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AIP conference proceedings

Pulsed homodyne detection of quadrature entanglement at telecommunication wavelength

Yujiro Eto, Akihiro Nonaka, Yun Zhang, Takuya Hirano, Alexander I. Lvovsky

Published Jan 1, 2009• 0 citations
Publisher

Abstract

We report on the generation of quadrature entangled light pulses at the telecommunication wavelength of 1.535 μm by combining two squeezed pulses. The quadrature phase amplitudes of the entangled light pulses are measured by using two time‐domain pulsed homodyne detectors, which yield one pair of measurement values by single‐shot measurement for each pulse. The entanglement is confirmed with a sufficient criterion 〈Δ[x̂a+x̂b]2〉+〈Δ[p̂a−p̂b]2〉 = 0.64<1.

DOI
10.1063/1.3131302

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We report on the generation of quadrature entangled light pulses at the telecommunication wavelength of 1.535 μm by combining two squeezed pulses. The quadrature phase amplitudes of the entangled light pulses are measured by using two time‐domain pulsed homodyne detectors, which yield one pair of measurement values by single‐shot measurement for each pulse. The entanglement is confirmed with a sufficient criterion 〈Δ[x̂a+x̂b]2〉+〈Δ[p̂a−p̂b]2〉 = 0.64<1.
We propose and demonstrate a scheme to stably generate quadrature-entangled optical pulses using a ring interferometer composed of an optical parametric amplifier and a dispersive media. The entangled light pulses at telecommunication wavelength are generated by combining two squeezed beams. In our scheme, the relative phase between the two beams is kept stable by the ring interferometer and is controllable using dispersive media. The amplitude and phase quadratures of the entangled beams are measured using two time-domain pulsed homodyne detectors. When the relative phase is fixed at $\ensuremath{\pi}/2$, we verify the inseparability of the states by a sufficient criterion $⟨{\ensuremath{\Delta}}^{2}[{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{X}}_{a}({\ensuremath{\phi}}_{0})+{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{X}}_{b}(\ensuremath{\pi}\ensuremath{-}{\ensuremath{\phi}}_{0})]⟩+⟨{\ensuremath{\Delta}}^{2}[{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{X}}_{a}({\ensuremath{\phi}}_{0}^{\ensuremath{'}})\ensuremath{-}{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{X}}_{b}(\ensuremath{-}{\ensuremath{\phi}}_{0}^{\ensuremath{'}})]⟩=0.64<1$ where ${\ensuremath{\phi}}_{0}^{\ensuremath{'}}\ensuremath{-}{\ensuremath{\phi}}_{0}=\ensuremath{\pi}/2$.
We present the generation of pulsed squeezed light at telecommunication wavelength of 1.535 µm via single-pass parametric amplification in a periodically poled MgO-doped lithium niobate waveguide using a novel collinear configuration. The quadrature-amplitude of squeezed light is measured in time domain. The classical parametric deamplification of -3.2 dB and quadrature squeezing of -1.5 dB are observed. The maximum classical parametric amplification of 19.3 dB is obtained at pump average power of 0.47 mW, taking advantage of the tight confinement in a waveguide and high peak power of the pulsed light.
Balanced homodyne detection relies on a beam splitter to superpose the weak signal input and strong local oscillator. However, recent investigation shows that a high gain phase sensitive amplifier (PSA) can be viewed as homodyne detector, in which the strong pump of PSA serves as the local oscillator [1]. Here, we analyze a new method of measuring the continuous variable entanglement by assisting a balanced homodyne detector with the PSA and implement it experimentally. Before measuring quadrature amplitude with the balanced homodyne detectors, two entangled fields generated from a pulse pumped fiber optical parametric amplifier are simultaneously coupled into the PSA. We find that the normalized noise for both the difference and sum of the quadrature amplitudes of the two entangled fields fall below the shot noise limit by about 4.6 dB, which is the record degree of entanglement measured in optical fiber systems. The experimental results illustrate that the advantages of the new measurement method include but not limit to tolerance to detection loss and characterizing entanglement with only one homodyne detector. The influence of mode-mismatching due to multi-mode property of entanglement on the measured noise reduction can also be greatly mitigated, indicating the new method is advantageous over the traditional measurement in multi-mode case.
We report on the generation of broadband pulsed quadrature entanglement by combining two squeezed vacua, which are generated from two degenerate optical parametric amplifiers (OPAs), on a beam splitter. With a single pass through OPA, in which a periodically poled lithium niobate waveguide is used as a nonlinear material, the noise reduction of $3.4\ifmmode\pm\else\textpm\fi{}0.2$ dB below the shot noise limit is observed with a bandwidth of more than 200 MHz. The entanglement correlation or EPR correlation is confirmed with a sufficient criterion $⟨{\ensuremath{\Delta}}^{2}({X}_{a}+{X}_{b})⟩+⟨{\ensuremath{\Delta}}^{2}({Y}_{a}\ensuremath{-}{Y}_{b})⟩=1.28<2$.