53 research outputs found
Experimental demonstration of entanglement assisted coding using a two-mode squeezed vacuum state
We have experimentally realized the scheme initially proposed as quantum
dense coding with continuous variables [Ban, J. Opt. B \textbf{1}, L9 (1999),
and Braunstein and Kimble, \pra\textbf{61}, 042302 (2000)]. In our experiment,
a pair of EPR (Einstein-Podolski-Rosen) beams is generated from two independent
squeezed vacua. After adding two-quadrature signal to one of the EPR beams, two
squeezed beams that contain the signal were recovered. Although our squeezing
level is not sufficient to demonstrate the channel capacity gain over the
Holevo limit of a single-mode channel without entanglement, our channel is
superior to conventional channels such as coherent and squeezing channels. In
addition, optical addition and subtraction processes demonstrated are
elementary operations of universal quantum information processing on continuous
variables.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Generation of large-amplitude coherent-state superposition via ancilla-assisted photon-subtraction
We propose and demonstrate a novel method to generate a large-amplitude
coherent-state superposition (CSS) via ancilla-assisted photon-subtraction. The
ancillary mode induces quantum interference of indistinguishable processes,
widening the controllability of quantum superposition at the conditional
output. We demonstrate the concept in the time domain, by a simple
time-separated two-photon subtraction from cw squeezed light. We observe the
largest CSS ever reported without any corrections, which will enable various
quantum information applications with CSS states.Comment: 5 pages, 4 figures; the revised versio
Experimental verification of a fully inseparable tripartite continuous-variable state
A continuous-variable tripartite entangled state is experimentally generated
by combining three independent squeezed vacuum states and the variances of its
relative positions and total momentum are measured. We show that the measured
values violate the separability criteria based on the sum of these quantities
and prove the full inseparability of the generated state.Comment: 5 pages, 4 figure
Experimental demonstration of quantum teleportation of a squeezed state
Quantum teleportation of a squeezed state is demonstrated experimentally. Due
to some inevitable losses in experiments, a squeezed vacuum necessarily becomes
a mixed state which is no longer a minimum uncertainty state. We establish an
operational method of evaluation for quantum teleportation of such a state
using fidelity, and discuss the classical limit for the state. The measured
fidelity for the input state is 0.85 0.05 which is higher than the
classical case of 0.730.04. We also verify that the teleportation process
operates properly for the nonclassical state input and its squeezed variance is
certainly transferred through the process. We observe the smaller variance of
the teleported squeezed state than that for the vacuum state input.Comment: 7 pages, 1 new figure, comments adde
Optimization of quantum noise in space gravitational-wave antenna DECIGO with optical-spring quantum locking considering mixture of vacuum fluctuations in homodyne detection
Quantum locking using optical spring and homodyne detection has been devised
to reduce quantum noise that limits the sensitivity of DECIGO, a space-based
gravitational wave antenna in the frequency band around 0.1 Hz for detection of
primordial gravitational waves. The reduction in the upper limit of energy
density from to
, as inferred from recent observations, necessitates
improved sensitivity in DECIGO to meet its primary science goals. To accurately
evaluate the effectiveness of this method, this paper considers a detection
mechanism that takes into account the influence of vacuum fluctuations on
homodyne detection. In addition, an advanced signal processing method is
devised to efficiently utilize signals from each photodetector, and design
parameters for this configuration are optimized for the quantum noise. Our
results show that this method is effective in reducing quantum noise, despite
the detrimental impact of vacuum fluctuations on its sensitivity.Comment: 12 pages, 5 figure
The Subaru Deep Field Project: Lyman Emitters at Redshift of 6.6
We present new results of a deep optical imaging survey using a narrowband
filter () centered at 9196 \AA ~ together with , ,
, , and broadband filters in the sky area of the Subaru
Deep Field which has been promoted as one of legacy programs of the 8.2m Subaru
Telescope. We obtained a photometric sample of 58 Ly emitter candidates
at 6.5 -- 6.6 among strong -excess () objects together with a color criterion of . We then obtained optical spectra of 20 objects in our -excess
sample and identified at least nine Ly emitters at -- 6.6
including the two emitters reported by Kodaira et al. (2003). Since our
Ly emitter candidates are free from strong amplification of
gravitational lensing, we are able to discuss their observational properties
from a statistical point of view. Based on these new results, we obtain a lower
limit of the star formation rate density of yr Mpc at , being
consistent with our previous estimate. We discuss the nature of star-formation
activity in galaxies beyond .Comment: 49 pages, 16 figures, PASJ, Vol. 57, No. 1, in pres
First-step experiment in developing optical-spring quantum locking for DECIGO: sensitivity optimization for simulated quantum noise by completing the square
DECi-hertz Interferometer Gravitational Wave Observatory (DECIGO) is a future
mission for a space-borne laser interferometer. DECIGO has 1,000-km-long arm
cavities mainly to detect the primordial gravitational waves (PGW) at lower
frequencies around 0.1 Hz. Observations in the electromagnetic spectrum have
lowered the bounds on the upper limit of PGW energy density (). As a result, DECIGO's target sensitivity, which
is mainly limited by quantum noise, needs further improvement. To maximize the
feasibility of detection while constrained by DECIGO's large diffraction loss,
a quantum locking technique with an optical spring was theoretically proposed
to improve the signal-to-noise ratio of the PGW. In this paper, we
experimentally verify one key element of the optical-spring quantum locking:
sensitivity optimization by completing the square of multiple detector outputs.
This experiment is operated on a simplified tabletop optical setup with
classical noise simulating quantum noise. We succeed in getting the best of the
sensitivities with two different laser powers by the square completion method.Comment: 10 pages, 14 figure
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