Vacuum-Stimulated Raman Scattering
Vacuum-stimulated Raman scattering in strongly coupled atom-cavity systems
allows one to generate free-running single photon pulses on demand. Most
properties of the emitted photons are well defined, provided spontaneous
emission processes do not contribute. Therefore, electronic excitation of the
atom must not occur, which is assured for a system adiabatically following a
dark state during the photon-generation process. We experimentally investigate
the conditions that must be met for adiabatic following in a time-of-flight
driven system, with atoms passing through a cavity and a pump beam oriented
transverse to the cavity axis. From our results, we infer the optimal intensity
and relative pump-beam position with respect to the cavity axis.Comment: 4 pages, 4 figure
- …