173 research outputs found
Real-time detection of individual atoms falling through a high-finesse optical cavity
The enhanced coupling between atoms and photons inside a high-finesse optical cavity provides a novel basis for optical measurements that continuously monitor atomic degrees of freedom. We describe an experiment in which cavity quantum-electrodynamic effects are utilized for real-time detection of individual atoms falling through an optical cavity after being dropped from a magneto-optical trap. Our technique permits experiments that are triggered by the presence of a single optimally coupled atom within the cavity mode volume
Nonlinear spectroscopy in the strong-coupling regime of cavity QED
A nonlinear spectroscopic investigation of a strongly coupled atom-cavity system is presented. A two-field pump-probe experiment is employed to study nonlinear structure as the average number of intracavity atoms is varied from NÌ
â4.2 to NÌ
â0.8. Nonlinear effects are observed for as few as 0.1 intracavity pump photons. A detailed semiclassical simulation of the atomic beam experiment gives reasonable agreement with the data for NÌ
âł2 atoms. The simulation procedure accounts for fluctuations in atom-field coupling which have important effects on both the linear and nonlinear probe transmission spectra. A discrepancy between the simulations and the experiments is observed for small numbers of atoms (NÌ
âČ1). Unfortunately, it is difficult to determine if this discrepancy is a definitive consequence of the quantum nature of the atom-cavity coupling or a result of the severe technical complications of the experiment
Near-field imaging with two transmission gratings for submicrometer localization of atoms
We show theoretically that an atomic pattern with period d can be obtained with 100% visibility even for an infinitely extended source by sending atoms through two transmission gratings with periods d and d/2, respectively, and separated by half the Talbot length LT/2=d^2/2λdB, where λdB is the atomic wavelength and the source is infinitely far away. For a finite source distance, as would be attainable in any real experiment, a small correction to the grating periods and separations restores the period-d pattern. This effect is closely related to the Talbot and Lau effects in classical optics and can be used to localize atoms to a submicrometer scale without a compromise in atomic flux. We first derive compact analytical formulas for the idealized case of a monochromatic source and large gratings and then verify numerically that a finite grating size and velocity dispersion in the beam do not decrease the fringe visibility considerably. Finally, we briefly present an experiment in preparation to exhibit this localization
Quantum phase gate for photonic qubits using only beam splitters and post-selection
We show that a beam splitter of reflectivity one-third can be used to realize
a quantum phase gate operation if only the outputs conserving the number of
photons on each side are post-selected.Comment: 6 pages RevTex, including one figur
Two-photon nonlinearity in general cavity QED systems
We have investigated the two-photon nonlinearity at general cavity QED
systems, which covers both weak and strong coupling regimes and includes
radiative loss from the atom. The one- and two-photon propagators are obtained
in analytic forms. By surveying both coupling regimes, we have revealed the
conditions on the photonic wavepacket for yielding large nonlinearity depending
on the cavity Q-value. We have also discussed the effect of radiative loss on
the nonlinearity.Comment: 8 pages, 5 figure
Coupling of effective one-dimensional two-level atoms to squeezed light
A cavity QED system is analyzed which duplicates the dynamics of a two-level
atom in free space interacting exclusively with broadband squeezed light. We
consider atoms in a three or four-level Lambda-configuration coupled to a
high-finesse optical cavity which is driven by a squeezed light field. Raman
transitions are induced between a pair of stable atomic ground states via the
squeezed cavity mode and coherent driving fields. An analysis of the reduced
master equation for the atomic ground states shows that a three-level atomic
system has insufficient parameter flexibility to act as an effective two-level
atom interacting exclusively with a squeezed reservoir. However, the inclusion
of a fourth atomic level, coupled dispersively to one of the two ground states
by an auxiliary laser field, introduces an extra degree of freedom and enables
the desired interaction to be realised. As a means of detecting the reduced
quadrature decay rate of the effective two-level system, we examine the
transmission spectrum of a weak coherent probe field incident upon the cavity
Complete Characterization of a Quantum Process: the Two-Bit Quantum Gate
We show how to fully characterize a quantum process in an open quantum
system. We particularize the procedure to the case of a universal two-qubit
gate in a quantum computer. We illustrate the method with a numerical
simulation of a quantum gate in the ion trap quantum computer.Comment: Accepted for publication in Physical Review Letters 08Nov96
(submitted 15Jly96
Measurement of conditional phase shifts for quantum logic
Measurements of the birefringence of a single atom strongly coupled to a
high-finesse optical resonator are reported, with nonlinear phase shifts
observed for intracavity photon number much less than one. A proposal to
utilize the measured conditional phase shifts for implementing quantum logic
via a quantum-phase gate (QPG) is considered. Within the context of a simple
model for the field transformation, the parameters of the "truth table" for the
QPG are determined.Comment: 4 pages in Postscript format, including 4 figures (attached as
uuencoded version of a gzip-file
Quantum-Information Processing with Semiconductor Macroatoms
An all optical implementation of quantum information processing with
semiconductor macroatoms is proposed. Our quantum hardware consists of an array
of semiconductor quantum dots and the computational degrees of freedom are
energy-selected interband optical transitions. The proposed quantum-computing
strategy exploits exciton-exciton interactions driven by ultrafast sequences of
multi-color laser pulses. Contrary to existing proposals based on charge
excitations, the present all-optical implementation does not require the
application of time-dependent electric fields, thus allowing for a
sub-picosecond, i.e. decoherence-free, operation time-scale in realistic
state-of-the-art semiconductor nanostructures.Comment: 11 pages, 5 figures, to be published in Phys. Rev. Lett., significant
changes in the text and new simulations (figure 3
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