6,951 research outputs found
Lasing in circuit quantum electrodynamics with strong noise
We study a model which can describe a superconducting single electron
transistor (SSET) or a double quantum dot coupled to transmission-line
oscillator. In both cases the degree of freedom is given by a charged particle,
which couples strongly to the electromagnetic environment or phonons. We
consider the case where a lasing condition is established and study the
dependence of the average photon number in the resonator on the spectral
function of the electromagnetic environment. We focus on three important cases:
a strongly coupled environment with a small cut-off frequency, a structured
environment peaked at a specific frequency and 1/f-noise. We find that the
electromagnetic environment can have a substantial impact on the photon
creation. Resonance peaks are in general broadened and additional resonances
can appear
Broadband squeezed light from phase-locked single-mode sub-Poissonian lasers
We consider sub-Poissonian single-mode laser with external synchronization
and analyze its applicability to the problems of quantum information. Using
Heisenberg-Langevin theory we calculate the quadrature variances of the field
emitted by this laser. It is shown that such systems can demonstrate strong
quadrature squeezing. Taking into account that the emitted field is temporally
multi-mode the application of such sources to multichannel quantum
teleportation and dense coding protocols is discussed.Comment: 14 pages, 7 figure
Quantal Brownian Motion - Dephasing and Dissipation
We analyze quantal Brownian motion in dimensions using the unified model
for diffusion localization and dissipation, and Feynman-Vernon formalism. At
high temperatures the propagator possess a Markovian property and we can write
down an equivalent Master equation. Unlike the case of the
Zwanzig-Caldeira-Leggett model, genuine quantum mechanical effects manifest
themselves due to the disordered nature of the environment. Using Wigner
picture of the dynamics we distinguish between two different mechanisms for
destruction of coherence. The analysis of dephasing is extended to the low
temperature regime by using a semiclassical strategy. Various results are
derived for ballistic, chaotic, diffusive, both ergodic and non-ergodic motion.
We also analyze loss of coherence at the limit of zero temperature and clarify
the limitations of the semiclassical approach. The condition for having
coherent effect due to scattering by low-frequency fluctuations is also pointed
out. It is interesting that the dephasing rate can be either larger or smaller
than the dissipation rate, depending on the physical circumstances.Comment: LaTex, 23 pages, 4 figures, published vesio
Irreversibility on the Level of Single-Electron Tunneling
We present a low-temperature experimental test of the fluctuation theorem for
electron transport through a double quantum dot. The rare entropy-consuming
system trajectories are detected in the form of single charges flowing against
the source-drain bias by using time-resolved charge detection with a quantum
point contact. We find that these trajectories appear with a frequency that
agrees with the theoretical predictions even under strong nonequilibrium
conditions, when the finite bandwidth of the charge detection is taken into
account
Statistics of voltage fluctuations in resistively shunted Josephson junctions
The intrinsic nonlinearity of Josephson junctions converts Gaussian current
noise in the input into non-Gaussian voltage noise in the output. For a
resistively shunted Josephson junction with white input noise we determine
numerically exactly the properties of the few lowest cumulants of the voltage
fluctuations, and we derive analytical expressions for these cumulants in
several important limits. The statistics of the voltage fluctuations is found
to be Gaussian at bias currents well above the Josephson critical current, but
Poissonian at currents below the critical value. In the transition region close
to the critical current the higher-order cumulants oscillate and the voltage
noise is strongly non-Gaussian. For coloured input noise we determine the third
cumulant of the voltage.Comment: 9 pages, 5 figure
Electron transport through interacting quantum dots
We present a detailed theoretical investigation of the effect of Coulomb
interactions on electron transport through quantum dots and double barrier
structures connected to a voltage source via an arbitrary linear impedance.
Combining real time path integral techniques with the scattering matrix
approach we derive the effective action and evaluate the current-voltage
characteristics of quantum dots at sufficiently large conductances. Our
analysis reveals a reach variety of different regimes which we specify in
details for the case of chaotic quantum dots. At sufficiently low energies the
interaction correction to the current depends logarithmically on temperature
and voltage. We identify two different logarithmic regimes with the crossover
between them occurring at energies of order of the inverse dwell time of
electrons in the dot. We also analyze the frequency-dependent shot noise in
chaotic quantum dots and elucidate its direct relation to interaction effects
in mesoscopic electron transport.Comment: 21 pages, 4 figures. References added, discussion slightly extende
Laser theory in manifest Lindblad form
We discuss the laser theory for a single-mode laser with nonlinear gain. We
focus in particular on a micromaser which is pumped with a dilute beam of
excited atoms crossing the laser cavity. In the weak-coupling regime, an
expansion in the coupling strength is developed that preserves the Lindblad
form of the master equation, securing the positivity of the density matrix.
This expansion breaks rapidly down above threshold. This can be improved with
an alternative approach, not restricted to weak coupling: the Lindblad
operators are expanded in orthogonal polynomials adapted to the probability
distribution for the atom-laser interaction time. Results for the photon
statistics and the laser linewidth illustrate the theory.Comment: 13 pages, 8 figures, to be published in J Phys B (minor revision
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