517 research outputs found
5A2--Theory of the optical parametric oscillator
A formalism for describing optical parametric oscillation is developed. The theory is applied to the derivation of the oscillation threshold condition, power output, the Manley-Rowe conditions, index matching, and frequency tuning
Simple quantum feedback of a solid-state qubit
We propose an experiment on quantum feedback control of a solid-state qubit,
which is almost within the reach of the present-day technology. Similar to the
earlier proposal, the feedback loop is used to maintain the coherent (Rabi)
oscillations in a qubit for an arbitrary long time; however, this is done in a
significantly simpler way, which requires much smaller bandwidth of the control
circuitry. The main idea is to use the quadrature components of the noisy
detector current to monitor approximately the phase of qubit oscillations.
The price for simplicity is a less-than-ideal operation: the fidelity is
limited by about 95%. The feedback loop operation can be experimentally
verified by appearance of a positive in-phase component of the detector current
relative to an external oscillating signal used for synchronization.Comment: 5 page
Theory of emission from an active photonic lattice
The emission from a radiating source embedded in a photonic lattice is
calculated. The analysis considers the photonic lattice and free space as a
combined system. Furthermore, the radiating source and electromagnetic field
are quantized. Results show the deviation of the photonic lattice spectrum from
the blackbody distribution, with intracavity emission suppressed at certain
frequencies and enhanced at others. In the presence of rapid population
relaxation, where the photonic lattice and blackbody populations are described
by the same equilibrium distribution, it is found that the enhancement does not
result in output intensity exceeding that of the blackbody at the same
frequency. However, for slow population relaxation, the photonic lattice
population has a greater tendency to deviate from thermal equilibrium,
resulting in output intensities exceeding those of the blackbody, even for
identically pumped structures.Comment: 19 pages, 11 figure
Non-Markovian disentanglement dynamics of two-qubit system
We investigated the disentanglement dynamics of two-qubit system in
Non-Markovian approach. We showed that only the couple strength with the
environment near to or less than fine-structure constant 1/137, entanglement
appear exponential decay for a certain class of two-qubit entangled state.
While the coupling between qubit and the environment is much larger, system
always appears the sudden-death of entanglement even in the vacuum environment.Comment: 17 pages, 3 figure
Wave mixing of optical pulses and Bose-Einstein condensates
We investigate theoretically the four-wave mixing of optical and matter waves
resulting from the scattering of a short light pulse off an atomic
Bose-Einstein condensate, as recently demonstrated by D. Schneble {\em et al.}
[ Science {\bf 300}, 475 (2003)]. We show that atomic ``pair production'' from
the condensate results in the generation of both forward- and
backward-propagating matter waves. These waves are characterized by different
phase-matching conditions, resulting in different angular distributions and
temporal evolutions.Comment: 4+\epsilon pages, 3 figure
Quantification of Macroscopic Quantum Superpositions within Phase Space
Based on phase-space structures of quantum states, we propose a novel measure
to quantify macroscopic quantum superpositions. Our measure simultaneously
quantifies two different kinds of essential information for a given quantum
state in a harmonious manner: the degree of quantum coherence and the effective
size of the physical system that involves the superposition. It enjoys
remarkably good analytical and algebraic properties. It turns out to be the
most general and inclusive measure ever proposed that it can be applied to any
types of multipartite states and mixed states represented in phase space.Comment: 4 pages, 1 figure, accepted for publication in Phys. Rev. Let
Dependence of the evolution of the cavity radiation of a coherently pumped correlated emission laser on dephasing and phase fluctuation
Analysis of the dynamics of the cavity radiation of a coherently pumped
correlated emission laser is presented. The phase fluctuation and dephasing are
found to affect the time evolution of the two-mode squeezing and intensity of
the cavity radiation significantly. The intensity and degree of the two-mode
squeezing increase at early stages of the process with time, but this trend
changes rapidly afterwards. It is also shown that they increase with phase
fluctuation and dephasing in the strong driving limit, however the situation
appears to be opposite in the weak driving limit. This essentially suggests
that the phase fluctuation and dephasing weaken the coherence induced by a
strong driving mechanism so that the spontaneous emission gets a chance. The
other important aspect of the phase fluctuation, in this regard, is the
relaxation of the time at which the maximum squeezing is manifested as well as
the time in which the radiation remains in a squeezed state.Comment: 10 pages, 12 figure
Photon number states generated from a continuous-wave light source
Conditional preparation of photon number states from a continuous-wave
nondegenerate optical parametric oscillator is investigated. We derive the
phase space Wigner function for the output state conditioned on photo detection
events that are not necessarily simultaneous, and we maximize its overlap with
the desired photon number state by choosing the optimal temporal output state
mode function. We present a detailed numerical analysis for the case of
two-photon state generation from a parametric oscillator driven with an
arbitrary intensity below threshold, and in the low intensity limit, we present
a formalism that yields the optimal output state mode function and fidelity for
higher photon number states.Comment: 8 pages, 7 figures, v2: shortened versio
A temperature behavior of the frustrated translational mode of adsorbate and the nature of the "adsorbate-substrate" interaction
A temperature behavior of the frustrated translational mode (T-mode) of a
light particle, coupled by different regimes of ohmicity to the surface, is
studied within a formalism of the generalized diffusion coefficients. The
memory effects of the adsorbate motion are considered to be the main reason of
the T-mode origin. Numerical calculations yield a thermally induced shift and
broadening of the T-mode, which is found to be linear in temperature for Ohmic
and super-Ohmic systems and nonlinear for strongly sub-Ohmic ones. We obtain
analytical expressions for the T-mode shift and width at weak coupling for the
systems with integer "ohmicity" indexes n=0-2 in zero temperature and high
temperature limits. We provide an explanation of the experimentally observed
blue- or red-shifts of the T-mode on the basis of a comparative analysis of two
typical times of the system evolution: a time of decay of the
"velocity-velocity" autocorrelation function, and a correlation time of the
thermal bath random forces. A relation of the T-mode to the multiple jumps of
the adsorbate is discussed, and generalization of conditions of the multiple
hopping to the case of quantum surface diffusion is performed.Comment: 12 pages, 4 figure
Opacity of electromagnetically induced transparency for quantum fluctuations
We analyze the propagation of a pair of quantized fields inside a medium of
three-level atoms in configuration. We calculate the stationary
quadrature noise spectrum of the field after propagating through the medium, in
the case where the probe field is in a squeezed state and the atoms show
electromagnetically induced transparency (EIT). We find an oscillatory transfer
of the initial quantum properties between the probe and pump fields which is
most strongly pronounced when both fields have comparable Rabi frequencies.
This implies that the quantum state measured after propagation can be
completely different from the initial state, even though the mean values of the
field are unaltered
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