1,101 research outputs found
Stable control of 10 dB two-mode squeezed vacuum states of light
Continuous variable entanglement is a fundamental resource for many quantum
information tasks. Important protocols like superactivation of zero-capacity
channels and finite-size quantum cryptography that provides security against
most general attacks, require about 10 dB two-mode squeezing. Additionally,
stable phase control mechanisms are necessary but are difficult to achieve
because the total amount of optical loss to the entangled beams needs to be
small. Here, we experimentally demonstrate a control scheme for two-mode
squeezed vacuum states at the telecommunication wavelength of 1550 nm. Our
states exhibited an Einstein-Podolsky-Rosen covariance product of 0.0309 \pm
0.0002, where 1 is the critical value, and a Duan inseparability value of 0.360
\pm 0.001, where 4 is the critical value. The latter corresponds to 10.45 \pm
0.01 dB which reflects the average non-classical noise suppression of the two
squeezed vacuum states used to generate the entanglement. With the results of
this work demanding quantum information protocols will become feasible.Comment: 8 pages, 4 figure
Quantum Interference of Photon Pairs from Two Trapped Atomic Ions
We collect the fluorescence from two trapped atomic ions, and measure quantum
interference between photons emitted from the ions. The interference of two
photons is a crucial component of schemes to entangle atomic qubits based on a
photonic coupling. The ability to preserve the generated entanglement and to
repeat the experiment with the same ions is necessary to implement entangling
quantum gates between atomic qubits, and allows the implementation of protocols
to efficiently scale to larger numbers of atomic qubits.Comment: 4 pages, 4 figure
Two Color Entanglement
We report on the generation of entangled states of light between the
wavelengths 810 and 1550 nm in the continuous variable regime. The fields were
produced by type I optical parametric oscillation in a standing-wave cavity
build around a periodically poled potassium titanyl phosphate crystal, operated
above threshold. Balanced homodyne detection was used to detect the
non-classical noise properties, while filter cavities provided the local
oscillators by separating carrier fields from the entangled sidebands. We were
able to obtain an inseparability of I=0.82, corresponding to about -0.86 dB of
non-classical quadrature correlation.Comment: 4 pages, 2 figure
Time domain Einstein-Podolsky-Rosen correlation
We experimentally demonstrate creation and characterization of
Einstein-Podolsky-Rosen (EPR) correlation between optical beams in the time
domain. The correlated beams are created with two independent continuous-wave
optical parametric oscillators and a half beam splitter. We define temporal
modes using a square temporal filter with duration and make time-resolved
measurement on the generated state. We observe the correlations between the
relevant conjugate variables in time domain which correspond to the EPR
correlation. Our scheme is extendable to continuous variable quantum
teleportation of a non-Gaussian state defined in the time domain such as a
Schr\"odinger cat-like state.Comment: 4 pages, 4 figure
Generation of ultrabright tunable polarization entanglement without spatial, spectral, or temporal constraints
The need for spatial and spectral filtering in the generation of polarization
entanglement is eliminated by combining two coherently-driven type-II
spontaneous parametric downconverters. The resulting ultrabright source emits
photon pairs that are polarization entangled over the entire spatial cone and
spectrum of emission. We detect a flux of 12 000 polarization-entangled
pairs/s per mW of pump power at 90% quantum-interference visibility, and the
source can be temperature tuned for 5 nm around frequency degeneracy. The
output state is actively controlled by precisely adjusting the relative phase
of the two coherent pumps.Comment: 10 pages, 5 figure
Experimental generation of 6 dB continuous variable entanglement from a nondegenerate optical parametric amplifier
We experimentally demonstrated that the quantum correlations of amplitude and
phase quadratures between signal and idler beams produced from a non-degenerate
optical parametric amplifier (NOPA) can be significantly improved by using a
mode cleaner in the pump field and reducing the phase fluctuations in phase
locking systems. Based on the two technical improvements the quantum
entanglement measured with a two-mode homodyne detector is enhanced from ~ 4 dB
to ~ 6 dB below the quantum noise limit using the same NOPA and nonlinear
crystal.Comment: 7 pages, 5 figure
Cascaded Entanglement Enhancement
We present a cascaded system consisting of three non-degenerate optical
parametric amplifiers (NOPAs) for the generation and the enhancement of quantum
entanglement of continuous variables. The entanglement of optical fields
produced by the first NOPA is successively enhanced by the second and the third
NOPAs from -5.3 to -8.1 below the quantum noise limit. The dependence
of the enhanced entanglement on the physical parameters of the NOPAs and the
reachable entanglement limitation for a given cascaded NOPA system are
calculated. The calculation results are in good agreement with the experimental
measurements.Comment: 5 pages, 4 figure
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