4,358 research outputs found
A Model for the Production of Regular Fluorescent Light from Coherently Driven Atoms
It has been shown in recent years that incoherent pumping through multiple
atomic levels provides a mechanism for the production of highly anti-bunched
light, and that as the number of incoherent steps is increased the light
becomes increasingly regular. We show that in a resonance fluorescence
situation, a multi-level atom may be multiply coherently driven so that the
fluorescent light is highly anti-bunched. We show that as the number of
coherently driven levels is increased, the spontaneous emissions may be made
increasingly more regular. We present a systematic method for designing the
level structure and driving required to produce highly anti-bunched light in
this manner for an arbitrary even number of levels.Comment: 6 pages multicol revtex, including figure
Squashed States of Light: Theory and Applications to Quantum Spectroscopy
Using a feedback loop it is possible to reduce the fluctuations in one
quadrature of an in-loop field without increasing the fluctuations in the
other. This effect has been known for a long time, and has recently been called
``squashing'' [B.C. Buchler et al., Optics Letters {\bf 24}, 259 (1999)], as
opposed to the ``squeezing'' of a free field in which the conjugate
fluctuations are increased. In this paper I present a general theory of
squashing, including simultaneous squashing of both quadratures and
simultaneous squeezing and squashing. I show that a two-level atom coupled to
the in-loop light feels the effect of the fluctuations as calculated by the
theory. In the ideal limit of light squeezed in one quadrature and squashed in
the other, the atomic decay can be completely suppressed.Comment: 8 pages plus one figure. Submitted to JEOS-B for Dan Walls Special
Issu
Entanglement of formation for symmetric Gaussian states
We show that for a fixed amount of entanglement, two-mode squeezed states are
those that maximize Einstein-Podolsky-Rosen-like correlations. We use this fact
to determine the entanglement of formation for all symmetric Gaussian states
corresponding to two modes. This is the first instance in which this measure
has been determined for genuine continuous variable systems.Comment: 4 pages, revtex
Crossover of phase qubit dynamics in presence of negative-result weak measurement
Coherent dynamics of a superconducting phase qubit is considered in the
presence of both unitary evolution due to microwave driving and continuous
non-unitary collapse due to negative-result measurement. In the case of a
relatively weak driving, the qubit dynamics is dominated by the non-unitary
evolution, and the qubit state tends to an asymptotically stable point on the
Bloch sphere. This dynamics can be clearly distinguished from conventional
decoherence by tracking the state purity and the measurement invariant
(``murity''). When the microwave driving strength exceeds certain critical
value, the dynamics changes to non-decaying oscillations: any initial state
returns exactly to itself periodically in spite of non-unitary dynamics. The
predictions can be verified using a modification of a recent experiment.Comment: 5 pages, 4 eps figure
Outcoupling from a Bose-Einstein condensate with squeezed light to produce entangled atom laser beams
We examine the properties of an atom laser produced by outcoupling from a
Bose-Einstein condensate with squeezed light. We model the multimode dynamics
of the output field and show that a significant amount of squeezing can be
transfered from an optical mode to a propagating atom laser beam. We use this
to demonstrate that two-mode squeezing can be used to produce twin atom laser
beams with continuous variable entanglement in amplitude and phase.Comment: 11 pages, 14 figure
The two-level atom laser: analytical results and the laser transition
The problem of the two-level atom laser is studied analytically. The
steady-state solution is expressed as a continued fraction, and allows for
accurate approximation by rational functions. Moreover, we show that the abrupt
change observed in the pump dependence of the steady-state population is
directly connected with the transition to the lasing regime. The condition for
a sharp transition to Poissonian statistics is expressed as a scaling limit of
vanishing cavity loss and light-matter coupling, , ,
such that stays finite and , where
is the rate of atomic losses. The same scaling procedure is also shown to
describe a similar change to Poisson distribution in the Scully-Lamb laser
model too, suggesting that the low-, low- asymptotics is of a more
general significance for the laser transition.Comment: 23 pages, 3 figures. Extended discussion of the paper aim (in the
Introduction) and of the results (Conclusions and Discussion). Results
unchange
High efficiency tomographic reconstruction of quantum states by quantum nondemolition measurements
We propose a high efficiency tomographic scheme to reconstruct an unknown
quantum state of the qubits by using a series of quantum nondemolition (QND)
measurements. The proposed QND measurements of the qubits are implemented by
probing the the stationary transmissions of the dispersively-coupled resonator.
It is shown that only one kind of QND measurements is sufficient to determine
all the diagonal elements of the density matrix of the detected quantum state.
The remaining non-diagonal elements of the density matrix can be determined by
other spectral measurements by beforehand transferring them to the diagonal
locations using a series of unitary operations. Compared with the pervious
tomographic reconstructions based on the usual destructively projective (DP)
measurements (wherein one kind of such measurements could only determine one
diagonal element of the density matrix), the present approach exhibits
significantly high efficiency for N-qubit (N > 1). Specifically, our generic
proposal is demonstrated by the experimental circuit-quantumelectrodynamics
(circuit-QED) systems with a few Josephson charge qubits.Comment: 9pages,4figure
Robust quantum gates on neutral atoms with cavity-assisted photon-scattering
We propose a scheme to achieve quantum computation with neutral atoms whose
interactions are catalyzed by single photons. Conditional quantum gates,
including an -atom Toffoli gate and nonlocal gates on remote atoms, are
obtained through cavity-assisted photon scattering in a manner that is robust
to random variation in the atom-photon coupling rate and which does not require
localization in the Lamb-Dicke regime. The dominant noise in our scheme is
automatically detected for each gate operation, leading to signalled errors
which do not preclude efficient quantum computation even if the error
probability is close to the unity.Comment: 4 pages, 3 figure
Measuring photon-photon interactions via photon detection
The strong non-linearity plays a significant role in physics, particularly,
in designing novel quantum sources of light and matter as well as in quantum
chemistry or quantum biology. In simple systems, the photon-photon interaction
can be determined analytically. However, it becomes challenging to obtain it
for more compex systems. Therefore, we show here how to measure strong
non-linearities via allowing the sample to interact with a weakly pumped
quantized leaking optical mode. We found that the detected mean-photon number
versus pump-field frequency shows several peaks. Interestingly, the interval
between neighbour peaks equals the photon-photon interaction potential.
Furthermore, the system exhibits sub-Poissonian photon statistics, entanglement
and photon switching with less than one photon. Finally, we connect our study
with existing related experiments.Comment: 4 pages, 3 figure
Squeezing enhancement by damping in a driven atom-cavity system
In a driven atom-cavity coupled system in which the two-level atom is driven
by a classical field, the cavity mode which should be in a coherent state in
the absence of its reservoir, can be squeezed by coupling to its reservoir. The
squeezing effect is enhanced as the damping rate of the cavity is increased to
some extent.Comment: 3 pages and 3 figure
- …