4,346 research outputs found
Parametric Oscillation with Squeezed Vacuum Reservoirs
Employing the quantum Hamiltonian describing the interaction of two-mode
light (signal-idler modes) generated by a nondegenerate parametric oscillator
(NDPO) with two uncorrelated squeezed vacuum reservoirs (USVR), we derive the
master equation. The corresponding Fokker-Planck equation for the Q-function is
then solved employing a propagator method developed in Ref. \cite{1}. Making
use of this Q-function, we calculate the quadrature fluctuations of the optical
system. From these results we infer that the signal-idler modes are in squeezed
states and the squeezing occurs in the first quadrature. When the NDPO operates
below threshold we show that, for a large squeezing parameter, a squeezing
amounting to a noise suppression approaching 100% below the vacuum level in the
first quadrature can be achieved.Comment: 16 page
Quantum-dot-spin single-photon interface
Using background-free detection of spin-state-dependent resonance
fluorescence from a single-electron charged quantum dot with an efficiency of
0:1%, we realize a single spin-photon interface where the detection of a
scattered photon with 300 picosecond time resolution projects the quantum dot
spin to a definite spin eigenstate with fidelity exceeding 99%. The bunching of
resonantly scattered photons reveals information about electron spin dynamics.
High-fidelity fast spin-state initialization heralded by a single photon
enables the realization of quantum information processing tasks such as
non-deterministic distant spin entanglement. Given that we could suppress the
measurement back-action to well below the natural spin-flip rate, realization
of a quantum non-demolition measurement of a single spin could be achieved by
increasing the fluorescence collection efficiency by a factor exceeding 20
using a photonic nanostructure
Influence of External Fields and Environment on the Dynamics of Phase Qubit-Resonator System
We analyze the dynamics of a qubit-resonator system coupled with a thermal
bath and external electromagnetic fields. Using the evolution equations for the
set of Heisenberg operators, that describe the whole system, we derive an
expression for the resonator field, accounting for the resonator-drive,-bath,
and -qubit interaction. The renormalization of the resonator frequency, caused
by the qubit-resonator interaction, is accounted for. Using solutions for the
resonator field, we derive the equation describing qubit dynamics. The
influence of the qubit evolution during the measurement time on the fidelity of
a single-shot measurement is studied. The relation between the fidelity and
measurement time is shown explicitly. Also, an expression describing relaxation
of the superposition qubit state towards its stationary value is derived. The
possibility of controlling this state, by varying the amplitude and frequency
of drive, is shown.Comment: 15 page
Coherent state LOQC gates using simplified diagonal superposition resource states
In this paper we explore the possibility of fundamental tests for coherent
state optical quantum computing gates [T. C. Ralph, et. al, Phys. Rev. A
\textbf{68}, 042319 (2003)] using sophisticated but not unrealistic quantum
states. The major resource required in these gates are state diagonal to the
basis states. We use the recent observation that a squeezed single photon state
() approximates well an odd superposition of coherent
states () to address the diagonal resource
problem. The approximation only holds for relatively small and hence
these gates cannot be used in a scaleable scheme. We explore the effects on
fidelities and probabilities in teleportation and a rotated Hadamard gate.Comment: 21 pages, 12 figure
Hierarchy of integrable Hamiltonians describing of nonlinear n-wave interaction
In the paper we construct an hierarchy of integrable Hamiltonian systems
which describe the variation of n-wave envelopes in nonlinear dielectric
medium. The exact solutions for some special Hamiltonians are given in terms of
elliptic functions of the first kind.Comment: 17 page
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
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
Quantum dynamics in single spin measurement
We study the quantum dynamics of a model for the single-spin measurement in
magnetic-resonance force microscopy. We consider an oscillating driven
cantilever coupled with the magnetic moment of the sample. Then, the cantilever
is damped through an external bath and its readout is provided by a radiation
field. Conditions for reliable measurements will be discussed.Comment: 7 pages, 3 figure
Synchronization of many nano-mechanical resonators coupled via a common cavity field
Using amplitude equations, we show that groups of identical nano-mechanical
resonators, interacting with a common mode of a cavity microwave field,
synchronize to form a single mechanical mode which couples to the cavity with a
strength dependent on the square sum of the individual mechanical-microwave
couplings. Classically this system is dominated by periodic behaviour which,
when analyzed using amplitude equations, can be shown to exhibit
multi-stability. In contrast groups of sufficiently dissimilar nano-mechanical
oscillators may lose synchronization and oscillate out of phase at
significantly higher amplitudes. Further the method by which synchronization is
lost resembles that for large amplitude forcing which is not of the Kuramoto
form.Comment: 23 pages, 11 figure
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