Telecom-compatible cross-band quantum memory via dual photon modes dark-state polaritons

Abstract

Quantum memories are essential components of quantum networks, enabling synchronization, quantum repeaters, and long-distance entanglement distribution. Most ensemble-based realizations rely on dark-state polaritons (DSPs) in $Λ$-type systems that operate at near-infrared wavelengths, such as 795 nm in $^{87}$Rb, far from the telecom band where long fiber transmission is optimal. Here we identify a DSP in $^{87}$Rb that coherently couples two photonic modes at 795 nm and 1324 nm through a shared spin-wave coherence. We derive its field operator and group velocity, extending the Fleischhauer-Lukin model to a dual-wavelength regime, and formulate a memory protocol enabling bidirectional storage and retrieval between the two modes. Numerical simulations of the full six-level dynamics confirm two-way storage and retrieval for both same-mode and cross-mode operation between the two wavelengths. The results demonstrate a dual-wavelength memory that unifies node-band and telecom-band operation within a single ensemble, providing a potential route toward frequency-conversion-free quantum-network interfaces.

Figures (3)

• Figure 1: (a) Atomic level structure supporting a dual-photon-wavelength dark-state polariton. Two $\Lambda$-type subsystems are coherently connected by control fields: $\Omega_{3}$ couples $\ket{e}$ and $\ket{b}$, and $\Omega_{1}$ couples $\ket{f}$ and $\ket{c}$. The lower $\Lambda$ is coupled to a classical control field $\Omega$ and a quantum probe field with coupling constant $g$, while the upper $\Lambda$ is coupled to a control field $\Omega_{2}$ and a quantum field with coupling constant $g'$. (b) Effective level structure of (a). Both quantum fields $g$ and $g'$ are coupled to the dressed state $\ket{+}$ formed from $\ket{e}$, $\ket{b}$ and field $\Omega_3$.
• Figure 2: Numerical simulation of storage and retrieval of a 795 nm probe field in a $^{87}$Rb ensemble of length 1.4 cm. Field amplitudes and selected density-matrix elements at the output end ($z=1.4$ cm) are plotted as a function of the retarded time $\tau=t-z/c$. (a) A Gaussian probe pulse centered at $\tau_{0}=4.3~\mu\mathrm{s}$ enters the ensemble while continuous-wave control fields $\Omega_{3}$ and $\Omega$ follow the dashed temporal profile and are turned off at $\tau_{\mathrm{off}}=5~\mu\mathrm{s}$, then reactivated at $\tau_{\mathrm{on}}=13~\mu\mathrm{s}$. (b) Same as (a), but at $\tau_{\mathrm{on}}$ the control fields $\Omega_{3}$, $\Omega_{1}$, and $\Omega_{2}$ are applied according to the same profile. (c) Same as (a), with $\Omega_{3}$, $\Omega$, $\Omega_{1}$, and $\Omega_{2}$ all turned on during retrieval. Field amplitudes are in arbitrary units; dashed curves indicate the control-field time profiles, whose scales are not to be compared with those of the probe fields. The results illustrate controlled storage and cross-band retrieval of the 795 nm photon through different combinations of control fields.
• Figure 3: Numerical simulation of storage and retrieval of a 1324 nm probe field in a $^{87}$Rb ensemble of length 1.4 cm. Field amplitudes and selected density-matrix elements at the output end ($z=1.4$ cm) are plotted as a function of the retarded time $\tau=t-z/c$. (a) A Gaussian probe pulse centered at $\tau_{0}=4.3~\mu\mathrm{s}$ enters the ensemble while continuous-wave control fields $\Omega_{3}$, $\Omega_1$ and $\Omega_2$ follow the dashed temporal profile and are turned off at $\tau_{\mathrm{off}}=5~\mu\mathrm{s}$, then reactivated at $\tau_{\mathrm{on}}=13~\mu\mathrm{s}$. (b) Same as (a), but at $\tau_{\mathrm{on}}$ the control fields $\Omega_{3}$ and $\Omega$ are applied according to the same profile. (c) Same as (a), with $\Omega_{3}$, $\Omega$, $\Omega_{1}$, and $\Omega_{2}$ all turned on during retrieval. Field amplitudes are in arbitrary units; dashed curves indicate the control-field time profiles, whose scales are not to be compared with those of the probe fields. The results demonstrate reversible storage and cross-band retrieval of the 1324 nm (telecom-band) photon, complementary to the 795 nm case in Fig. \ref{['fig:a_in']}.