1,697 research outputs found
Single-photon scattering on a two-qubit system. Spatio-temporal structure of the scattered field
In this paper, we study the spatiotemporal distribution of the photon
electric field produced by the scattering of a single photon narrow pulse from
a system of two identical qubits coupled to continuum modes in a
one-dimensional (1D) open waveguide. We derive the time-dependent dynamical
equations for qubits' and photon amplitudes which allow the calculation of the
photon backward and forward scattering fields in the whole space: before
qubits, between qubits, and behind the qubits. The scattered field consists of
several contributions that describe a free field of incoming photon, a
spontaneous exponential decay of excited qubits, a slowly decaying part that
dies out as the inverse powers of , and a lossless part that represents a
steady state solution as . For our system, we find the
transmittance and reflectance fields as both time and distance from the qubits
tend to infinity. We show that as the time after the event of scattering tends
to infinity, the steady state photon the field is being formed in the whole
one-dimensional space. If the distance between qubits is equal to the
integer of the wavelength , the field energy exhibits temporal
beatings between the qubit frequency and the photon frequency
with the period .Comment: 19 pages, 11 Figures, 39 Reference
Spontaneous decay of artificial atoms in a multi-qubit system
We consider a one-dimensional chain of N equidistantly spaced noninteracting
qubits embedded in an open waveguide. In the frame of single-excitation
subspace, we systematically study the evolution of qubits amplitudes if the
only qubit in the chain was initially excited. We show that the temporal
dynamics of qubits amplitudes crucially depend on the value of kd, where k is
the wave vector, d is a distance between neighbor qubits. If kd is equal to an
integer multiple of , then the qubits are excited to a stationary level
which scales as SN^{-1}S. We show that in this case, it is the dark states
which prevent qubits from decaying to zero even though they do not contribute
to the output spectrum of photon emission. For other values of kd the
excitations of qubits have the form of damping oscillations, which represent
the vacuum Rabi oscillations in a multi-qubit system. In this case, the output
spectrum of photon radiation is defined by a subradiant state with the smallest
width.Comment: 22 pages, 12 figures, 17 reference
Time- and frequency-domain polariton interference
We present experimental observations of interference between an atomic spin
coherence and an optical field in a {\Lambda}-type gradient echo memory. The
interference is mediated by a strong classical field that couples a weak probe
field to the atomic coherence through a resonant Raman transition. Interference
can be observed between a prepared spin coherence and another propagating
optical field, or between multiple {\Lambda} transitions driving a single spin
coherence. In principle, the interference in each scheme can yield a near unity
visibility.Comment: 11 pages, 5 figure
Gas Kinematics in the Magellanic-Type Galaxy NGC 7292
The paper presents results of studying the kinematics of the ionized gas in
the galaxy of the Large Magellanic Cloud type NGC 7292 obtained with the 2.5-m
telescope of the Caucasian Mountain Observatory (CMO SAI MSU) and the 6-m BTA
telescope of the Special Astrophysical Observatory (SAO RAS). Analysis of the
velocity fields of the ionized and neutral hydrogen showed that the kinematic
center of NGC 7292 located at the center of the bar, northwest of the
photometric center of the galaxy (the southeastern end of the bar) previously
taken as the center of NGC 7292. In addition to the circular rotation of the
gas, the radial motions associated with the bar play a significant role in the
kinematics of the disk. The observed perturbations of the gaseous-disk
kinematics induced by the ongoing star formation do not exceed those caused by
the bar. It is possible that part of the non-circular motions (at the
southeastern end of the bar which is the brightest HII region) may be related
to the effects of the capture of a dwarf companion or a gaseous cloud.Comment: Slightly edited version of the paper published in the Astrophysical
Bulletin. 10 pages, 8 figures, 1 tabl
Dynamical theory of single-photon transport through a qubit chain coupled to a one-dimensional nanophotonic waveguide
We study the dynamics of a single-photon pulse travelling through a linear
qubit chain coupled to continuum modes in a one-dimensional (1D) photonic
waveguide. We derive a time-dependent dynamical theory for qubit amplitudes and
for transmitted and reflected spectra. We show that the requirement for the
photon-qubit coupling to exist only for positive frequencies can significantly
change the dynamics of the system. First, it leads to an additional
photon-mediated dipole-dipole interaction between qubits which results in the
violation of the phase coherence between them. Second, the spectral lines of
transmitted and reflected spectra crucially depend on the shape of the incident
pulse and the initial distance between the pulse center and the first qubit in
the chain. We apply our theory to one-qubit and two-qubit systems. For these
two cases, we obtain the explicit expressions for the qubits' amplitudes and
the photon radiation spectra as time tends to infinity. For the incident
Gaussian wave packet we calculate the line shapes of transmitted and reflected
photons.Comment: 16 pages, 12 figures, 54 references. This version is the deeply
revized version of the previous paper Dynamical theory of single-photon
transport through a qubit chain coupled to a one-dimensional nanophotonic
waveguide. Beyond the Markovian approximatio
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