Research ArticlePHYSICS

Integrated photonic platform for quantum information with continuous variables

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Science Advances  07 Dec 2018:
Vol. 4, no. 12, eaat9331
DOI: 10.1126/sciadv.aat9331

Figures

  • Fig. 1 Configuration of the chip and experimental setup.

    Periodically poled waveguides (1, 2) are the nonclassical light sources. The squeezed vacuum states are manipulated in a reconfigurable directional coupler (DC1) for the generation of two separable squeezed states or a two-mode CV entangled state. DC2 and DC3 are used to separate the pump at ~777 nm from the signal at ~1554 nm. The rest of the network (ϕLO1, ϕLO2, DC4, and DC5) is made of the reconfigurable phase shifters and couplers of the two homodyne detectors.

  • Fig. 2 Generation and homodyne detection of squeezed vacuum states.

    (A) Measured normalized SHG efficiencies Embedded Image for waveguide 1 (blue points) and waveguide 2 (red points) at T = 125°C and relative theoretical fit (solid lines). Pump and second harmonic powers are corrected for Fresnel losses at the output facet and propagation losses (see Materials and Methods). The FWHM of the fit sinc2 are ≃ 0.5 nm, consistent with a ≃ 2-cm interaction length. The waveguides have the same normalized conversion efficiency ≃ 370% W−1 at λ = 1554.45 nm. Measurements are performed in the undepleted pump regime, where the SHG power increases quadratically with pump power. The reported SHG efficiencies have a ±10% relative uncertainty, which is introduced by the error in the power calibration of the used power meters. (B) SR of DC1 (top image) and voltage applied to the LO phase shifters (bottom image) as a function of time. SR measurement is performed by injecting a 1550-nm beam into waveguide 2 and measuring the power at the first output with a photodiode. DC1 electrode is driven with a square wave with 1-kHz frequency and ±16-V amplitude. Distortion of the square signal is due to the limited bandwidth of the voltage amplifier. (C) Noise trace measured from HD1 for a 154-mW pump power. Pump power is measured at the output of the device and corrected for Fresnel losses at the output facet and propagation losses inside the waveguides. Noise variance is calculated on time intervals of 4-μs duration and averaged over 40 sequential traces. Sampling rate is 50 MSPS (mega-sample-per-second). (D) Measured squeezing and antisqueezing levels as a function of pump power for waveguide 1 (blue squares) and waveguide 2 (red circles). Solid lines are the fits made with the function of Eq. 1. Error on the measured noise levels is ±0.04 dB. Pump powers are measured at the output of the device and corrected for Fresnel losses at the output facet and propagation losses inside the waveguides. Pump wavelength is λP = 1554.55/2 nm for waveguide 1 and λP = 1554.35/2 nm for waveguide 2.

  • Fig. 3 Generation and characterization of CV entanglement.

    (A) SR of DC1 (top image) and voltage applied to phase shifters ϕLO1 (green trace, bottom image) and ϕLO2 (red trace, bottom image) as a function of time. SR measurement is performed by injecting a 1550-nm beam into waveguide 2 and measuring the power at the first output with a photodiode. DC1 electrode is driven with a square wave at 1-kHz frequency and ±5.5-V amplitude. Scanning frequency is 1 kHz for ϕLO1 and 10 kHz for ϕLO2. (B) Noise levels measured from HD1 (blue trace) and HD2 (red trace) when the pump beams are in phase. (C) Noise levels measured from HD1 (blue trace) and HD2 (red trace) when the pump beams are out of phase. (D) Noise levels of summed quadratures Embedded Image (green trace) and subtracted quadratures Embedded Image (red trace) when the pump beams are out of phase. Noise variance is calculated on time intervals of 2.5-μs duration and averaged over 10 sequential traces. Sampling time is 20 ns. Measurements are performed with two pump beams with P = 122 mW and λP = 1554.45/2 nm.

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