Time-resolved homodyne characterization of individual quadrature-entangled pulses

We present a full experimental characterization of continuous variable quantum communication channels established by shared entanglement together with local operations and classical communication. The resulting teleportation channel was fully characterized by measuring all elements of the covariance matrix of the shared two-mode squeezed Gaussian state. From the experimental data we determined the lower bound to the quantum channel capacity, the teleportation fidelity of coherent states, and the logarithmic negativity and the purity of the shared state. Additionally, a positive secret key rate was obtained for two of the established channels.

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“…(15). The state condition demonstrates that the reconstructed CM is a bona fide CM i.e., that the CM corresponds to a physical state.…”

Section: Resultsmentioning

confidence: 94%

“…Experimentally, this means that only a few tomographic measurements need to be conducted, significantly reducing the effort to measure these states. To date, several groups have conducted experiments only partially measuring the CM [15,16,17].…”

Section: Introductionmentioning

confidence: 99%

Experimental characterization of Gaussian quantum-communication channels

et al. 2007

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“…However, by correcting for detector losses as done by Wenger et al ͑2005͒, the EPR paradox was indeed achieved since in this case the EPR product is 2 = 0.83, although causal separation was not demonstrated. A degenerate waveguide technique, together with a beam splitter, was recently used to demonstrate pulsed entanglement using a traveling-wave OPA ͑Zhang et al, 2007͒. A distinct difference between the two pulsed EPR experiments, apart from the nonlinearity used, is the method by which the data processing was carried out.…”

Section: B Parametric Amplifier Experimentsmentioning

confidence: 93%

“…The frequency bandwidth of the detection system was too small to resolve successive pulses, which arrived at the detector with a frequency of 163 MHz. In the experiment of Wenger et al ͑2005͒, however, the repetition rate was much lower ͑780 kHz͒, which facilitated the detection stage and consequently allowed for temporally resolved low frequency measurements ͑Smithey et al, 1992, 1993͒.…”

Section: B Parametric Amplifier Experimentsmentioning

confidence: 99%

Colloquium: The Einstein-Podolsky-Rosen paradox: From concepts to applications

et al. 2009

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This Colloquium examines the field of the Einstein, Podolsky, and Rosen ͑EPR͒ gedanken experiment, from the original paper of Einstein, Podolsky, and Rosen, through to modern theoretical proposals of how to realize both the continuous-variable and discrete versions of the EPR paradox. The relationship with entanglement and Bell's theorem are analyzed, and the progress to date towards experimental confirmation of the EPR paradox is summarized, with a detailed treatment of the continuous-variable paradox in laser-based experiments. Practical techniques covered include continuous-wave parametric amplifier and optical fiber quantum soliton experiments. Current proposals for extending EPR experiments to massive-particle systems are discussed, including spin squeezing, atomic position entanglement, and quadrature entanglement in ultracold atoms. Finally, applications of this technology to quantum key distribution, quantum teleportation, and entanglement swapping are examined.

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“…Our OPA, described elsewhere 19 , generates pairs of quadrature-entangled 150 fs pulses with a 780 kHz rate, with a gain g = cosh 2 (r 0 ) = 1.18 corresponding to 3.6 dB of two-mode squeezing. The signal and idler beams are superimposed on PBS1, so that R = 5% of the idler is sent into an APD counter through spatial and spectral filters.…”

mentioning

confidence: 99%

Preparation of non-local superpositions of quasi-classical light states

et al. 2009

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'Schrödinger cat' states of light 1 , defined as quantum superpositions of quasi-classical coherent states, have recently emerged as an alternative to single-photon qubits for quantuminformation processing [2][3][4][5][6] . Their richer structure provides significant advantages for quantum teleportation, universal quantum computation, high-precision measurements and fundamental tests of quantum physics [7][8][9][10][11][12][13] . Local superpositions of free-propagating coherent states have been realized experimentally, but their applications were so far limited by their extreme sensitivity to losses, and by the lack of quantum gates for coherent qubit rotations. Here, we demonstrate a simple approach to generating strongly entangled non-local superpositions of coherent states, using a very lossy quantum channel. Such superpositions should be useful for implementing coherent qubit-rotation gates, and for teleporting these qubits over long distances. The generation scheme may be extended to creating entangled coherent superpositions with arbitrarily large amplitudes.Single-mode cat states can be considered as classical light waves with two opposite phases simultaneously, expressed as C(|α + e iφ | − α ), where |α is a coherent state containing |α| 2 photons on average and C is a normalization factor omitted in the following. The non-classical nature of such states appears most strikingly in the quantum statistics of the electric field: its quasi-probability distribution, called the Wigner function, presents quantum oscillations with negative values between the two classical states. The Wigner function W (x,p), wherexare the quadrature operators of the quantized electric field, can be reconstructed by homodyne tomography 14 from several marginal distributions P θ (x θ = x cosθ +psinθ).Besides their fundamental interest, arbitrary coherent superpositions a|α + b| − α can be used as qubits carrying quantum information, if |α and | − α are sufficiently distinguishable (|α| 2 2). They present many advantages compared with discrete-variable qubits a|0 + b|1 , enabling one to circumvent the fundamental limits of discrete-variable quantum teleportation 7,15 or to carry out loophole-free Bell tests 13 . So far, their applications suffered from two major issues. One was the difficulty to build associated logic gates: arbitrary qubit rotations were believed to require either unrealistically strong nonlinear interactions, or very resource-consuming repeated infinitesimal rotations 8,13 . The other was more fundamental: the complex structure of these states, while offering many benefits, makes them notoriously fragile. For instance, many quantuminformation processing (QIP) tasks require entangled cat states such as |ψ 0 = |α 1 | − α 2 − | − α 1 |α 2 . Theoretically, they can be obtained by splitting a single-mode cat | through lossy channels. The entanglement is created by non-local photon subtraction, by interfering small fractions R of each pulse, phase-shifted by φ, on a 50/50 beamsplitter. Then an APD photon detection in...

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Time-resolved homodyne characterization of individual quadrature-entangled pulses

Cited by 56 publications

References 38 publications

Experimental characterization of Gaussian quantum-communication channels

Experimental characterization of Gaussian quantum-communication channels

Colloquium: The Einstein-Podolsky-Rosen paradox: From concepts to applications

Preparation of non-local superpositions of quasi-classical light states

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