Channel-selective frequency up-conversion for frequency-multiplexed quantum network

TL;DR

The paper addresses the need for flexible, high-fidelity linking of diverse quantum systems in a frequency-multiplexed network by introducing channel-selective quantum frequency conversion (CS-QFC) via cavity-enhanced sum-frequency generation. The authors present the frequency-tweezers concept, enabling selective conversion of a single input frequency bin to a chosen cavity output mode, thereby achieving reconfigurable routing while preserving other channels. They experimentally demonstrate CS-QFC by up-converting light from 1540 nm to 780 nm using a PPLN-WR cavity, show tunable input-bin and output-mode selection through pump detuning, and quantify the bandwidth and efficiency with pump power. A detailed discussion on signal-to-noise performance and use-case scenarios—including channel-selective Bell-state measurements and ROADM-like functionality—highlights CS-QFC as a practical building block for scalable, frequency-multiplexed quantum networks and repeaters.

Abstract

We demonstrate channel-selective frequency up-conversion from telecom wavelengths around 1540 nm for optical fiber communication to visible wavelengths around 780 nm, based on second-order optical nonlinearity in a cavity of the converted modes. In our experiment, we selectively convert a light from any frequency mode within frequency-multiplexed telecom signals to a desired output mode, determined by the cavity resonances. Based on the experimental results of the frequency up-conversion, we derive the signal-to-noise ratio of the process at the single-photon level, and discuss its applicability to channel-selective quantum frequency conversion (CS-QFC) in the context of frequency-multiplexed quantum networks. Finally, we describe specific use cases of the CS-QFC, which show its utility as a reconfigurable switching element in frequency-multiplexed networks, particularly for selectively performing Bell-state measurements between two photons originating from different frequencies.

Figures (10)

• Figure 1: (a) Concept of the QFC-based optical switch. This device extracts only a photon in a specific frequency bin from multiplexed frequency channels transmitted through an optical fiber, while leaving the remaining frequency modes unaffected and passing them on to the subsequent transmission channel. (b) Concept of the channel-selective BSM using the QFC-based optical switch in a frequency-multiplexed quantum network.
• Figure 2: (a) Design concept of CS-QFC. The red rectangular areas each with the width of $\gamma_{\rm bin}$ represent the destinations accessible through the conversion process. Among the input photons distributed over multiple frequency bins (green wave packets), only a photon in a specific frequency bin is converted in a single tweezing process, and the bin can be selectively chosen by tuning the pump frequency. Details are given in the main text. (b-d) Implementation of CS-QFC based on a SFG with a cavity structure around the converted frequencies. These illustrate the tweezing operation of only the photons in a specific tooth of a frequency comb input with spacing $\Delta\omega_{\rm comb}$, by selecting the pump frequency. (b) When the pump frequency $\omega_{\rm p}$ is $\omega_{\mathrm{p},(i,j)}(=\omega_{\mathrm{v},j}-\omega_{\mathrm{t},i})$, only the photon centered at $\omega_{\mathrm{t},i}$ is converted. (c) For $\omega_{\rm p}=\omega_{\mathrm{p},(i,j)} - \Delta\omega_{\mathrm{comb}}$, only the photon at $\omega_{\mathrm{t},i}+\Delta\omega_{\rm comb}$ is converted. (d) For $\omega_{\rm p}=\omega_{\mathrm{p},(i,j)}+\Delta\omega_{\rm FSR}$, the photon at $\omega_{\mathrm{t},i}$ is converted to the neighboring bin centered at $\omega_{\mathrm{v},j}+\Delta\omega_{\rm FSR}$.
• Figure 3: (a) Experimental setup for selective frequency up-conversion and the energy diagram of CS-QFC. EDFA: erbium-doped fiber amplifier, DM: dichroic mirror, SPF: short pass filter, OSA: optical spectral analyzer. (b)Reflectances of both ends of the PPLN-WR, shown in blue and orange.
• Figure 4: (a) The spectrum measured by the OSA2. (b) The Fourier transform of the spectrum in (a). The highest peak frequency is 3.3G.
• Figure 5: The pump power dependencies of (a) the bandwidth of the frequency conversion estimated from converted (red) and signal (blue) light and (b) conversion efficiency ($T$, red) and unconverted efficiency ($R$, blue). The dashed line is calculated by Eq. (\ref{['eq:sfg']}) using $\tilde{\alpha}^{\rm ex} = 7.3e-3\per mW$ and $\tilde{\gamma}_{\rm r}^{\rm ex}=0.17$.