20 research outputs found
Quantum teleportation of light beams
We experimentally demonstrate quantum teleportation for continuous variables
using squeezed-state entanglement. The teleportation fidelity for a real
experimental system is calculated explicitly, including relevant imperfection
factors such as propagation losses, detection inefficiencies and phase
fluctuations. The inferred fidelity for input coherent states is F = 0.61 +-
0.02, which when corrected for the efficiency of detection by the output
observer, gives a fidelity of 0.62. By contrast, the projected result based on
the independently measured entanglement and efficiencies is 0.69. The
teleportation protocol is explained in detail, including a discussion of
discrepancy between experiment and theory, as well as of the limitations of the
current apparatus.Comment: 17 pages, 19 figures, submitted to PR
Equivalent efficiency of a simulated photon-number detector
Homodyne detection is considered as a way to improve the efficiency of
communication near the single-photon level. The current lack of commercially
available {\it infrared} photon-number detectors significantly reduces the
mutual information accessible in such a communication channel. We consider
simulating direct detection via homodyne detection. We find that our particular
simulated direct detection strategy could provide limited improvement in the
classical information transfer. However, we argue that homodyne detectors (and
a polynomial number of linear optical elements) cannot simulate photocounters
arbitrarily well, since otherwise the exponential gap between quantum and
classical computers would vanish.Comment: 4 pages, 4 figure
Optimal States for Bell inequality Violations using Quadrature Phase Homodyne Measurements
We identify what ideal correlated photon number states are to required to
maximize the discrepancy between local realism and quantum mechanics when a
quadrature homodyne phase measurement is used. Various Bell inequality tests
are considered.Comment: 6 pages, 5 Figure
Creating Bell states and decoherence effects in quantum dots system
We show how to improve the efficiency for preparing Bell states in coupled
two quantum dots system. A measurement to the state of driven quantum laser
field leads to wave function collapse. This results in highly efficiency
preparation of Bell states. The effect of decoherence on the efficiency of
generating Bell states is also discussed in this paper. The results show that
the decoherence does not affect the relative weight of and in the
output state, but the efficiency of finding Bell states.Comment: 4 pages, 2figures, corrected some typo
Quantum cryptography using balanced homodyne detection
We report an experimental quantum key distribution that utilizes balanced
homodyne detection, instead of photon counting, to detect weak pulses of
coherent light. Although our scheme inherently has a finite error rate, it
allows high-efficiency detection and quantum state measurement of the
transmitted light using only conventional devices at room temperature. When the
average photon number was 0.1, an error rate of 0.08 and "effective" quantum
efficiency of 0.76 were obtained.Comment: Errors in the sentence citing ref.[20] are correcte
Entangling Two Bose-Einstein Condensates by Stimulated Bragg Scattering
We propose an experiment for entangling two spatially separated Bose-Einstein
condensates by Bragg scattering of light. When Bragg scattering in two
condensates is stimulated by a common probe, the resulting quasiparticles in
the two condensates get entangled due to quantum communication between the
condensates via probe beam. The entanglement is shown to be significant and
occurs in both number and quadrature phase variables. We present two methods of
detecting the generated entanglement.Comment: 4 pages, Revte
A 750 mW, continuous-wave, solid-state laser source at 313 nm for cooling and manipulating trapped 9Be+ ions
We present a solid-state laser system that generates 750 mW of
continuous-wave single-frequency output at 313 nm. Sum-frequency generation
with fiber lasers at 1550 nm and 1051 nm produces up to 2 W at 626 nm. This
visible light is then converted to UV by cavity-enhanced second-harmonic
generation. The laser output can be tuned over a 495 GHz range, which includes
the 9Be+ laser cooling and repumping transitions. This is the first report of a
narrow-linewidth laser system with sufficient power to perform fault-tolerant
quantum-gate operations with trapped 9Be+ ions by use of stimulated Raman
transitions.Comment: 9 pages, 4 figure
Quantum polarization spectroscopy of correlations in ultracold bosonic and fermionic
18th International Laser Physics Workshop, Barcelona, Spain, July 13-17, 2009: http://www.lasphys.comN