Journal: Light, Science & Applications

Article Title: Hertz-rate metropolitan quantum teleportation

doi: 10.1038/s41377-023-01158-7

Figure Lengend Snippet: Alice’s setup. The 65-ps-long pulses of light are created by modulating 1549.16 nm continuous wave (CW) laser (PPCL300, PURE Photonics) at 500 MHz rate with an intensity modulator (IM). The drive signal is generated by an arbitrary waveform generator (AWG) and amplified by a 25-GHz-bandwidth amplifier (AMP), synchronized with Bob’s clock through a classical channel (CC, red line). A fiber beam splitter (BS) with a ratio of 99:1 and a powermeter (PM) are used to monitor the power of the laser pulses. Subsequently, an unbalanced Mach–Zehnder interferometer (UMZI1, MINT, Kylia) with a path-length difference equivalent to 625 ps is applied to prepare the time-bin qubits to be teleported. Following with a spectrally filtering by a 10-GHz-wide fiber Bragg grating (FBG) combined with an optical circulator (CIR) and a strong attenuation to the single photon level by a variable optical attenuator (VOA), the prepared qubits are sent to Charlie through a 22 km fiber quantum channel (QC), \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Q}{\text{C}}_{\text{A}\to \text{C}}$$\end{document} Q C A → C blue line - featuring 6.8 dB loss. Bob’s setup. Two pump laser pulses separated by 625 ps with the same repetition rate of Alice are generated using a 1540.56 nm CW laser (PPCL300, PURE Photonics) in conjunction with an IM. The pump power is amplified, adjusted, and monitored by an erbium-doped fiber amplifier (EDFA), VOA, and 99:1 BS with a PM, respectively. A polarization controller (PC) and polarization beam splitter (PBS) are used to ensure the polarization alignment for maximizing the efficiency of phase matching in the periodically poled lithium niobate waveguide. The time-bin entangled state of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$|{\varPhi }^{+}{{\rangle }}={2}^{-1/2}({|ee}{{\rangle }}+{|ll}{{\rangle }})$$\end{document} ∣ Φ + ⟩ = 2 − 1 / 2 ( ∣ e e ⟩ + ∣ l l ⟩ ) is generated using cascaded second-order nonlinear processes in the PPLN waveguide module (see Materials and Methods), with mean photon pair number of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mu }_{\text{SPDC}}=0.042$$\end{document} μ SPDC = 0.042 in the experiment. The entangled photon pairs are spectrally filtered into signal (1531.87 nm) and idler (1549.16 nm) ones using dense-wavelength division multiplexers (DWDMs) and FBGs with a full width at half maximum bandwidth of 125 GHz and 10 GHz, respectively. The idler photons are sent to Charlie via another 22 km fiber QC, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Q}{\text{C}}_{\text{B}\to \text{C}}$$\end{document} Q C B → C - featuring 6.4 dB loss and the state of signal photons (stored in a 20 km fiber spool) is analyzed using UMZI2 (625 ps transmission delay, MINT, Kylia), two superconducting nanowire single photon detectors (SNSPDs, P-CS-16, PHOTEC) - cooled to 2.2 K in a cryostat and with 80% detection efficiency, and a time-to-digital converter (TDC, ID900, ID Quantique). Charlie’s setup. The photons from Alice and Bob are projected onto the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$|{\psi }^{-}{{\rangle }}$$\end{document} ∣ ψ − ⟩ Bell state using a 50:50 BS and two SNSPDs with 60% detection efficiency. To ensure the indistinguishability of the two photons distributed through a 22-km-long fiber channel for each, we actively stabilize the arrival times and polarization with an active and automatic feedback system on both \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Q}{\text{C}}_{\text{A}\to \text{C}}$$\end{document} Q C A → C and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Q}{\text{C}}_{\text{B}\to \text{C}}$$\end{document} Q C B → C channels. The timing and polarization feedback signals (Time feedback and Pol. feedback) are generated from field-programmable gate array (FPGA) circuits and digital to analog convertor (DAC) circuits, respectively, and sent to optical variable delay lines (OVDLs, MDL-002, General Photonics) and polarization tracker modules (PTMs, POS-002, General Photonics) to compensate for the time and polarization drifts. Two optical isolators (ISOs) with ~55 dB isolations are used to shied Alice and Bob from attacks. The synchronization (Sync) between the three nodes is performed by classical optical pulses through classical channels (CCs), and assisted with AWGs, distributed feedback (DFB) lasers, photon detectors (PDs) and a tee connector (TC). Both QC and CC are dark fiber cables (FC). The electronic cables (EC) are denoted by green lines (see Materials and Methods for more details about stabilization and synchronization)

Article Snippet: Then the drift signals are fed to two optical variable delay lines (OVDLs, MDL-002, General Photonics) in the two QCs to compensate for the arrival time drifts with a resolution of 1 ps.

Techniques: Generated, Amplification, Transmission Assay