95 research outputs found
Synthesis of the Einstein-Podolsky-Rosen entanglement in a sequence of two single-mode squeezers
Synthesis of the Einstein-Podolsky-Rosen entangled state --- the primary
entangled resource in continuous-variable quantum-optical information
processing --- is a technological challenge of great importance. Here we
propose and implement a new scheme of generating this state. Two nonlinear
optical crystals, positioned back-to-back in the waist of a pump beam, function
as single-pass degenerate optical parametric amplifiers and produce single-mode
squeezed vacuum states in orthogonal polarization modes, but in the same
spatiotemporal mode. A subsequent pair of waveplates acts as a beam splitter,
entangling the two polarization modes to generate the Einstein-Podolsky-Rosen
state. This technique takes advantage of the strong nonlinearity associated
with type-I phase-matching configuration while at the same time eliminating the
need for actively stabilizing the optical phase between the two squeezers,
which typically arises if these squeezers are spatially separated. We
demonstrate our method in an experiment, preparing a 1.4 dB two-mode squeezed
state and characterizing it via two-mode homodyne tomography.Comment: 4 pages, 3 figure
Undoing the effect of loss on quantum entanglement
Entanglement distillation is a process via which the strength and purity of
quantum entanglement can be increased probabilistically. It is a key step in
many quantum communication and computation protocols. In particular,
entanglement distillation is a necessary component of the quantum repeater, a
device which counters the degradation of entanglement that inevitably occurs
due to losses in a communication line. Here we report an experiment on
distilling the Einstein-Podolsky-Rosen (EPR) state of light, the workhorse of
continuous-variable entanglement, using the technique of noiseless
amplification. In contrast to previous implementations, the entanglement
enhancement factor achievable by our technique is not fundamentally limited and
permits recovering an EPR state with a macroscopic level of entanglement no
matter how low the initial entanglement or how high the loss may be. In
particular, we recover the original level of entanglement after one of the EPR
modes has passed through a channel with a loss factor of 20. The level of
entanglement in our distilled state is higher than that achievable by direct
transmission of any state through a similar loss channel. This is a key
bench-marking step towards the realization of a practical continuous-variable
quantum repeater and other CV quantum protocols.Comment: 8 pages, 5 figure
Numerical adiabatic potentials of orthorhombic Jahn-Teller effects retrieved from ultrasound attenuation experiments. Application to the SrF2:Cr crystal
A methodology is worked out to retrieve the numerical values of all the main
parameters of the six-dimensional adiabatic potential energy surface (APES) of
a polyatomic system with a quadratic T-term Jahn-Teller effect (JTE) from
ultrasound experiments. The method is based on a verified assumption that
ultrasound attenuation and speed encounter anomalies when the direction of
propa- gation and polarization of its wave of strain coincides with the
characteristic directions of symmetry breaking in the JTE. For the SrF2:Cr
crystal, employed as a basic example, we observed anomaly peaks in the
temperature dependence of attenuation of ultrasound at frequencies of 50-160
MHz in the temperature interval of 40-60 K for the wave propagating along the
[110] direction, for both the longitudinal and shear modes, the latter with two
polarizations along the [001] and [110] axes, respectively. We show that these
anomalies are due to the ultrasound relaxation by the system of non-interacting
Cr2+ JT centers with orthorhombic local distortions. The interpretation of the
ex- perimental findings is based on the T2g (eg +t2g) JTE problem including the
linear and quadratic terms of vibronic interactions in the Hamiltonian and the
same-symmetry modes reduced to one interaction mode. Combining the experimental
results with a theoretical analysis we show that on the complicated
six-dimensional APES of this system with three tetragonal, four trigonal, and
six orthorhombic extrema points, the latter are global minima, while the former
are saddle points, and we estimate numerically all the main parameters of this
surface, including the linear and quadratic vibronic coupling constants, the
primary force constants, the coordinates of all the extrema points and their
energies, the energy barrier between the orthorhombic minima, and the tunneling
splitting of the ground vibrational states.Comment: 8 pages, 3 figure
Activation Energy of the Jahn-Teller Complexes in CaF2:Cu2+ Crystal
In CaF2 crystal doped with Cu^2+ ions, attenuation of all the normal ultrasonic modes with the wave vector k // were investigated at 22 -163 MHz in the temperature region of 4 - 200 K
The Hubble Diagram to Redshift >6 from 69 Gamma-Ray Bursts
One of the few ways to measure the properties of Dark Energy is to extend the
Hubble daigram (HD) to higher redshifts with Gamma-Ray Bursts (GRBs). GRBs have
at least five properties (their spectral lag, variability, spectral peak photon
energy, time of the jet break, and the minimum rise time) which have
correlations to the luminosity of varying quality. In this paper, I construct a
GRB HD with 69 GRBs over a redshift range of 0.17 to >6, with half the bursts
having a redshift larger than 1.7. This paper uses over 3.6 times as many GRBs
and 12.7 times as many luminosity indicators as any previous GRB HD work. For
the gravitational lensing and Malmquist biases, I find that the biases are
small, with an average of 0.03 mag and an RMS scatter of 0.14 mag in the
distance modulus. The GRB HD is well-behaved and nicely delineates the shape of
the HD. The reduced chi-square for the fit to the concordance model is 1.05 and
the RMS scatter about the concordance model is 0.65 mag. This accuracy is just
a factor of 2.0 times that gotten for the same measure from all the big
supernova surveys. I fit the GRB HD to a variety of models, including where the
Dark Energy has its equation of state parameter varying as w(z)=w_0 + w_a
z/(1+z). I find that the concordance model is consistent with the data. That
is, the Dark Energy can be described well as a Cosmological Constant that does
not change with time. (abridged)Comment: ApJ in press, 88 pages, 15 figure
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